Model Engine Maker
Engines => From Plans => Topic started by: petertha on January 19, 2021, 02:21:46 AM
-
I’ve been working on this radial engine on & off for <ahem> more than a few years now. You may have seen some of my prior questions or random posts scattered elsewhere on the forum. Progress has been pretty slow with the usual factors - time constraints, distractions & learn-as-you go snail’s pace. I also had a few unwelcome interruptions with my machines. The drive train on my ’97 Taiwan 14x40 lathe developed problems which took some time to source parts & repair. Then shortly thereafter my same vintage RF-45 mill gearbox decided it wasn’t happy with the world. Ultimately I decided to upgrade the mill but that required some shop shuffling & electrical work.
Anyway, rolling time forward to present day, I might actually be on the home stretch. So I figure it’s a good time to post my prior construction journey and transition into present day work so it will appear as a normal, continuous construction exercise. Actually, looking back at some of my pictures & notes leaves me wondering what I actually did myself, so this documentation exercise will benefit me as well.
I really wanted to build a radial and avoid castings to mess up, so 5 cylinders is kind of the minimum order, at least of the more common radial plans available. The Ohrndorf seemed well designed from my amateur comparisons to other 5-cyl radials. Nothing stood out as radical or unconventional. There is a YouTube video of it running. Hard to tell, but possibly it is an early prototype. I liked the overall proportions & some aesthetic features. Anyways, it ticked most of the boxes for me at the time.
Experience wise, this is my first engine. I’d made a few prior metalworking gadgets, but nothing remotely close to this level. I decided to attempt a single cylinder assembly prototype and if that turned out OK, then I’d carry on with the rest of the engine. The engine has yet to run, so we’ll ultimately see if that path was the right decision. Wish me luck!
-
Design
The engine is designed by Martin Ohrndorf of Modellbau & Technik (Germany). On his web site he offers various other plans if you are so inclined (no personal affiliation). There are also some YouTube videos of his engines running.
https://www.engineman.de/
https://www.engineman.de/produkt/bauplan-5-zylinder-sternmotor/
Engine Specs
Methanol fuel, glow plug ignition
Bore = 24 mm
Stroke = 22 mm
Displacement = 50 cc (10 cc per cylinder)
Weight ~ 1900 g
RPM ~ 950 – 5,500
Outer diameter ~ 225 mm
Length ~ 165 mm
Propeller size 18x14 to 22x12 inch
-
Plans
The 2D hardcopy plans are most certainly derived from a 3D CAD model. They are metric dimensions, corresponding to metric components & tooling. The instructions are in German & quite brief, however I was able to occasionally communicate with Martin by email to answer the odd question.
Once I had the plans, I set about re-drawing parts into my own CAD model. This isn’t a necessity but it certainly helped me on multiple fronts. I was better able to understand the assembly details, make my (imperial dimensioned) shop drawings, design jigs & fixtures etc. Ultimately I made a few changes here & there which I’ll detail, but for the most part stuck to the original design.
I’ll use the abbreviations O5 & O9 for the (Ohrndorf) 5 & 9 cylinder engines respectively. The 05 shares about half its parts with the 09. Unfortunately you need to purchase both O5 & O9 plan sets in order to build the 05. I suspect the O9 came first & the O5 later. The O5 plans have a pseudo assembly sheet that specifies whether to use a stock O9 part, or modify an O9 part, or make a new O5 part. This involves a bit of juggling to keep straight. A single set of O5 plans would certainly have been more convenient, but it is what it is. Who knows, maybe I’ll build the O9 one day.
-
Plans overview & video link
https://www.youtube.com/watch?v=Wod5S4XuKTM
-
Cad pics missing pushrods, carb, inlet/exhaust accessories & some other bits
-
Construction & Design
The engine is bar stock, no castings. Hardening is required on some specific parts. Remaining commercial components include metric fasteners, bearings, spur gears, ring gear, O-rings, circlips & such. I planned on cutting the spur gears for the learning experience, but ended up purchasing them along with the internal (ring) gear because all the gears require modification. Apparently ring gears are a bit involved to (properly) cut teeth profiles in the home shop. I found all the gears readily available at https://www.maedler.de/
RC glow plug ignition was my preference on a first build because it seemed simpler than spark in some respects. I have some RC experience so maybe it was more the devil you know, albeit no prior involvement with multi-cylinder engines or radials. I’ll have to figure out an igniter system when the time comes.
Lubrication is somewhat similar to other glow engines, oil is premixed with the methanol fuel. Specific to the O5, intake charge enters from the rear mounted carb into the crankcase where it mists over the moving master/link rod assembly, then flows backwards out through the induction tubes into the heads. One unique feature of the O5 is that the nose case is compartmentally sealed from the crankcase & partially filled with oil bath for the planetary gear train & cam plates to splash in. I liked this concept because it mitigates an oil pump system. But I’m also wondering what keeps oil from seeping out past the lower, submerged tappets (cam followers). He uses the same bath philosophy on the larger O9, although there seem to be seal differences between engines. Alternately, other glow radials allow the intake mist to continue further forward, flowing into the nose case via openings in the front gear plate. This option is still available to me with some modifications. So I’m still mulling this issue over in terms of how to proceed. I assume the rocker assembly gets lubricated by occasional maintenance oiling & fuel residue working its way between the valve stem & guide. At least that’s how commercial RC 4S engines seem to work.
The pistons have a single compression ring. My plan all along was to use commercial RC rings, specifically from an OS-56-4S engine because the nominal bore dimensions are very close to the O5. I thought this might provide some insurance against making inferior rings & experiencing running problems. I just assumed by matching the O5 bore & piston geometry to the OS-56, I would be good to go. What I didn’t appreciate at the time is that this construction path actually requires more exacting work on multiple fronts, but I’ll save that for later. I still intend to make my own rings because that’s part of model engine building. Whether it’s worth swapping them into this engine to see the difference remains to be determined. Because the liners are also cast iron, I assume they will run in together with the rings, as opposed to commercial RC liners which are typically hard chromed. I’m not sure I will ever fly the engine so I doubt I’ll wear them out between the test stand & trophy shelf.
-
Pics of the prototype. If only I knew what was ahead of me LOL.
-
Peter - this is an interesting project, and one close to me. I am in the process of completing a 3 cyl radial that was part built before the originator died and a friend of his sold it on to me. Mine came with crankcase and end covers, division plate to crankcase, cylinders, heads, crankshaft and conn rods done but no more. And NO plans! So I have had to laboriously measure all the bits I had then design the missing bits to fit into what existed, drawing it all up in CAD, and then go back and modify some of the drawn parts as my thoughts changed.
Interestingly, mine is also designed for glow fuel, as the inlets are plumbed into the crankcase, so I modified the division plate to the gear area to solid with JB Weld so the gearbox/cam area could be lubricated by oil bath. I also arranged the gears and cams very similar to how yours looks, but not nearly so neat!! I have been making progress on this area, having just made the cams, cam support ring and gears including an internals gear and am in the process of fitting it in all together to make sure all fits as it should. Making the gears including the internal gear was all new to me. Made the internal gear using my RF-25 derivative mill as a broach. It all works, sort of, now needs running in.
Will follow your build with considerable and very close interest!!
Chris
PS Can't believe how readily the engine started in the video, it certainly is a runner!
-
Hello Peter,
This is an interesting engine to build. As you said it looks well designed, quite conventional with no obviously 'quirky' bits.
The engine parts you have shown look great. Your write up and presentation are also a credit to you. I will be following your progress as you proceed.
The Ohrndorf O5 and my Seidel ST540 are very similar in both design and size, so we should be able to compare notes.
Mike :atcomputer:
-
I’ve been working on this radial engine on & off for <ahem> more than a few years now.
Too painfully familiar with that phrase. You're intro to this engine build reads very similar to my experience, but I dove into the radial engine world on a 9 cylinder with castings version!
I will be following along closely as well.
Mike
-
Mike.R - Look forward to seeing your build progress. Hopefully my ramblings will inspire you as others have inspired me. Or put another way, provide you specific knowledge of how NOT to do certain things!
Laurentic - Same message. Sounds like a very interesting project. Would love to see some details when you are ready to share.
Vixen - thanks for the interest & nice comments
-
Crankcase 1. The crankcase is made from 2024 aluminum. My notes show that I started the first one in 2017, but there were a few binners along the way.
The turning operations went well, but I ran into issues cutting the cylinder facets. Possibly the setup shifted slightly. But I suspect it was my poor choice gripping the fixture OD with a 3J chuck and/or not properly confirming things where it mattered. Near the end of cutting depth, I noticed the facets were not breaking through quite equally to the internal master rod clearance groove. Not a good sign. Since the internal groove was turned in the same lathe operation as the OD, it could only mean one thing – radial runout. Therefore the facets were not equal distance relative to the CC centerline. Therefore each cylinder assembly would end up slightly up or down & a domino effect of bad things thereafter; piston geometry, compression ratio…. That that would never do. Lesson learned. Aluminum Gods = 1 point, Apprentice = Zero.
The dud part did provide some utility value. I used it to go through the motions of boring & finishing the cylinder skirt holes to tolerance as I was kind on new to boring head operations.
-
Crankcase 2. Turning operations went good. Repetition builds confidence. This time I reverted to an independent 4J chuck for the radial operations to ensure no runout & tight grip. I also made some improvements to the mounting plate. Radial & axial runout was confirmed, this time the facets came out good. The cylinder liner holes were bored. Then while tapping the proverbial last hole (or thereabouts) for the cylinder flanges, I experienced the dreaded broken off tap. ACK!
It was entirely my own fault. The holes were blind end M3 thread. A bit finicky but nothing onerous. After feeling quite confident with my shiny new tapping head, I decided this would be a good application. However, in hindsight, I didn’t properly factor the over-depth allowance as the instructions clearly convey. So with tap firmly stuck in hole, what now. I tried drilling on the end with a carbide, no go. I tried heat. I didn’t have access to EDM or anything like it. After some forum Q&A and very convincing YouTube testimonials, I decided to try the alum solution. It was a disaster. The process slowly turned the part into something that resembled an artifact from the Titanic. The tap was slightly smaller but still there. Rather than take up more space, I’ll just insert a few choice R.I.P. pics if you want to read the original saga on the other forum and we’ll carry on. Aluminum Gods 2 points, Apprentice still zero.
https://www.homemodelenginemachinist.com/threads/broken-tap-in-aluminum-cranckase.26470/
-
Crankcase 3. After 2 warm up exercises, this was the keeper. Well… maybe. Dimensionally everything was good but as I look back on the pics of so-so thready finish, I think my lathe was trying to tell me something even at that point. Forewarning of ominous events around the corner. Anyways, pleasant thoughts for now. This is how it crankcase making SHOULD have gone.
-
Crankcase
-
CC cleaned up a bit, nearing completion
-
Hello Peter,
Top marks for persistence. :ThumbsUp: :ThumbsUp: :ThumbsUp: I suspect I would have given up before the third attempt.
As for Alum to remove broken taps :facepalm: It's usually credited as being the way to go . Now; having tried it several times, without success, I believe it is just an 'old wives tale' which is repeated time and time again by those believers, who have not actually quite got it to work.
Radial engine are a lot of repetitive work. Just stick with it.
Mike :atcomputer:
-
Actually I usex the alum trick when I made my "Mastiff" engine and it worked great. Used a teflon pan, kept the alum mixture saturated and the tap evaporated into bits. No discoloration to the aluminum part.
Ron
-
I stand corrected.
It never worked for me, I only got discoloured aluminium with the broken tap unmarked and intact. Maybe there is more than one substance being sold as 'alum'.
Was it a carbon steel tap or a high speed steel tap?
Mike
-
There are a range of different Alum compounds. Alum alone usually refers to potassium aluminum sulfate KAl(SO4)2·12H2O. I have also used this to sucessfully remove broken HSS taps from brass aluminium parts. It requires time, some heat and some agitation to ensure that there is fresh alum solution in contact with the tap. It has no effect on carbide taps. I don't know if the type of aluminium also has an effect :headscratch:
The picture is what was left of an M2 tap that was broken in a big end cap after alum treatment. It also took the marking blue off the cap.
-
Hello Roger
Where did you source your potassium aluminum sulfate KAl(SO4)2·12H2O? Was it from a chemicals firm?
E-bay may not be the best place to buy it. The product descriptions are not always as reliable as we would like.
Mike
-
Hello Mike,
This came from the lab at work so I am fairly certain that's what I got.
-
Hello Mike,
This came from the lab at work so I am fairly certain that's what I got.
Ha ha, :ThumbsUp: :ThumbsUp: I think I would trust your lab at work any day, compared to the e-bay sellers.
Do they take outside orders????
Mike
-
I stand corrected.
It never worked for me, I only got discoloured aluminium with the broken tap unmarked and intact. Maybe there is more than one substance being sold as 'alum'.
Was it a carbon steel tap or a high speed steel tap
Used grocery store alum.
Mike
HHS tap.
Ron
-
Questionable grocery store alum may have been part of my issue. Another factor may have been this particular tap. It had a coating which may have provided a permeability barrier to inhibit chemical action? The tap is suited for aluminum & cuts like a damn. But all bets off if you drive any kind of tap into the celler. Initially there was an encouraging stream of bubbly-bubbly's coming directly from the tap shrapnel top, possibly acting only on the exposed core metal? I really don't know. I've seen YouTubes where much larger (I suspect conventional bright HSS) taps were fizzed out in no time & native part looked no worse for wear. I treated time lapse YouTube video as one step more believable over well meaning, but likely unproven recipes of Grampa's surefire pickle juice concoctions.
FWIW, after this episode I made a rudimentary coring plug cutter from O1. My edge was just hand ground with a Dremel, but the basic idea was like an annular cutter. Unfortunately without nice sharp sidewall flutes, just reduced diameter for clearance. We're talking only 3mm nominal here. I simulated a broken tap with a pin sticking out of the hole. I peck drilled the material with WD-40. It did make progress, I went in about 0.2" & got bored. I think this might better with proper edge grinding. Maybe even a single edge D-bit principle? The idea is drill out the surrounding area to base of tap & avoid dealing with the tap altogether. Dress the hole, insert tight fitting plug of native material with Loctite or whatever & never tell anyone.
-
Your crankcase looks very nice - shame about the mishap .... :-\
I must admit that I don't see any real reason for not drilling the holes all the way through .... other than the builder knows it's done ....
On a full size it will help preventing it from 'sweating oil' - but I can't see this with this model that has a vacuum in the crankcase.
Another subject - ball bearings works best with an oil mist to lube them ..!!.. no mention of it being mixed with fuel - but the most durable Danish moped from my youth was a single speed SCO where the whole engine and gears are inside the crankcase and lubed from the gasoline / oil mix (5%) and they regularly ran more than 250,000Km. before any rebuild.
So I'm not sure that having a seperate oil section for the cam-box is necessary .... but I will not claim that it's a bad idea either ....
Best wishes
Per
-
Per - there is not just the ball race in the gearbox/cam section there are also the gears and the cams. It was to ensure that these were well lubricated that on my 3 cyl radial I went for a separate section (from the crankcase) with an oil bath, perhaps Peter had the same reasoning I don't know. Different ships different splices as the saying goes, not to say either way is right or wrong, just the way one sees it!
Chris
-
Chris,
My five cylinder 40 cc Seidel ST540 radial engine does not have a separate oil bath for the gears and cam section, it uses the oil mist in the fuel (10%).
My big, 350 cc, Bristol Mercury engines have a wet sump and the oil bath arrangement for the cam and gears.
Seems either arrangement can be made to work.
Mike
-
Mike - exactly!
Like I said, "Different ships different splices as the saying goes, not to say either way is right or wrong, just the way one sees it!"
You pays yer money and yer takes yer choice - as another saying goes!!
Chris
-
:ThumbsUp:
Mike
-
wow tasty project petertha, would follow this one! And love the sound of the engine in the example video.
-
... I don't see any real reason for not drilling the holes all the way through
... ball bearings works best with an oil mist to lube them no mention of it being mixed with fuel
Hi Per.
On my last crankcase I decided to drill/tap the cylinder flange holes right through vs blind. Much easier. I figure the holes will be plugged with threaded bolt or stud, maybe a drop of weak Loctite for good measure & provide some degree of seal. I'm going on the assumption the crankcase can never be under much vacuum or pressure because at any stage its rear end is connected to ambient via the inlet path from carb/manifold. So just trying to make it not be liquid leaky. Every RC engine I've seen has a collective puddle of oil residue in the bottom & suspect this will be no different. In fact I'm contemplating a removable drain plug.
I mentioned in post#5 that oil is premixed with the methanol fuel in typical RC proportions, even though the design calls for nose case with bath oil. I'm just writing up some further elaboration of the lubrication details with pics & example of other radials as it relates to my crankcase assumptions & decisions thus far.
Your comment about bearings is what crossed my mind too. My RC experience has been to remove the bearing shields to allow the oily fuel mist to lubricate the balls & race. No shields on completely internal bearings, leave the outside shield on external facing bearing. So that's another question mark on the stock design. It kind of infers shields are left on for nose case bearings. But if they contain original grease, the oil will act as a solvent over time. If the shields are removed & grease cleaned out like normal exposed bearings, well that's an open door for oil to migrate from nose case to crankcase. But obviously he is running them like that in some manner so I'm perhaps missing something. But for these collective reasons, that's why I'm leaning towards opening up the now solid face plate with aperture's to allow intake mist to extend further into the nose case for lubrication & drop the bath altogether. This will maybe make more sense with my forthcoming pics.
-
Petertha,
Don't have much to add, but this does look like an interesting project. I must say I've always liked radials. I will be following along. I have long considered the big version of the Kinner K5 from SIC. but haven't made any movement on it, To much other stuff going on.
Art
-
OK, you're right - vacuum is technically not correct in this case - more like negative pressure. I guess that it's around 85-95% of the outside pressure ....
-
I have long considered the big version of the Kinner K5 from SIC. but haven't made any movement on it
Art
Hi Art. I know the Kinner you are speaking of. In SIC magazine there was the 1/4-scale gasoline spark version & then I believe a 1/5? scale glow version 'JZ5'?
I actually started drawing those up before going down the O5 path. I preferred the big one but the ignition system scared me off. The smaller one is methanol glow. Kinners are very different animals with the rear bank of gears & individual cam shafts as opposed to single I/E cam plates & planetary reduction gears. Choose your poison. It certainly would make for an interesting project. Its been a while since I dabbled in this but I recall some headscratching on the plans. That may have been the JZ5 though. You have to get all the SIC issues in front of you, there are little nuggets of errata here & there. Kens build if you haven't already seen
http://modelicengine.la.coocan.jp/kinner%20index.htm
I even bought a service manual of the B5 & looked at one at a local museum. Thats what my cad snap shot work in progress is about.
https://en.wikipedia.org/wiki/Kinner_B-5
But speaking only from my own (in)experience level, I thought it would be an even bigger gamble versus embarking on an engine like O5, Jung-5 or Edwards-5. Now having more of an appreciation of work that goes into any engine, I think that was the right choice for me. And I repeat, my O5 hasn't even run! LOL
-
Crankcase Details
The plans call for a tiny 1mm section O-ring groove recess in the front face of crankcase. I think the purpose is to prevent nose case bath oil from exiting along that joint, possibly through some of the faster holes. The gear plate mounts to this face and then the nose section mounts over the plate, both also with O-rings.
As mentioned, I’m still deliberating this nose bath lubrication method & intend to do some simple leak tests with the engine assembled to help me decide. I can still cut this O-ring groove, but I’m dragging my heels a bit. I find them to be a bit fiddly dimensionally so you end up with the fit. If the ring is slightly too proud it will take extra bolt-up pressure to compress enough & still mate the parts. If it ends up too deep in the groove & doesn’t get squeezed enough, then the seal is compromised. Also the groove occurs dangerously close to the facet edges & bolt holes.
So the plan on my radar is to first try making a thin Teflon / PTFE gasket. I found some material samples that vary between only .002-.005” thick. I’m satisfied that I can make pretty clean gaskets just using a scalpel blade along the edge of a simple CAD/plywood cut out template. I may have to make a simple punch for the holes, but surprisingly even drilling the material came out OK as long as there was backing material. A gasket should provide more surface area be re-usable with disassembly.
-
The O5 plans also call for an O-ring groove in the crankcase under each cylinder flange. Curiously the O9 does not have these. It kind of has the appearance of an afterthought. But if it was deemed necessary, than why wasn’t it similarly incorporated into the O9 plans? When I drew up my plans I decided to extend my liners a bit deeper into the crankcase, partially for other reasons. They have a sliding snug fit so hoping this will provide additional sealing area. Also I intend to make similar Teflon sheet gaskets under each cylinder flange.
-
Before leaving the crankcase for now, I wanted to elaborate on the oil bath lubrication details. I mentioned the O5 design calls for the nose housing to be partially filled with oil. The cam plates, planetary gears & bearings spin inside this housing so bath makes great sense from that perspective.
This view shows the approximate oil level based on recommended fill up volume. Notice how the bottom set of tappets (cam followers) would always be submerged in oil. I envision even medium viscosity oil working its way out through the annulus gap between the cylindrical tappet & the bronze bushing ID hole. The tappets are sliding fit & perpetually moving up & down. So possibly even some light pumping action. Maybe any bypass oil volume is minimal & just migrates down the pushrod tube where it ends up in the lower covers. I’m not really sure. Obviously it must work because it’s common to the larger O9
-
Here are some other methanol radial engines for comparison. The common theme seems to be that the gear plate mounted to front side of CC has openings to allow oily fuel it’s to carry forward & lubricate the gears, cams & bearings. There is no compartmental liquid oil bath like the O5 & O9.
OS Sirius
-
Jung 7-cylinder radial (Jung-5 is similar)
-
The Edwards radial has an integrated oil pump actuated off the crankshaft. Oil from external tank is directed to specific areas. It drains by gravity into a lower elevation sump where it is recirculated.
-
Mike (Vixen) has mentioned his Seidel glow radial. I hadn’t come across that engine at the time but maybe for completeness we could have a look at that one too.
I like the Edwards principle. I seem to recall the recommended fuel was straight methanol/nitro and either zero or low percentage (insurance?) oil added because of the pump. I think it’s too late to integrate a similar mechanical pump into the O5, it would require be significant modifications.
I’ve toyed with the idea of external electric oil pump. I suppose it’s maybe kind of a cheat from vintage standpoint, but so are glow plug drivers & other modern necessities. The engine wouldn’t look out of place with external oil feed lines to the nose area. But I know nothing about what kinds of pumps would work so any thoughts welcome.
But if I trust what I think I’m seeing of the mentioned designs which includes established commercial RC engines that probably see much tougher service, then all I would have to do is cut an array of openings into the front gear plate & it might closely resemble that arrangement. Remove the bearing shields as previously mentioned & fingers crossed that rear entering intake mist sufficiently coats the important rotating bits in the nose case.
-
This view shows the approximate oil level based on recommended fill up volume. Notice how the bottom set of tappets (cam followers) would always be submerged in oil. I envision even medium viscosity oil working its way out through the annulus gap between the cylindrical tappet & the bronze bushing ID hole. The tappets are sliding fit & perpetually moving up & down. So possibly even some light pumping action. Maybe any bypass oil volume is minimal & just migrates down the pushrod tube where it ends up in the lower covers. I’m not really sure. Obviously it must work because it’s common to the larger O9
Peter,
It may not do any harm to fit a small baffle plate across the engine more or less level with the oil level shown. It would act as a small oil reservoir. Oil mist would easily find it's way forward, oil droplets could collect in the oil well you have formed, from there it would be distributed all around by the cam gear. True, some oil would migrate down the pushrod tubes but that would be just like every other radial engine, full size or a scale model. It's called authentic.
Just my thoughts
Mike
PS any residual oil left in the crankcase after a run, will drain down into the lower cylinders. past the pistons and into the cylinder heads. There is a danger of a hydraulic lock if too much oil reaches the cylinder heads. It is normal practice to walk the engine through at least 2 complete revolutions (eight blades) to clear the oil before appalling the starter
-
Peter - when I was at sea it was common to use old chart paper (from the bridge!) for making gaskets, or joints as we called them, especially on centrifugal pumps. The joints, smeared in a thin coating of grease which helped when disassembling the parts, worked brilliantly. They are about 0.008" thichness. I guess a decent quality ink jet A4 printer paper 80gms, I say decent quality as some good papers seem slightly thicker and smoother, as opposed to the bog standard cheap crap A4 printer paper one (ie me) usually buys, would work well for you in this instance too and would probably be about 0.005-6" thick max. They work very well, I've not seen them leak, and they are cheap and readily available, and saves having to buy in Teflon or PTFE sheet!
Just a suggestion!
Chris
-
Thanks for the tip. I've heard of gasket solutions like that. Even made from (ideally lowest) currency bills which are tough linen & cotton.
I found this stuff on Amazon, quick shipping &relatively inexpensive. I'm not even sure why its as popular & available as it is. Someone suggested easy release lining for baking sheets or something. None of these parts will see that kind of (oven) temperature. I was hoping it would seal obviously but be somewhat tough & replaceable with disassembly & thin as possible. My only beef with some of the gaskets I've encountered on RC engines is if they stick & hang up anywhere, they are sure to tear. Maybe its the bit of castor oil or long term storage just clamped together but something in the fuel recipe makes an effective adhesive. well, at least my shapes seem easy enough to make by hand & I can avoid a laser or vinyl cutter.
-
PS any residual oil left in the crankcase after a run, will drain down into the lower cylinders. past the pistons and into the cylinder heads. There is a danger of a hydraulic lock if too much oil reaches the cylinder heads. It is normal practice to walk the engine through at least 2 complete revolutions (eight blades) to clear the oil before appalling the starter
Good advice. On my inverted RC engines I disconnect fuel, remove the plug & rotate prop around many times to drain anything that shouldn't be there for that exact reason. Or particularly if it didn't start right away & there was any chance of fuel flooding.
I could probably look it up, but do you happen to know if your Seidel radial has openings to the gears/cams for induction mist lubrication like the other engines I've shown?
-
OS uses a nice circulation system without any pump in their four strokes. It works with the oil that pases the piston ring and ends up in the crankcase. Some of it is hit by the crank and lubes the bottom end and piston pin(s). As it has a positive pressure in the crankcase, the oil is pushed out into the bearings and to the cam gears and shaft. From there it goes up the push rod tubes and lubes the rockers, axle and valves.
And now to the really smart detail - there is a very small diameter short length hole from this cavity to the inlet port, where there is a negative pressure -> the oil is sucket back into the combustion chamber - repeat (as some is burned - you need some in the fuel too).
-
Re the OS 4S, I kind of figured that must be how it works on majority of RC 4S engines because they all have tubes enclosing the push rods & silicone O-ring type seals on both ends of the tubes. When I've dissassebled them the rocker assembly is completely oily looking.The valve cover usually has a gasket, so you know lubrication is working to the extent they don't want it to leak out.
The O5/O9 has pushrod tubes as well but... its another one of those things I'm scratching my head a bit now that I'm getting into it. The tappet bushing is kind of a conical external shape, presumably so the tube can rest on it at a 3D angle (maybe with a bit of mitering). Where it gets interesting is the rocker perch end. Now the receiving tube hole has to be at a funky 3D angle because the inlet & exhaust pushrods are at different angles based on the forward/aft positions of cam plates. Then he has a lateral set screw through the perch base that indexes into the tube. I'm no expert but it looks fiddly to me.
Then when I look at the the shop made radials like Edwards & Jung, they all have exposed pushrods, no tubes at all. So are the rockers getting sufficient lubrication from valve/cage blow by or is an occasional manual drip before running all thats required? I'd like cover tubes & I've spent some time looking at the motion geometry. Its yet another kick-the-can-down-the-road theme, but my plan is to drill oversize holes in the rocker perch & then figure out some kind of rubbery fitting that will both capture the tube & seal it a bit. I've had a little bit of experience making rubbery-like urethane or silicone parts from aluminum molds. These are pretty teeny. But I'm getting ahead of myself.
-
OS uses a nice circulation system without any pump in their four strokes.
Some OS engines used one form or another for a very long time. FS-120 Surpass since the 80's. SurpassII versions of FS70 and 91 also used it (case vented to intake manifold). The most recent iteration you describe above was used in the first Alpha series (https://www.os-engines.co.jp/english/line_up/fsalpha56/index.htm) which added passages by the cam followers (only low volume car versions of FS-26S-C and 40 had this prior) and the hole to the intake in the head. They have reverted to a normal case vent in the II versions of FSa-56 and 72. In the real world, with overly rich needle setting, excessive oil in the fuel, inverted installations, that system caused inconsistent running in the smaller engines due to randomly pulling rather large volumes of oil when orientation promoted it. I have added this system to several engines and never noticed unusual behavior, but I don't run typical fuels or oil ratios. OS rarely used gaskets.
Some complained about rusty bearings due to the closed case. I ran mine up, got them hot and let it idle for a while prior to shutdown. Some people like to push after run oil into the breather vent, and this wasn't possible with the closed system. There was one I left on the test bench for a week and ended up with bad bearings.
Exposed rockers need regular oiling, just like full scale. Even enclosed valve train can end up quite dry in RC four strokes. Varies with type of oil, how hot it runs, fits of parts, though most seem get oil. Valvetrain doesn't need much being properly hardened. Until recently as mentioned above, rockers were lubed by want managed to squeeze by the followers and valve stems.
-
Interesting, dieselpilot. I'm probably mistaken then about valve cover gasket being present. I cannot honestly recall which of my dads 'castor-bunged' engines I disassembled (there were so many haha). Thought it was an OS but like you say they have spanned many years. Looks like the newer OS 4S are no gasket. I might be confused with YS which was more familiar to me, but maybe that was related to the air box boost? Interesting the Saito gasoline (with premix oil) has gasket.
Maybe the silicone fittings at the ends of the pushrod tubes are more about fitting up the 3D angle geometry & withstanding vibration etc as opposed to sealing oil residue.
Also attached OS methanol snip regarding crankcase drain.
-
You got a bit ahead of me, had a busy evening yesterday. The small Kinner was a 1/6 scale. I did Talk to someone at the NAMES show in Detroit who built Jemma and said there were discrepancies and get in touch with him if I built that. Didn't get anywhere with that one either.
Art
-
Ya. This is just my own beginner opinion, but design discrepancies scare me. Especially if discovered late in the game. I'm sure all plans have the potential for boo-boos, its just to what degree. I get it, these creations originate from human minds. And many designs created in the absence of modern software to validate things. And we have to pick a project we enjoy & stay motivated through tough times. That's kind of how I landed on this engine for better or worse. I figure if I can build it & get running, I'll be in a better position on future projects. Happy to pay my dues following others with much more experience than me.
Just as an aside, I mentioned the Edwards (free plans) & Jung designs (purchase plans) were next in line on my list
https://www.cad-modelltechnik-jung.de/construction-plans-model-engines.html
Jung recently revamped his website & lots of links of running engines, which for me is a confidence builder
I like this link. Lots of construction pics & he had the kahunas to strap it in a model. Its not an gasoline/ignition like Jemma but 7 cylinders.
http://philsradial.blogspot.com/
-
OS machining has been very nice for a very long time, so they don't use gaskets in the four strokes for the most part. YS on the other hand, operation depends on proper sealing. Another intersting note is that virtually all steel components of the better glow engines have been coated for rust for over a decade now.
Saito have a similar design with the pushrod covers. They use fairly thick gaskets at the perch to seal and a sleeve at the follower guide. https://www.horizonhobby.com/product/pushrod-cover-and-rubber-seal-2-ca/SAIG60R340.html
-
Crankshaft Intro
The O5 crankshaft was turned from a bar of 1144 SP (stress proof) steel. This was the first time I've machined this material & I don’t have much comparative experience to similar tougher alloys like 4xxx series, but I was pleased with the results. The material specs are: 83% machinability (1212 reference = 100%), 132 ksi tensile, 100 ksi yield, 27 RC hardness. It turns & finishes well with my offshore carbide inserts. But the important claim to fame by other engine modelers is that it’s less prone post machining stress relief distortion on parts like crankshafts with irregular geometry.
The crankshaft is solid, by that I mean the counterweight profile and crankpin are cut from the same stock (as opposed to a built-up crankshaft with separate components). While probably stronger, a one piece also means quite a lot of waste material removal to get down to the much smaller shaft OD area.
-
Rough turning was relatively straightforward, I just took it easy for the most part. It was around this time that my complaining lathe threw in the towel, even with moderate DOC. The clutch started rattling (disengaging), the finish was progressively crappier & I could feel this was more serious. So, reluctantly I had no other option but to remove the stock before the critical finishing stage & deal with the lathe.
The repair was a long, drawn out process. I won’t go into details but some of the story is documented here. https://www.homemodelenginemachinist.com/threads/14x40-lathe-power-feed-improvement.27629/#post-318716
The problem likely originated on the factory floor – somewhat flaky design, skewed power feed rod & misaligned related driveline components. I hope I don’t have to repeat this anytime soon, but the upside is that it’s never run better & I have a deeper understanding of my machine.
The rear end stock was held in 3-jaw and front end in live center. With the rough turning complete, it was critical dimensions time. There are 4 bearing races and a spur gear which are slip fit on various OD sections. In retrospect this was my first real go at having to produce OD’s within a couple tenths and simultaneously with good finish. My lapping methodology was kind of crude, & learn as you go, but eventually the job got done. It is important to let the part heat stabilize to room temp after turning because that can easily trick the OD measurement. Something I would now do when it comes to bearing fits on a CS or part with a lot of time invested is turn or utilize a dummy gage pin to establish the bearing fit beforehand, then use the same (quality) micrometer to translate that dimension to your part as you transition from turning to finishing or lapping. The last of the turning related operations were completed – groove for retaining ring and (hand) threading for the spinner nut. The part was removed from the lathe & band sawed to rough length.
-
Crankpin Roughing
I decided to rough most of the excess material in the mill leaving a remaining square of crank pin material for finish turning in the lathe. This setup also allowed me to make a center drill mark to the exact crankpin throw radius and also drill/tap the 2 holes for the added counterweight slug fasteners.
-
Crankpin Turning
Next I made an aluminum holding fixture that was a close sliding fit over the finished shaft OD. It has 2 through holes to match the counterweight tapped holes. It also has a milled flat on one side parallel to the bolt hole line, a reference surface for later. This fixture provided something for the chuck to grip & the bolts acted as kind of dog to transfer rotation. The crankpin center was dialed in with a DTI against a pointer rod extending from the tailstock. With setup established, the crankpin was turned down to diameter as well as the rear face of the counterweight profile and a thin boss profile for the master rod bushing. I tried a different style of lapping tool which was kind of a squeeze clamp affair.
-
Counterweight Profiling
Back to the mill. With the holding fixture still on & reference surface presented to the vise, the counterweight profile was cut out. Then the roundover profile was milled & hand filed away using a slip on guide bushing.
-
Crankshaft Counterweight
The design calls for an additional counterweight mass which is bolted to the matching crankshaft profile. One of those 5 minute jobs that took 3 hours. It has a relief arc cut to accommodate the master rod, but its center occurs at a different center than the OD, so required 2nd setup in the 4 jaw. I integrated that registration point in the same fixture used to hold the crankshaft for crank pin turning. Brass face mills really nice with the sharp uncoated inserts used on aluminum.
-
Some partial assembly at this point
-
Congratulations on a very important part made, to a high degree of accuracy :ThumbsUp:
I do not see what holds the gear for the camshaft i place - key or ?
Best wishes
Per
-
Hi Per. The designer recommends high strength retaining fluid (Loctite) for the gears. So the spur gear ID on the crankshaft OD (where there is very little hub meat left for a key anyways). The ring gear OD on the cam plate part. And the face to face mate surface between the 2 idler gears. I'm a little concerned by the last one. I may silver solder those. But holding off until it comes to clocking the timing. I'll determine which are the better gears to lock & which can be allowed to move into position.
I was a bit apprehensive about 'glue' but I've also seen many example where cam lobes & such were attached this way. I actually don't know what kind of forces are involved on the planetary gears, their sole purpose is to lift the valve rockers against spring pressure.
-
Sorry for the long lapse again. I will now continue on with the cam drive assembly. The O5 is similar to other radial engine layouts where the crankshaft drives a planetary gear reduction assembly, the output of which is connected to two separate cam plates. One plate is dedicated to intake, the other to exhaust where cylindrical cam lifters ride along the cam profile. As the cam lobe raises the lifter, the connected pushrod act on the rocker arms to open the valves.
The O5 planetary gear is a 4:1 reduction ratio. A 15-tooth module-1 crankshaft gear drives a 15-tooth intermediary gear which is sandwiched against a 10-tooth gear, which drives a 40-tooth internal (ring) gear. The intermediary 15/10 tooth gear cluster rotate together on an idler shaft. Because of 4:1 ratio, each cam plate has 2 identical lobes 180-deg apart for 2 corresponding events per single cam revolution. The intake & exhaust cam plates are phased angularly to each to achieve timing relative to TDC. Both plates are attached to a cup which contains the ring gear. Here are some overview sketches. Hopefully this will make more sense as the parts & assembly are shown in real life.
-
The gear plate is made from 2024 aluminum. It houses one of the 4 crankshaft bearings on the rear side & also holds the idler gear shaft on the front, nose case side. The plate attaches flush to the crankcase front face retained with M3 screws & also snugly fits the crankcase ID with a matching boss. The plans called for 1.5mm OD O-ring seal on the internal boss & another on the lip OD to seal the nose case.
I mentioned earlier that the original O5 design called for the nose case chamber to be partially filled with oil to splash lubricate the gear & cam assembly. The O-rings are to seal this bath oil from the crankcase & the outside world. But I was becoming less comfortable with potential oil migration issues & dragged my feet on this matter for as long as possible. For example, even though the rear bearing was presumably left shielded I thought oil would eventually get in behind the shield, dilute the grease & ultimately leak into the crankcase. Then the risk becomes hydraulic lock on lower cylinders. Also, because the lower cam lifter bushings would always be submerged in oil, it seemed like another potential migration path out.
So, after a lot of deliberation, I finally decided to abandon the oil bath mode. Rather, I made a series of modifications to my existing parts & this gear plate was one of them. Therefore, you will see a mashup of old & new pictures, hopefully it’s not too confusing. I decided to subsequently drill an array of passage holes in the front plate to allow intake mist charge originating from the rear via the carb & crankcase, into the nose case & lubricate the gears & cams that way. This is actually the established lubrication method of other commercial & shop made radial methanol glow engines, so hopefully will prove to be the right decision. For added insurance I will make a threaded/capped port hole on the nose case to squirt lubrication oil in prior to running. I'll be careful during break-in runs to see how wet things are. The O-rings are already done & will still serve their intended purpose.
-
The basic gear plate profile was turned from solid bar. The main diameters & bearing counterbore were done in one setting. The O-ring groove dimensions also need to be done at this point before removing the part. The grooves were a bit fiddly to obtain the right fit to the matching components. I’ve seen some O-ring groove formulas that get you pretty close, but in the end, it was a progressive trial & error thing. I used 70 durometer Viton O-ring cord & spliced a custom ring using CA glue. That part went amazingly well. If you ever need oddball O-ring diameters to make, I can recommend this as a cost-effective alternative.
-
Pictures showing the stock gear plate design confirming fit to crankcase.
-
Once the plate was machined, it was set up in rotary table for hole drilling. I trusted the CAD pitch circle calculation to drill & ream the idler shaft hole using mill DRO.
-
Then I made an MDF fixture to hold the plate, return to lathe & counterbore the relief for idler bearing spur gear.
-
Here are some pictures of the subsequent plate modifications to drill the array of oil mist holes. Of course, that required a new fixture to reestablish the geometry which would have been SO much easier the first go-round. I managed to get the 2 lower apertures slightly intersecting the gear cluster so hoping it will get directly misted.
-
I think that there is a very good chance that you will be very happy with you desicion to use mist lubrication :cheers:
-
I purchased the steel module-1 spur gears from Maedler, the same company I got the internal gear from https://www.maedler.de/
Originally, I contemplated making the spur gears myself. But these were reasonably priced, high quality & each gear requires quite a bit of modification. At my snail’s pace construction, this was probably a good decision in hindsight.
For the crankshaft gear, I first machined a closefitting aluminum pot chuck in the lathe. Then swabbed the ID surface with acetone. Then without disturbing this setting, inserted the gear blank which was as a tight push fit on the teeth & back face. Checked the bore with a DTI, all good. Then I spotted some CA in glue among the teeth to prevent it rotating loose & a spritz of kicker. Then bored out the ID to fit the crankshaft diameter & faced/profiled to length. The steel was reasonably hard but machined well. The glue held things firm, even during interrupted tooth cuts.
Once the assembly was removed, my plan was to heat the assembly with light torch heat, expand the aluminum more, break down the glue & gear would drop out. It put up a bit more resistance than I expected but eventually parted ways with slight persuasion from a rod. The crankshaft OD was just a hair over diameter near the rear stop so a bit of lapping compound got the two-parts fitting snug. The gear will be permanently bonded with Loctite retainer.
-
The 15T idler gear blank was held in a 5C collet for opening up the bore & machining to length. The 10T gear was positioned on an axle fixture to turn down a portion of the gear which then fits inside the 15T bore. The inner 10T gear bore rides on an idler shaft. The gear cluster will be bonded together with Loctite retainer.
-
The gear idler shaft is made from 5mm O1 tool steel. The end has a M2.5 threaded hole for flathead screw that retains a brass end washer in position. Including some pictures of one of my (many) lapping trials. My experience with drill rod is that is always within the stated tolerance, but is often eccentric in cross section. So, the purpose of lapping here is to bring it to size with appropriate finish, but also make it circular section. Here I have a steel clamp with a thumb screw tightening nut. It holds a sacrificial aluminum lap, slit through & also some internal relief slots made with a jeweler blade in scroll saw. I have a selection of inexpensive (AliExpress/Ebay) diamond lapping compound of graduated grits. The method worked reasonably well. But I have subsequently come up with an easier, less messy tool which is now my go-to method. I’ll show that tool a bit later.
After lapping & parting off, I torch heated & oil quenched. Then into the toaster oven to tan brown. I discovered it is sufficiently hard because I discovered the countersink was a teeny bit shallow & had to grind it bit to deepen, because my HSS tool just rubbed it. All good, everything seems to run smooth.
-
Cam Plates. I only have limited hardening experience with O1 tool steel & that was confined to relatively simple parts using a torch. I don’t have heat treating equipment, but I discovered a local fellow who does heat treating for knifemaker community. He has all the appropriate equipment & experience with the many flavors of air quench blade steels. Considering the work that would go into producing the cams & the form factor, I had visions of it distorting into a Pringle chip, or cracking across the internal holes. I figured successfully heat-treating knife blades would present a tougher challenge than my cam plates. So, I sourced the (Starrett brand) A2 from my local KBC dealer, choosing a bit thicker Imperial stock which had to be thinned to prescribed metric dimensions.
I made a simple aluminum fixture puck for the lathe with 2 threaded holes. After a facing the puck face true, the A2 stock was mounted with matching screw holes & brought to thickness. The ID was rough bored with annular cutter then finished with boring bar.
-
The cam outline was band sawed roughly to outline but leaving 2 sacrificial ears with the original screw holes, which now served second duty to secure the part to the mill fixture. The ears correspond to where the cam lobes will occur. The lobe profiles are identical shape between intake & exhaust cams, but the four M3 mounting holes are angularly phased different to each other to achieve proper timing. One plate has M3 clearance holes, the other plate holes are threaded. Therefore, the cams don’t lend themselves to be stacked together to make both intake/exhaust plates simultaneously.
The rotary table was first zeroed to the quill center. Then the fixture assembly was positioned concentrically on the ID hole with DTI & also along an edge of rectangular jig plate. Now the M3 holes could be drilled as well as the array of larger holes. These holes were a bit of foresight on my part relating to the same possibility that mist lubrication might be in my future, because drilling these holes after the cams were hardened would be very difficult. So, I came up with a CAD pattern which I could also replicate on the ring gear cup which the plates mount to & this would allow mist lubrication to flow through from rear to front. I was a bit concerned these holes would be great places for the cam to crack during heat treating but it turned out OK. Actually, the plans called for larger holes & non-symmetric spacing so it was a bit of faith.
I used an endmill & rotary table to cut the main profile, which is the valve closed, non-action surface. Overall, it went according to plan. Just have to be careful about entering & exiting the cut accounting for RT direction & backlash. The lobe ramp profile shape was created by the radius defined by the EM diameter as per the plans. You can see I have a small Sherline 4” RT clamped in my mill vise bolted to an intermediary plate held in my main 6” vise. I feel the RT was accurate enough but found myself doing light cuts because I could feel the cutting action on the handwheel. Next time I would use my larger RT which is a bit more solid.
-
The cam part was released from the mill fixture & ears band sawed off. Now I could transfer to another lathe fixture, this time with a boss which fit the cam hole ID & retained with screws through the holes. Now I could turn the cam lobe OD which is the valve open segment. That just left a small radius to blend the ramp segment to the open segment which was done by hand. I didn’t take a picture but basically, I blued the part, scribed a line using a radius gage tangent to both surfaces & filed it to shape. That left finishing the outer profile with rubber abrasive in a Dremel.
-
Once the cams were finished, I shipped them to the heat treat person along with some sacrificial coupons. A few weeks later they arrived back by mail. He verified the hardness & came as you see here. There was negligible distortion. They fit the ring cup the same way. The bolt threads engaged nicely so I was happy.
-
Some partial assembly pics
-
Wow! Very nice work Pertha! The cams look beautiful! Did they just come back the nice black color? Or is that the color of hardened A1? Regardless,it looks great.
Kim
-
Thanks Kim, yes that's the way they came. I'm not quite sure how far the black actually penetrates. It doesn't scratch or buff off easily. I guess we'll see after running. I know he quenches A-steel blades between slabs of ground aluminum to quench & also help prevent distortion. My memory is foggy now but he also mentioned salt bath. Would that be for the secondary tempering stage? I've been meaning to call him back because I will have some more parts to do. Unfortunately timing didn't work out for a shop tour, I would have liked to see it.
-
The 40-tooth module-1 steel ring gear blank I purchased needed to be reduced in diameter & also in thickness. I purchased 2 gears just in case, but managed to get it completed on the first try. I first made a lathe fixture with a shoulder boss sized to tightly fit the tooth crowns. With this boss feature turned, the gear was positioned to preserve concentricity. It was held with a CA glue on the fixture back face & a clamp plate sandwiching the gear to the fixture with a cap screw. It held sufficiently tight & the material machined quite nicely. I was able to turn the OD to size by eventually cutting both the gear & fixture cap until there was some remnant gears to trim off. Maybe there was a better machining sequence to accomplish this, but the end result doesn’t leave much of a gear one way or another. It worked out in the end
-
The ring gear cup is made from 2024 aluminum. It is supported on the crankshaft with the 2 smaller intermediary bearings. Once the timing is set, the ring gear is permanently bonded to the inside cup lip with Loctite. The cup has 4 countersunk holes for the M3 flathead screws to secure the cam plates. The cup was subsequently drilled with lubrication mist passage holes that match the holes in the cam plates so that lubrication mist can frow from crankcase into nose case & hopefully wetting everything in it’s path with oil film. Aside from careful turning to match all the fit tolerances, it was pretty straightforward machining.
-
Ring gear cup machining.
-
Subsequent modifications to add mist passage holes.
-
More beuatiful parts and nice description of the proces of making them :ThumbsUp:
I got one question though - as you can't move the cams nor the rest of the gears - did you use a slow setting Loctite, so you can keep on 'turning the assembly until you are happy with the timing ?
-
Excellent work.
-Bob
-
Nice work, I always follow along on radial builds!
-
I got one question though - as you can't move the cams nor the rest of the gears - did you use a slow setting Loctite, so you can keep on 'turning the assembly until you are happy with the timing ?
Thanks for the compliment. I haven't timed the engine yet, that part is coming, hopefully before hell freezes over LoL. The plan is to fix the crankshaft gear and also fix the idler gear cluster together face to face. That secures that relationship & leaves the remaining ring gear OD temporarily able to slide within the ring cup ID, thus cam plate pair can rotate independent of the crankshaft in this setup mode. But since the cams are bolted together through the cup, they cant vary between each other. I will make an arbitrary witness line across both ring gear & cup edge. The business end of the engine and one cylinder stack are temporarily assembled. Then an indicator probe in the glow plug hole to identify TDC. The target cam position occurs when intake & exhaust are mid way of their 20-deg overlap relative to TDC. So comparing this actual event point (indicated by valve lift) will reveal how far out it is in CS degrees. Divide by 4 equals how much to rotationally adjust the ring gear relative to cup using the witness line as reference guide. Hopefully converge after a few iterations. Once convinced, make a suitable sacrifice to the engine Gods & glue the ring gear in this position & mark the intersecting teeth. At least this is my plan, reality may have something different to say.
I'll have more to say about timing in a few posts. I was curious to figure out what the exact resultant engine time actually was & how that compared to other engines. The plans didn't specify this. I mean intake/exhaust open/close relative to TDC, BDC etc.
-
Looking good :praise2: :praise2: :wine1:
I have a similar set of Chinese diamond lapping pastes :)
-
Before leaving the construction aspect of gears & cams for now, this might be a good opportunity to discuss the engine timing. The O5 plans provide all the necessary dimensional information to construct the cam drive train, but the specification sheet did not express inlet/exhaust timing in terms relative to piston TDC/BDC. I’m not sure why some engine designers omit this information, but it is what it is. The instructions are also somewhat ‘abbreviated’ in terms of how to set the timing. Translation from another language probably doesn’t help matters. So, I wanted a firmer grasp of this stuff & also understand how the O5 timing compares to other 4-stroke (methanol/glow) model engines. Not that I felt qualified to modify it, but more for the sake of interest & future projects as well.
What follows is not intended as a detailed How-To. More of an overview of how I stumbled my way through this timing aspect, which is kind of a reverse engineering process starting with the parts drawings & references. Hopefully this will be of value to others.
First, one needs to know the gear ratio between the crankshaft (CS) & cam plate. As mentioned, the O5 planetary gear ratio is 4:1 which comes as a result of each gear-to-gear tooth count in the train from CS to idler cluster to ring gear. The rotational direction is also important. The O5 cams rotate in the opposite direction of the CS as shown by the sketch looking at the engine from the front.
-
One needs to understand the intake & exhaust cams relative to each like a sub-assembly. The exhaust cam is to the front, intake to the rear, specifically orientated to one another with index bolt holes. Each cam pushes on its own dedicated lifter & respective pushrod / valve rocker. It is also important to be aware of the lifter geometry relative to the overall assembly. The sketch shows the O5 lifter action (red lines) extending radially from the CS center. Therefore, the cam contacts are occurring at different clock positions relative to the cylinder engine datum. This is important because other radials may orient their lifters differently. For example, if the lifter axis were coincident to the cylinder center (purple line) then the inlet/exhaust timing relative to TDC/BDC would be different on the exact same cam plate, all other things equal.
-
This sketch is a bit busy, but shows how I then superimposed the lifter reference lines on the cam assembly. Then I determined the corresponding rotation angles marking the beginning & end of each lobe event which correspond to intake open, intake close, exhaust open, exhaust close.
-
These numerical values were input into a homebrew spreadsheet from which I could calculate timing metrics in more familiar terms relative to TDC & BDC. I also determined valve overlap, lobe separation angle & made a plot to better visualize things.
-
(Note, I posted a variation of this information elsewhere on the forum, so if it looks familiar, that's why)
I recently found this website which is an excellent resource for model engines http://sceptreflight.com/
What is particularly useful is the library of past engine review articles from magazines & other sources back in the day. Some reviews were very detailed. They disassembled, measured & photographed parts & assemblies & bench tested engines to provide useful power & rpm information. So just for the sake of a gut check comparison to my radial, I limited the data extraction to O.S. 4-stroke engines, although other brands are also represented. O.S. are generally considered to be reliable, powerful sport engines & encompass a wide range of displacements & layout’s including multi-cylinders. Of course, many design factors influence resultant engine timing which is outside the scope of this post. I have also been adding a few engines of interest here & there so don’t read too much into the individual data points. It’s kind of a work in progress. You can see the O5 timing as it relates to other engines. The overlap is relatively narrow & (I think) the values suggest conservative timing, but I’ll leave that for you to decide.
-
Also, because there have been a few builds of the Edwards 5-cylinder engine posted on the forum & the two engines are similar in many respects, I did a timing plot overlay for comparison. If anyone spots any errors along the way, please let me know.
-
The nose case was machined from a round of 6061-T6 aluminum. I can’t recall if I chose incorrectly from my intention to use 2024 or it was my subconscious saying ‘odds favor a mess up somewhere along the way’. I decided to machine the outside profile first, then flip the part around to do the inside surfaces. This seemed like a better way to grip the part for ID hogging & hopefully concentricity on internal features.
The front was first drilled for the crankshaft clearance. Then a recess feature counterbored for the front bearing, which is a light press fit. The section profile contour was defined in the plans by various blended radii. I generated a series of corresponding X,Y intercept dimensions in a shop drawing. I cut these stepover terraces with a parting tool & blued the surface. Then finished the surface with file & sandpaper until the blue was gone & finished off with a 3M pad. I left the part this way in the chuck & transferred to bandsaw vise where it was lopped off.
-
The plans had some internal pocket relief (milling) features & contouring around the lifter area which I stared at for a long time. It looked very nice & it yielded a slightly thinner case section in certain areas. But to my eye actually seemed a bit thin around the front mounting bolt head recesses. So, I opted to modify the section profile a bit so that all the internal surfaces could be done in the lathe in one setting as a series of steps. This provided a bit more meat around the bolt heads, but same annular thickness around the bushing radial holes. It cost some grams of aluminum which I didn’t really care about anyways but erred on the side of bit more strength since it was 6061 & not 2024. I also wasn’t entirely clear about how the pushrod tubes were being retained on the conical lifter bushings, but trusted the plans for now.
-
Next step was to chuck the part for the rear side internal cavity work. A spacer was positioned between the chuck face & nose as a mechanical stop. I wrapped some tape on the OD surface to protect it from jaw bite. The DTI said my 3-jaw was accurate, but in instances where required, an extra layer of tape under a jaw allows you to micro-shim. In hindsight the 4-jaw chuck would have been a better choice on 2 counts. You can dial it in exactly & also it provides one more gripping surface. This can be an issue on thin-walled parts where high initial gronk when the part is solid can result in slight deviations when the internal surface is machined out. Another thing I have subsequently learned is that not all tape adhesives play well with cutting fluids. They can dissolve, become unglued & I suppose risk the jaw grip.
I now favor an aluminum tape for protection applications like this. It also works well in shimming applications where its preferrable to pre-attach the material. I think this tape is used for furnace duct work.
So, after some material hogging, I just had to be careful as I approached the ID lip surface which becomes quite thin & must fit the gear plate OD properly c/w with its O-ring in place. It’s important to let the part cool to room temperature & take spring passes at different feed settings.
-
Some interim assembly testing pictures
-
Next step was to make a fixture to hold the nose case by the ID lip so that the part could be gripped in a rotary table. It has a threaded hole for a retention stud. After some trial fit-ups that were a bit too tight & concerning moments where the parts were firmly stuck, I put a smear of anti-seize on the surface.
The fixture/part assembly was gripped in a RT & 4-jaw chuck & 5 bolt holes drilled & counterbored. Now the RT was flipped upright. I used a parallel & DTI to register what is equivalent to horizontal reference off 2 bolt holes & then proceeded to drill & recess the holes for the lifter bushings. These are offset on either side of center nose case center & also offset fore & aft corresponding to the respective cam plates positions.
-
Nice work Peter! :popcorn:
-
Hi Peter
I’ve been following along; your radial and my rotary share many similarities. I especially enjoyed your discussion regarding the cam disks.
Your work is superb.
-
Thanks for the kind words.
The lifters (or maybe they are called tappets, I’m never sure) are made from nominal 3mm O1 tool steel. The internal end is a dome shape which runs along the cam plate profile. The external end has a partial depth 2mm OD spherical socket seat which mates the ball ended pushrods. The lifters slide up & down within bronze valve guides. So, I made some test guides first so that the drilled & reamed bores could be used as guides for lapping the lifter stock OD.
The male dome profile was formed by a ball turner accessory. Then the part was flipped in the collet, trimmed to length & the female radius profile made with a ball end mill. These lifters were sent at the same time to the same heat treat guy who did the cams so I wanted to get the finish as good as possible now. The lifters would have been easy enough to heat treat with a torch to ‘some’ level of hardness but I wanted them to be a few points softer than the resultant cam plate hardness so as to preferentially wear the (easier to replicate) lifters. I didn’t trust my repurposed toaster oven to deliver accurate temperature for tempering. The male end was polished by gripping in my Dremel chuck & lightly running in a shallow well drilled in MDF wood with a smear of compound.
-
The lifter guides are made from bronze as per plans. The turning profile is pretty straightforward. I used my 5C collet chuck & sharp, uncoated insert like I use on aluminum. The holes were drilled & reamed. Its interesting when you make a bunch of the same parts, you gain an appreciation for variation. Some lifters slid nicely in the guides as planned, others felt a bit scratchy on entry or exit. The bore looked good. Turns out my handheld hole chamfer gizmo was leaving a micro burr, so I used a small polishing point to dress the edge.
The lifter guides will eventually get bonded into counterbored holes in the crankcase with Loctite. The conical shape is intended to accommodate the ID of the pushrod cover tubes which meet the guides at a mild 3D angle relative to the lifter axis. At this point I’m not really crazy about the metal on metal contact & mitered end. I would prefer some kind of rubberized or silicone material between tube & cone or somehow making a union. The plans call for the tubes being retained in the rocker perch with a small lateral set screw. I have some hopefully better ideas to test but don’t yet have a clear game plan. So, I have deferred this for now & maybe some divine inspiration will occur closer to final assembly. If I have to re-make the guides m, it’s not a big deal.
-
Looking good :praise2: Radial engine cam rings and valve gear looks an interesting topic :thinking:
-
I will discuss the cylinders next. Spoiler alert – in my case it wasn’t quite a straightforward path making 5 cylinders, liners & heads as per drawings in batch mode. I first make some tester parts as per design to get an idea of what was in front of me. This highlighted a few issues where I thought some modifications might be a better way to go. But these 3 components in particular closely integrate with one another, so a design change to one part for whatever reason very likely has a direct knock-on effect to the other parts they mate. I guess we will ultimately see if my decisions were right, wrong or somewhere in between. Overall, I tried to stick to the critical dimensions.
So why the departure from the plans? The cylinder head (to be discussed later) is really the most critical part to have nailed down first because it encompasses many features (read lots of invested machining time). The inlet & exhaust ports are comprised of a smaller diameter gas passage drilled through into the valve cage. And a larger ID counterbore segment, threaded for a steel screw-in fitting which retains the tubing into the head against the counterbore ledge. This threaded style is used in other model engines, including commercial RC engines. Because the port axis is orientated to the head at an oddball angle in top view, the threads of the retention fitting are not initially fully engaged the way they would be like a bolt enters a nut. They must first hook up to a portion of the head thread for a few turns before becoming fully engaged around the port ID. At that point, it’s only a few more turns before the fitting bottoms out, sandwiching the tubing flared end to the counterbore step. No mention was made in the plans of a seal washer at the end of the pipe which I wanted to use particularly for induction pipe, but this would further reducing the engaged thread length. In other words, the design counterbore length is kind of short IMHO. To complicate matters, the heads also have a series of radial cooling fins cut through the port area which further reduces thread contact area. I figured with heat cycles & fuel mung & vibration, it might be asking a lot of these threads. I could select a finer pitch bottoming tap, but I was trying to avoid turning oddball metric threads in my imperial lathe for the matching fittings if possible. As it turns out, some imperial threads might be better candidates. This is a very longwinded way of saying that I really wanted the head to be slightly larger diameter to get more threaded meat in port area.
I modelled the new head in CAD. Everything looked good except aesthetically the head diameter was now extending over the original cylinder top diameter, not as pretty as when they were the same diameter. I’ve seen full size radial examples of both, but I preferred the original look & it solved other issues. So, I changed the cylinder crown diameter, which then meant a different taper angle to end up the same base skirt area dimensions. I also changed the cooling fin thickness & pattern to match my grooving inserts & a more nominal inch spacing pattern. The net change helped provide a bit of cylinder meat for what were shaping up to be slightly thicker liners. More on that later.
-
So, with a new plan in place, on with actual cylinder making. They start out as drops of 6061-T6. I rough drilled them 7/8" in a batch mode. Then each is chucked & machined with most all features to preserve the setup. A boring bar was used to open ID to ~0.005" undersize. Then a 1.0625" reamer passed through so the ID would all be consistent diameter & finish in preparation for the liners.
-
Next was the bring the crown and skirt flange to finish OD & turn the taper portion
-
Next was cutting the cooling fin grooves. I used a 0.043" wide Nikcole insert. They cut like a dream, just keep a bit of cutting fluid on it. Some groove depths are different. The top 3 are a bit shallower to stay clear of the threaded head bolt holes. The next 3 are limited by maximum DOC of the insert ~0.220". Then the remainder grooves are one constant base diameter which then & matches the diameter occurring above the skirt flange. All the edges were lightly chamfered using one of those HSS triangular scraper tools & cleaned up with fine 3M pad. Then parted off.
-
I had one of those machinable expansion arbor blanks handy, so turned the main portion to match the cylinder ID with the bolt lightly engaged & also a raised step datum surface for the cylinder top to rest against. With the cylinder lightly gripped I could face the bottom flange & bring the cylinder to final length.
-
Next, I turned a spacer collar so the chuck jaws could grip the head portion, because at this point the skirt flange is a larger diameter. Using a rotary table, drill & tap the 5 x M3 holes for the head bolts. These holes were then utilized to attach a rectangular fixture plate. The assembly was held in a vise so the flange could be drilled for clearance bolt holes & milled to the rectangular profile. I have a choice to use SHCS, or threaded studs in the crankcase with topside nuts on the flange.
-
Partial assembly pics. BTW, the liners will extend through the cylinders bottoms and that portion is what mates the matching hole in the crankcase
-
Oh wow! A whole lot of things going on in this thread. That’s a very interesting build……. :Love:
Don
-
So now we can see a 'Round Engine' appearing :praise2:
-
this is a great build, very informative, thanks to share this...
on the new design of the cylinder head, I wonder how the threaded fitting will be inserted, as the extremity of the pipe is enlarged in the head and bent in the other extremity, which may hinder the insertion of the threaded ring ?
-
Great work. :ThumbsUp:
Love the machinable expansion arbor blank, had never seen one used before.
-
on the new design of the cylinder head, I wonder how the threaded fitting will be inserted, as the extremity of the pipe is enlarged in the head and bent in the other extremity, which may hinder the insertion of the threaded ring ?
You will see some actual parts pretty soon as I continue to post pictures. But yes, it is a rather delicate balance of accommodating the flared or trumpet shaped tubing end inside the threaded port. Then the threaded fitting must be able to slide over the tubing bend radius. Therefore the fitting length + ID + chamfer must all be sized accordingly. Threaded ports seem straightforward just looking at them, but actually there are a few things going on behind the scenes. Personally I don't care for them much. Next engine I will do what it takes to have bolted flanged tubes. I spent quite bit of time in CAD to see if I could modify the existing design for this, but it got to be a deeper & deeper rabbit hole. Next engine I will mill the outer head profile in rotary table (as opposed to turn it round in the lathe) so that an extending boss for the port can be integrated. Then the fins would also have to be milled on a rotary table.
-
Great work. :ThumbsUp:
Love the machinable expansion arbor blank, had never seen one used before.
Thanks. I was lusting over some expanding ID collets but they are spendy. At least in 5C which i would prefer because I have a set-tru chuck. Other systems you are relying on runout or need to chuck in 4J to dial in. (I'm talking hardened non-machinable collets here of course). The nice thing about the pre-slit blanks is they are turned in-situ prior to mounting work so should be very close to concentric. I have since made a few blanks with a single slit just to see if they can be replicated in the home shop less expensively. They work 'ok'. Ideally they should be turned quite close to ID because a single slit requires more screw torque to open the beak. Maybe a better plan is drill a larger hole traversing the end of the slit. The commercial one is steel with more slits. Theoretically you can keep turning it down for successively smaller jobs.
-
I've made several expanding arbors, drilled/tapped for the screw, counterbored and tapered slightly the end of the hole for the screw head (which was also tapered). Sawed in two slots 90 from each other so it expands out better. Works quite well, used that setup for eccentric followers and such. As you say, you want the OD turned to a close fit on the bore of the part you are holding.
:popcorn: :popcorn: :popcorn:
-
Neat work. :popcorn:
-
Looking good :) :) :) there's a lot of work in those pieces :praise2:
-
It’s coming along very nicely petertha. I’m really starting to think that I need to build a radial someday.
-Bob
-
With all the radials and rotaries being built lately, I too have had the urge to make one. Then I lie down for awhile, and the urge passes. :Lol:
-
Next up are the liners. I should mention upfront that the path I took detoured a bit as things progressed, so the pictures might seem a bit out of sequence without some elaboration. When the CI liners were lapped to final bore & heat shrunk into the aluminum cylinders, the cylinders squeezed back under cooling. The bores reduced to the extent that they needed to be lapped all over again to return them to target dimension. I figured any shrinkage would be quite small, like within a few tenths, thus only requiring a quick lapping correction tweak. But they reduced more like 0.0005-0.0015” & also non-linearly down length of liner. Likely a function of the cylinder’s tapered shape squeezing it differently on the top vs. bottom of liner. Anyways the bottom line is my careful bore finishing work before mating into the cylinders kind of went out the window. I could have opted for something more like a slip fit, but I started to read articles suggesting some liner interference is required to achieve proper heat transfer. And as the engine warms up under running condition, a sliding fit will only get looser yet as the aluminum cylinder expands more than CI liner.
My initial workflow was to first establish the bores of the aluminum cylinders to a consistent diameter & finish, which was brought about by a reamer. It was an imperial size next closest to the nominal metric size specified on the plans. I was already modifying the cylinder barrels as mentioned earlier, so this change was incorporated. This resulted in a slightly thicker liner wall which I thought was fine, maybe even desirable. With the cylinder ID established, I would finish the liner OD to whatever dimension was required for the correct slight interference fit. The interference amount was driven by being able to place the mated liner/cylinder assembly into an oven at moderate soak temperature so that they would release from one another based on the different thermal expansion of the two materials. I’ve done this operation many times on RC engines with my small toaster oven to replace liners.
But let me back up a step. This is my first engine & I was intimidated by making good quality piston rings. This topic has been beaten to death in many other posts, so let’s just say I found myself at the same fork in the road I suspect others have arrived. I was aware of the Trimble ring method documented in Strictly IC magazine. There are also some excellent build posts on this forum where others followed Trimble’s procedures with great results. I find Terry Mayhugh’s (Mayhugh1) build posts on the other forum to be particularly informative. Making the ring fixtures represents some work, but didn’t seem too onerous. But I didn’t have access to heat treating equipment or related experience which seemed pretty important to success. I wanted this engine to run & rings are crucial to success. So, to my thinking, there are 2 main paths:
(A) Bring all liner bores to ‘whatever’ diameter they arrive at, as long as each are identical to one another & appropriate final finish. Using that resultant measured bore as an input value, all of the dimensions to make the ring blanks & heat set fixtures can be determined using Trimble’s equations. The advantage here is that all the liners can proceed along together somewhat as a group. They receive the same tool setup treatment one after another, especially up to the latter stage of finishing where it counts most.
(B) Purchase commercial rings, assuming they can be reliably sourced. This solves the ring making issue. But you need to make the bores exactly the same as the liners they were intended to run in. The O5 is a nominal 24mm bore which happens to be the same as an OS-56 4 stroke engine. Therefore, it seemed like a good idea at the time in my case to purchase 5 rings, including spares for unforeseen replacement. So, I somewhat naively, went down this path. Although it seems like a good plan, in reality it’s actually more work & higher potential for mess up. At least for multi-cylinder engines where the count increases. The issue is the dimensional target – trying to stay within say 0.0001” bore target and simultaneously arriving at that target with the appropriate finish. If the bore is inadvertently exceeded for whatever reason, that’s kind of the end of the trail as it will no longer match the commercial ring. Next engine I will likely go the Trimble route.
When the rings arrived, I measured the cross section against the Trimble values & they were quite closely which is assuring. I also got a new OS-56 liner to closely examine for fit, finish & use as a dedicated glorified bore gage. And added a piston to obtaining corresponding dimensions like ring groove, crown & skirt OD’s etc. to replicate for my pistons. Thus, the shopping list expanded but I figured I could sell the piston & liner as spares one day & recoup some costs. As of today, several years later, they are still sitting in my box. :/
-
So, onto the liners. They start out as drops of 1.25" nominal diameter Class 40 grey cast iron bought from Speedy Metal in USA. They arrive ~1.35" OD I think so you arrive at the good stuff under the skin. Previous to the real liners I also made some testers out of 12L14 & 1144 Stressproof. The 12L14 finishes beautifully but I was a bit concerned about corrosion in methanol fuel environment. The Stressproof machined well, likely a bit stronger & probably a good choice too according to others experience. But sourcing the appropriate diameter was more difficult at the time & sadly 90% of material core ends up in the swarf bin. CI seems to have a reputable track record in conjunction with CI rings. I’m sure wear will be just fine for my occasional running. CI is relatively inexpensive & available in progressive sizes for expected mess ups, so CI it was!
I took a skim cut to get through the crust, faced the end, then pilot drilled 0.375” to 0.875. On my prior testers I experienced a bit of harmonic ringing & minor chatter which I assumed was because I turned the OD to size first & then the bore work. This time I reversed & did the boring first while there was more meat on the wall. Seems to have helped but could also be CI itself vs the prior steel alloys. I found I could hold dimensions quite well as long as one account for any heat buildup. CI is a bit messy so I cover the ways.
-
I used the thickest section boring bar with carbide insert & bored to 0.940” ID. This lands me with 0.005" left to remove for target 0.945" finish bore.
-
I rough turned the main OD slightly oversize, then did the upper liner features. The crown is an extended lip with an undercut so the liner registers onto the cylinder top deck. Then I used some homebrew sanding sticks made from 2" wide MDF boards with wet-o-dry paper bonded with 3M spray adhesive. I found this to be an expedient way to remove the turning grooves & work the material down to size in a controlled manner. The board width spans the entire liner length which helps correct & minimize undulations that can result from traversing a narrower abrasive belt strip back & forth because the dwell time & tension can be different across the length. For reference the OS-56 liner was within a tenth OD all along the surface.
-
The final 0.0010-0.0015" came off with a homebrew OD lapping tool of sorts. This was kind of an experimental venture driven by how much time it took me to achieve acceptable surfaces on my prior test liners. I hoped these generic lapping blanks could be utilized used for this job & future projects if they worked out. Commercial tools are available but they are expensive, especially in larger sizes.
The idea was to have some aluminum blanks cut with the radial pie segment slit pattern you see. Then they could be bored out to the requisite ID & either lap directly on the bored surface, or perhaps in conjunction with a sacrificial split lapping collar to get more utility out of the bore size, kind of like how a collet grips a part. I made a CAD drawing & send it to a waterjet outfit. They cut the slit profile including end holes leaving me to drill & tap for a cross screw for setting lap pressure. I tried different lapping compounds & settled on some cheapo oil based AliExpress diamond paste that comes in a syringe tube.
I guess I could say my lapping tool worked out OK in that any diameter undulations (hilltops) are worked down & the diameter can become quite consistent. But I find lapping to be messy business & best confined to removing small material thickness. It also requires a bit of hand technique like stroke & dwell time & re-charging the lapping goop & fiddling with the clamp tension. Then you have to clean everything spotless, measure at various spots down the length & go at it again. It all takes time. I left the last 0.0005" for 1000 & 1200 paper using my full width backing boards & in all honesty might be just as quick as lapping. Eventually I arrived there. It’s Interesting how CI can get a finish, eh?
-
The skirt ID has a shallow chamfer to provide clearance for the rod motion. One last check of finish dimensions, lightly knock down any corner edges, then part off the liner. Then apply a single layer of protection tape, hold reversed in collet chuck & face the lip surface to final length.
-
Onto finishing the bores. A while back I acquired a Themac tool post grinder (TPG) grinder & played around with it on my previous test liners. I now have mixed feelings about TPG’s. I suppose it suites this kind of application where relatively short length work sticks out of the headstock cantilever mode. Accurate surface dimension & finish combinations can be achieved with the right technique. If the work involves hardened materials, grinding may be the only way to go, but I don’t consider CI to fall in this class. I also had hopes of using TPG for several other applications & that’s where some shortcomings & complications become apparent, especially if the project involves tailstock support. The TPG assembly just wants to occupy the same real estate as TS assembly which really is difficult to work around. I also had a tough time finding suitable wheels, meaning the right diameter & grit & composition combination. I ended up buying a surface grinder wheel from KBC & had a water jet cutter make me a bunch of wheel blanks. I was a bit apprehensive about them blowing up but so far so good. Dumore is another popular name. I can’t speak for their wheel arbors but the Themac has an oddball taper that doesn’t match any common taper, seems to be unique to them. Ultimately, I figured it out, but suffice to say making your own arbors is more work.
Most of the time you will see a TPG lathe setup where people pre-align the lathe compound at a shallow angle & finely increment cross travel depth that way. The magic trig number for convenience is 5.739 degrees compound angle (off of spindle axis) which yields the relationship of 0.001” increment on compound dial equates to 0.0001” of cross bed travel, times 2 equals 0.0002” in bore increment. Just remember that the same rule of removing backlash applies. And this is not exact because unlike a cutting tool, the wheel is slowly eroding in diameter as grinding proceeds. So, you have to measure & re-calibrate more so than other lathe operations.
My compound leadscrew is in pretty good shape. But when I secure the compound dovetail between each pass, the clamping action itself can drift the actual position a bit. I’ve made some improvements to the lock, but it’s still there. So, I don’t completely trust this setup on my machine although I do like the fine incremental feed aspect. Alternatively, I made a fixture to hold a tenth’s reading dial gauge to bear against the end of the cross slide itself which directly measures Y infeed displacement that way. This removes both backlash & table lock issues simultaneously. A sensitive dial gage also acts as a sober indicator of machine vibration which is flowing through to the grinding wheel. The needle fluctuates on either side of the true reading. Ideally, deflection is low & somewhat dependent on where the indicator is mounted & how things are tightened down. I think the TPG is probably approaching the limits of my lathe rigidity & spindle bearing condition. If you don’t have dovetail locks, my opinion is that TPG might be the wrong weapon of choice because once the motor winds up, the sliding surfaces can become ‘buzzy’ & prone to free floating, even with a good quality TPG. A suitable DRO can measure displacement independent of dials so long as you have the right resolution. But consider even typical 0.0005” step increment on DRO display represents 0.001” of bore gone. That’s what made me a believer in a mounted analog indicator. So, after some trials I kind of considered the TPG as a ‘truing’ tool, not a finished bore tool. At least on my lathe & limited experience. That leaves the last thou or more for lapping but TPG is still a time saver. Whether this warrants the expense & setup of TPG is probably another discussion. So, who knows, it may get traded for a TIG welder one day which costs about as much & would see a lot more use in my shop, but that’s another story. What I REALLY need is a Sunnen hone LOL.
Back to liner grinding. I plugged off the back end of my collet chuck so grinding debris would not migrate in behind. I used a single wrap of tape on the liner OD for protection & gripped it in 5C collet chuck.
The wheel was dressed in-situ with a homebrew diamond tool holder. Cover the machine & use a vacuum for this operation please. Then it was a matter of selecting a low spindle RPM, power feed the TPG on low traverse setting & start opening the bore in small ~0.0005” bore increments. It is a somewhat satisfying experience to see partial geometry patches being removed under grinding, meaning non circular sections features you thought were quite true by a boring bar alone. The liner never got warm because of low DOC & more time measuring & futzing. I tried a fluid but t didn seem to be adding any value, the wheel looked clean at these removal rates. The bore finish was ‘ok’ not stunning. The geometry & roughness seemed acceptable but I think it exhibited skip or maybe secondary vibration. I’ve been told my grit selection was too fine, that actually coarser would be better. Grinding is a science in itself. But they popped off pretty quickly. I have been making 6 cylinders, 1 guinea pig & hopefully 5 keepers.
-
TPG grinding examples work in progress
-
At this point I was ready to lap the liners using a brass Acro brand lapping tool and a tenths reading bore gauge. I used my OS-56 liner as a glorified bore gage setting tool.
-
Many hours later of mind-numbing work I had 6 liners to a nice matt finish & within a tenth. And all this was basically a warm up run.
-
Now we arrive at the nasty bit. I put a cylinder in the oven at 450F for a set time & dropped in an ambient liner with no drama. But as mentioned previously, once the assembly cooled, the bore had reduced differentially. About +0.0015” near the top & ~ 0.0005” near the skirt. So not only a significant bore diameter change, but the barrel walls were no longer parallel either. I returned the assembly to the oven & repeated what I’d done a few times already on the tester; heat up & separate to evaluate what was going on. Well, this time even a light love tap after heating was not removing them. This always worked with my test cylinder.
When I carefully remeasured all the cylinders, I had more questions than answers. Maybe because the new cylinder design had more mass. Maybe the reaming was not quite as perfect as I imagined. Maybe the cylinders relaxed a little post-machining because I could measure as much as 0.0005” oval in spots. Or maybe there are micro undulations in the surfaces kind of acting like a screw thread where the mean distance between hill tops is correct, but the surface itself can act like a secondary grip once the shrink has occurred? I decided I wanted these parts separated to be utilized so had to resort to light torch heat. They finally let go. The liner came out a light tan color but amazingly neither seemed worse for wear. They had the same dimensions as when they started out.
-
At this point it was time to weigh my options. I already sunk some effort making the liner OD’s nice & consistent between one another. But the interference just seemed a bit excessive now. It was obviously shrinking the bores quite a bit. Had the liner bores remained unfinished at this stage, it would be of no real consequence, I could have just carried on. I no longer saw much merit pursuing the ability to swap in a replacement liner at some later time because I had already decided to make a complete 6th cylinder assembly spare to just bolt on the crankcase if something bad happened.
I tried mounting my test liner to an offshore expanding arbor held between centers in the lathe to see how easy it would be to somehow lap off a thou in a controlled manner. I’m not sure if I received a Monday arbor but it did not turn concentrically. I put a dial on the OD & it had about 0.002” TIR. I didn’t need more bad geometry problems so abandoned that idea. Glad I didn’t buy a complete arbor set!
So, I bought another Acro brass lap barrel to slightly enlarge the cylinder ID, thus reducing the amount of liner interference & simultaneously tuning up the surface geometry & finish. Hopefully I could use the liners as they were & reduce the amount of subsequent bore correction once shrunk again. Kind of bass-akwards to the original plan but seemed like the best option. This worked quite well. I haven’t lapped aluminum like this before with brass but it yielded a nice light matt finish & the bore gage said it was consistent down the length.
-
Some trial & error futzing, eventually I arrived at combination where the liners could be re-inserted & the bores were undersized in the 0.0005 – 0.0010” range.
-
So once again, the liner bores were re-lapped to target ID, this time as a mated assembly. I will now call these good. I had the bright idea to submerge the assemblies in my ultrasonic cleaner again to remove trace lapping compound. But very shortly thereafter I noticed some corrosion stains starting to form on the liner surface, so I immediately pulled them out. Swabbing & rinsing with mineral spirits is a better way to go. Then a light coat of oil for storage.
Next engine I would leave the liner bores unfinished (undersized) at the boring bar stage. Some of the interference surface conditioning could probably be minimized, particularly if there was no need to pull & replace the liner. The cylinder assembly would now have to be jigged so that the grinding / lapping / honing operation could proceeded on the mated surfaces.
-
That was quite a journey :ThumbsUp: :praise2: :wine1: I do like Acrolaps :) :)
-
Woa - that part of the journey ended up being a lot more winding than anticipated ....
So I hope that you are really satisfied with the result !!!
I think they all look good and should work very nicely on the finished engine.
Per
-
A question came up on the other forum, so pasting reply as further elaboration if my saga verbiage was not quite clear.
I don't think there is an advantage to excessive interference, in fact several potential disadvantages. For example, in my case where the cylinder shape is tapered & thicker wall near the top can contribute to different shrink force on upper vs. lower liner. Pretty much every RC engine I have disassembled requires oven heat to install & remove the liner, even when brand new. My initial heat testing was based on a separate spare test cylinder which was the original design, not my subsequent modified design. But I think either reamed ID surfaces were not as consistent, or possibly they stress relieved a bit. In this kind of application, a half thou one way or another seems to make a big difference. My longwinded story was just to say in hindsight I would not bother grinding & lapping the liner bore until mated to cylinder & completely stabilized. Unless you have good shop methods to very tightly control both OD & ID dimensions & finishes. Jung provides these instructions in his 5-cylinder engine which is probably not far off how mine ended up after lapping the cylinder ID (0.02mm = 0.0008”).
To ensure optimum heat transfer, the cylinder liners must be shrunk into the cylinders. The inner diameter of the cylinder is about 0.02 mm smaller than the respective outer diameter of the liners to unscrew. After uniform heating of the aluminum cylinder by means of gas burner or hot plate (to about 200 ° C), the cold liners are inserted into the cylinder.
-
Carrying on with what surely must be the most drawn out & convoluted engine build post in the history of model engineering, now onto the head assembly. I hope I can accurately recall what I did at the time. Here goes.
I suspect heads are one of the more challenging build aspects of most 4-stroke engines. Maybe because they are the intersection point where so many important & inter-related components must come together. Internally are the valves, valve cages, port passages. Externally the valve spring assembly, rocker assembly, ignition plug, cooling fins, INT/EXH piping connection, mounting holes & fasteners. There is a lot to get right. This is also where many important tolerances, clearances & motions occur.
The reason I mention this is because I tried to stick with the original design intent for the most part, but there were several mods along the way. I pretty much had to make prototypes of most parts beforehand. With heads, a change in one component inevitably has a domino effect to other things. To name a few, the O9 had wider valve seats than what I preferred. So that changed the valve cage, its placement in the head & valve itself. The threaded portion of INT/EXH ports were quite short. Very few threads for tubing couplers which was another motivation to increase the head diameter slightly. Plans are metric & which included tubing sizes I could not get. I found a few (minor) dimensional errors only by transcribing the drawings into 3D CAD. So, what you will see here is more or less the end results for each the various components. Some will also appear out of order construction wise.
-
Here are some CAD assembly pics of where this is going. The heads are made from 2024 aluminum (or was it 6061, sheesh!). First operation was in the lathe. Turning the blank OD, turning a lip boss which fits snugly within the upper liner ID, the hemispherical combustion chamber profile and the radial cooling fins all in one setup. I acquired a used Radii internal/external spherical turning tool which has come in handy, but it’s a bit fiddly to set up. The combustion chamber bowl profile has a specific radius & depth combination which needs to be dimensionally correct to achieve target CR. After turning, the head blank was parted off & finished to length. After several prototypes leading up this point, I made 7 heads ‘production’ heads. 5 for the engine, one as new spare and one sacrificial spare to commence each operation.
-
Next operation was in the mill. I first drilled the 5x clearance hole pattern for M3 hold down screws. One hole occurs at different counterbore depth as a function of head orientation. I made an angle fixture/jig which was used for several subsequent operations as well. Alignment of head to the fixture depends on the combination of the cylinder lip mating the fixture’s center hole and constrained radially by the 5 hold down bolts. Because the heads are in & out of this fixture, this normally may not be an optimal method to align things because of slight bolt/hole clearance. But with all 5 bolts in place & the collective machining deviations, I found they the head didn’t have much if any free movement at all, so called it good.
The glow plug hole, counterbore & thread was done in one operation. Once I figured out how much to offset the hole from the head edge, all the heads were done in one setting. Then remove the head, replace with another, preserve the setting & repeat.
Next was milling the facet faces which become the area to which the rockers boxes are mounted. The valves will exit perpendicular to this face. Once the depth was established, it was just a matter of lopping off the material with a face mill. The fixture allowed me to rotate the head blank 180-deg & repeat left & right side.
-
At this point, I had already made the bronze valve cages and valves in advance so that when it came to drilling the valve cage hole, the target diameter & bore depth plan was fully defined.
I was aware of a few different paths to take when installing valve cages/seats. Some press or shrink the cage into the head with interference fit & valve seat is subsequently profiled. Some strive to have valve/cage sets fully meeting seal test outside of the head (usually by vacuum test), then slip fit the cage into the head Loctite to try & maintain the seal condition as much as possible avoiding any distortion. That was actually my initial plan too, but for unanticipated reasons explained later I ended up doing the seat cutting once in the head. There is only about 0.010” of seat contact chamfer to be removed from the cage lip so it’s not like a lot of material. The risk of course is that if you screw up the seat & cannot get seal or lap your way out of the problem, because the cage would have to be torched out in order to be replaced, hopefully leaving the head in decent shape.
I bored the valve cage hole from the combustion chamber side, out through the top side facet using the same angle fixture, but now inverted. I worked out the required offset enter distance in CAD using the jig edge itself as reference. First a smaller hole was drilled through the head, this mates to the valve guide segment of cage. Then the larger counterbore for the valve chamber body. It was a bit tricky to establish this bore depth because of the curved hemi shape and tool changes. It has to be a flat bottom hole so that when the cage is inserted & bottomed out, the seated valve ends up just beneath a flush position, conforming to the hemi shape as much as possible. For that I undersize predrilled most of the material away and then used a flat bottom end mil to make the hole ID and to target depth, pre-referencing the EM off the fixture as a datum for repeatability
Things went mostly to plan but somewhere between the hole ID, cage OD & surface finish/dimensions I had a few with slightly tighter feeling fit on the cage. Still within the Loctite gap allowance, but mostly I didn’t want to risk having them hang up during glue assembly because bronze triggers accelerate the Loctite cure significantly faster than steel alloys. End mills are not reamers so maybe that should have seen anticipated. Possibly using a boring head might have assisted here, but it seemed like more work & still leaves the issue of a flat bottom hole requirement unless one has an automatic (Wohlhaupter style) head. The end mill was a special order (metric flat bottom) style. In the end I made a simple lapping tool to condition the hole & that worked well.
The cages were glued with Loctite 680 high temp retaining compound. Lastly, I should mention that aside from the Loctite, there is no other mechanical retention of the cages in the head. I did consider pinning them or threading them but I just couldn’t see a good method I could accommodate or successfully pull off with the dimensional constraints. I did a torch test on a dummy assembly & the cage stayed mated, so I guess time will tell.
-
Machining pics
-
The heads & fixture was again flipped to do operations on the facet side of head. The valve hole is first located & centered, then counterbored to accommodate the valve spring body. Then holes drilled & threaded for mounting rocker cages.
A flat fixture was used to hold the head to mill the center groove using a ball EM. Then flipped on its side for sawing the vertical cooling fins which are at various progressive depths. I used a 0.045" slitting saw ~ 0.200" deep about 0.025" DOC per pass. About 200 rpm felt right on 3" OD cutter. I’m still not super confident with this operation. I kept a steady feed rate, used lots of WD-40, cleaned the teeth & trench of swarf between passes because there is very little clearance & aluminum is a gummy material. I've read horror stories where guys folded up the cutter & destroyed the part on the proverbial 'last pass'. At this stage a lot of work has gone into the part.
Lots of edge deburring & cleanup. I use these cheapo rubber abrasives in the Dremel, they work quite well. This pic shows the same tool held in a needle file handle for hand work.
-
The heads at this stage were cleaned & the valve cages installed using Loctite 680 HT retainer. Permanent installation is required at this point because the next step is to cross drill the port passages through the aluminum head & into the bronze cage. As you can see, the valve seats are cut. I will discuss this later on.
-
Fixtures were machined to hold the head in the correct orientation for making the intake & exhaust port passage holes in the lathe. This took some CAD work to figure out the correct orientation & placement. Two 2 separate fixtures were required for intake & exhaust because the offset was different. The fixture was worth it though, my earlier attempts in the mill failed miserably.
-
Watching another air cooled engine come together! Nice job Peter! I'm watching those heads intently!
Dave
-
Once the head was mounted to the fixture, the gas passage hole was spotted & drilled through the side of valve cage. It broke through with no drama, the Loctite joint held. This hole was then opened up with enlarged counterbore & threaded for the tubing retention nut. At this point I already had a prototype coupler nut & flanged tubing prepared to test the fit.
Tapping the 7/16-28 threads was a bit concerning because it enters the head at an angle where only a portion of the hole is getting threaded, maybe 3-4 threads being introduced on one side until the tap starts cutting the entire hole. The threads also encounter interruptions from cooling fin grooves on one site. I held the tap in the tailstock & basically pushed it in along the bed by feel, turning the spindle chuck with the other hand, using only partial chip breaking reversals & lots of cutting fluid. Because the threaded hole is so shallow it required a bottoming tap. I sacrificed another plug tap by grinding the leading threads off & carefully repeating the operation while in the same setup. Single point threading was not a viable option to me.
Overall, I hate these threaded holes even though they are predominant on commercial model engines. They are fussy. The problem is one of scale, it’s more challenging to make typical flanged tubing fittings with smaller yet flange bolts into the head. Especially at some of the entry angles somewhat required with radial engines & their manifolds, not intersecting other holes or features etc. Anyways, I mentioned earlier that I increased the diameter of head slightly from original plans & this was one of the reasons why. Catching just a few full threads on a coupler nut without eventually striping or losing seal or crudding up just didn’t seem appealing, at least from my own RC experience.
-
more related pics
-
This shows the tester head with port completed, exhaust tubing stack & retention nut
-
Sneak peek showing heads essentially done.
-
Valve Cages. As mentioned, the O5 plans originally called for wider valve seats than what I was prepared to adopt. After some forum reading by experienced builders & some experiments of my own with prototype parts, I came to the conclusion that a seat cut face of about 0.010” would be a good target. It would also allow me a bit of wiggle room for installation variation or seat alteration once the cage was permanent in the head. BTW this (thin band) seat dimension was further reinforced by what I saw of model RC engines. This changed the wall thickness of the cage & where the lip occurs within the head in order to keep the valve face somewhat flush & not affect CR too much. The valve length & spring retention features required a bit of modification too. So, some CAD work there.
I used 544 Bronze for the cages. It machines well with sharp tools. I tried a few different ways to make them but eventually landed on this procedure. I turned the outer body OD & stem boss in one setting, parted off & finished to length. I have a Set-Tru 5C collet chuck that grips reliably within about 0.0003-0.0004”. I re-gripped the stock end for end & did all the remaining machining with this setup. Spot, rough drill, re-spot to drill valve stem hole. Then bore the main body ID with a mini carbide boring bar. The edge that would eventually become the valve seat was left at its 90-deg corner.
One issue to note. Bronze can be kind of a grabby material like brass. You want a decent sliding fit on the valve stem, but I think if the hole wanders off track even a tiny bit, that may be a reason for sealing problems that were more difficult to correct. If the valve stem hole is off axis, the valve face will not be square to the cage seat & is dimensionally exaggerated. Seems like it doesn’t take much to make a leaker.
Initially I was drilling the valve stem hole on the first operation before flipping & re-chucking the part. I think that may have been the main culprit. But it could also be related to unequal drill point facets, or maybe reaming the hole, or maybe the operator. Eventually I used a short, stub length carbide parabolic drill on a 120-deg carbide spot drill & results were more consistent. I also eliminated the reaming & just used the appropriate drill size to match the fit of valve stem. In hindsight I also think some of my sliding fits were a bit too close. Perhaps what going on is a slightly looser annular gap allows the axially valve to float just enough to find its way to seating (within limits). We’re talking tenths here but more on this subject later regarding valves.
-
more pics
-
After following some engine builds, primarily by Terry Mayhugh on HMEM forum, I purchased the same 45-deg multi-flute (chambering?) tool from Brownell in USA. I machined a new center pin. One end snugly fits inside the cutter body, the other outboard end acts as a guide, sliding within the valve stem hole of the cage. I practiced making seats on (many) dummy cages when I was getting familiar with vacuum testing & trying different cage designs.
Then an interesting thing happened. I neglected to consider that the protruding lip on underside of head (which fits into the top of cylinder) in combination with the valve angle, would have prevented me from actually cutting the valve seat once the cage was installed. The tool body OD was a bit too big. So, despite my initial plan of cutting the seats after the cages were installed, I was back to cutting the seats before installation, vacuum testing & hoping they would not distort & compromise the seal.
So, my procedure was to paint the valve cage edge with a Sharpie marker along the virgin 90-degree corner, insert the cutting tool into the stem hole. I found it best to hold the assembly upright so only the weight of the cutter is acting on the seat. With a feather light touch, rotate the cutter by hand, kind of backing off at the beginning end of each rotation. There are more than a few ways to mess this up, but pressing too hard is the biggest no-no. If the cut ever starts looking like a superimposed mini sine wave ‘chatter’ pattern, that’s usually a bad thing. The cutter will then start feeding on this pattern & get progressively worse. I have not found a good way to restore it at this point other than using something like the lapping tool to try & flatten the hilltops & start again. The trick is to catch it early, but more ideally, try hard not to do it.
-
lapping tool
-
I made a master testing valve that would be used to validate the new cages, at least as much as possible. It is a regular good valve but with a thin flat relief ground down the length of the stem. The reason for this is to allow bypass of air when vacuum testing the seat once the silicone tube is placed over the top end of cage. The notion here is that if you have a close annular gap between valve stem and hole and maybe lubrication oil, this could yield a false sense of acceptable vacuum leak off time because the annulus itself is acting as a restriction whereas the test is trying to ascertain condition of the valve seat area.
One by one I cut the valve seat on each cage, tested it against the same master valve looking for a lengthy drawdown (ideally a permanent hold) on the vacuum gauge. I also made a valve lapping tool for insurance as shown. The body is made from brass with a steel pin attached with Loctite. The pin is gripped in a collet & 45-deg profile turned. It has some radial slits cut for excess lapping compound. If it starts to show a wear ring, it goes back in the lathe on same setup & re-cut the 45-deg face for fresh geometry. I played with it in test mode and it does work. But it’s not a magic cure for bad geometry.
-
With the valve cages now complete with seats cut, the parts were cleaned spotless with acetone & Q-tips. The cages were installed into the holes with high temp Loctite 680 retaining compound. As mentioned, be aware that bronze/aluminum sets off the cure significantly faster than steel, so bad things can happen if you are not prepared & the part sticks prematurely before landing into final position. Clean up any excess Loctite especially any that gets on the valve seat. After curing the cage seal was retested with the test valve just as a quality check. Then the seats were covered with tape to protect them against more machining & swarf.
-
Lots of very precise well documented work, nicely done!
Dave
-
Thanks all. Apologies for the photo dump. I kept a somewhat steady (snails) building pace, but my posting frequency... not so good.
I'll post the valves next to tie this theme together & hopefully try & maintain a more steady stream hereafter.
-
The valves are made from 7/16" diameter 303 stainless. I made some prior testers from 416 which possibly machines a bit better, but I started to have reservations about corrosion which is bad enough on these methanol burners. Turns out 303 isn't bad at all once you have the right tools, speeds & feeds figured out. My regular go to inserts were ‘just OK’. I wasn’t necessarily after a after a stunning finish but I did want to hit close dimensions & my prior experience was SS does not like to be crept up on. I was ready to try HSS again but landed on this particular DCMT ‘for stainless’ insert. It came from eBay or AliExpress which is always a bit of adventure. Anyways they weren’t expensive & they seem to work quite well.
The stems are 3mm nominal (0.118") for sense of scale. The stock is initially held in 5C chuck & supported on end with my newly acquired Shars slender nose live center.
-
I turned the valve stems aiming for 0.002” oversize. After this I initially tried prepping them with an abrasive block made from MDF & wet/dry paper sized for the full span of the stem. It conditioned it nicely but the paper wears out fast. Subsequently I found with a decent finish & consistent diameter, one can go straight to these simple lapping tools.
The laps are just blocks of steel or aluminum made my sandwiching 2 halves in the vise & drilled through on the centerline with +3mm drills, which ends up a bit oversize nominal & about right for finish lapping. I’ve made a few other homebrew lapping contraptions but these clam shell styles seem to be about as easy as it gets & seem to do the job. Consider them as a disposable item. As you can see, I make a series of lap holes in the tool so as they wear out, I proceed to the next. You can also use the worn/enlarged ones for slightly oversize stock. The split, clamshell feature means it can be applied to the part while in the lathe. I wanted to keep the valve supported in the tailstock for as long as possible which means the waste lump neat the live center is still attached. Whereas other typical lapping tools would require the stem only.
The lapping compound is inexpensive AliExpress diamond paste which cuts very well & washes off readily with thinner. So basically, charge the groove with paste, apply it to the part & just finger clamp pressure go back & forth. It’s very controlled. I think I started with 600# and ended with 1000#. The steel laps were for rouging, the aluminum for finishing. You can get a bit more life out of them as they wear by dressing the flat surfaces on some abrasive paper. That closes the effective diameter, but technically it’s no longer a circle. It's important to have decent tenths reading micrometer & take measurements along the stem. Lapping is messy business so I recommend using gloves & clean often especially your test equipment.
-
more pics
-
I forgot to take a picture making the fillet / trumpet profile, but it was done with a 6mm diameter carbide insert tool taking about 0.010” stepover until it just kisses the stem diameter. The valve is then parted off, flipped & each face trimmed to a defined thickness. In hindsight at this point I should have taken a bit more care finishing the face with abrasive paper or something just for cosmetics.
-
Then I use a 5C collet stop and a split holding fixture to hold the stem. The fixture is slightly larger diameter than the valve head. The stems were trimmed to finished consistent length.
-
The 45-deg valve face is cut with a parting tool corner in shallow passes. I pre-blued the stock with Sharpie. The valve seat profile is complete when there is 0.010" blue remaining relative to valve face. I just held a vernier with jaws opened 0.010" using a magnifier. And now seeing these closeup pictures, my carbide looks chipped which probably didn’t help matters.
-
To finish the valve face, I eventually decided its better to just get it off the lathe. Lathe power isn’t necessary, the cross slide or compound is not being employed, RPM is limited & usually comes with unwanted vibration. So I just held the valve stem in my Dremel (Milwaukee Cordless actually) with a collet & spin it whatever RPM its happy. I figure at this stage, its all about finish albeit controlled by hand, so I’m less concerned by collet or chuck running absolutely true. After doing vacuum pull tests trying different methods, my conclusion was leakage was typically related to the ‘record player’ micro machining ridges on the valve face coming off the lathe. If it vacuum happens to seal first time, I think its more luck than anything else. A polished finish seat stands a much better chance IMO & usually requires no seat lapping usually.
So to achieve that finish, I first blue the seat face with Sharpie & then carefully take the surface down in progressive stages with nice smooth motion, until the machining ridges are completely gone & no more blue appears. Hopefully the pictures provide a sense of this. I start at 1000# - 1200# (blocks with wet-o-dry paper). For final finishing I found these foam backed nail file boards work well, they have 3000# on one side & you can do a lot of valves. Initially I was paranoid of free-handing the faces like this, worrying about round over but its actually quite controlled. You can also re-blue & observe progress.
The vacuum seal success ratio improves dramatically & consistently. Now there may be something else going on & I’ll leave this as an opinion. Even though the polishing is using a backing board and probably only tenths are coming off, there may be some propensity to make the slightest of curvature on the face. This might not actually be a bad thing (within limits) if it means the valve profile can make a continuous seat line even if the stem is off by a teeny degree. Who knows.
-
more pics
-
Last operation is making the groove for the valve spring retainer. I used a Nikole system insert tools which are really nice. Then just chamfer the edge and give it a bit of dressing. I hardened the rockers but the valves are left stock.
-
Glory shot of valves and a few spares. All the soldiers ready for action.
-
This is a great thread and build to follow petertha - lovely work too !!
John
-
Wow! Quite the update Peter! Nice work on the heads, cages and valves! A TON of work! :popcorn: :ThumbsUp: :popcorn:
I really appreciate the detail you give on how you did the polishing/honing work on the valves. That's really interesting.
Kim
-
Not much to say about the valve spring retainers other that they are made from 303 stainless & rather fiddly. I have since what is probably a better machining sequence where it’s made in one setting with the cup side facing out vs 2-step flipping around like I did.
-
The intake & exhaust tubes are retained in the head ports with threaded hex nuts. The tubing end is flared & that is what the nut edge acts on. A Teflon seal washer will reside between the flared end & face of the head port.
The nuts were machined from 0.5" 303 stainless hex. Once the thread OD was brought to size, I made a thread relief groove with Nikcole radius insert of 1.5mm (0.059") diameter. There isn’t a lot of remaining wall thickness on the nut, so I thought this profile might be a bit better than using a square cornered parting type tool. The groove width doesn't offer much error in reaction time to disengage the lathe during threading. I also didn't consider until I got going that the thread point has to terminate in the middle of the circular groove, half the groove width. Not that I have a lot of threading experience but I am reasonably happy with these eBay / AliExpress threading inserts. I was concerned my lathe rpm might be too slow, violating most all guidelines for carbide, but they cut nicely and the insert did not chip.
-
While still set up in threading mode, I also made a solid port plug for sanity testing the actual valves. It’s not a definitive test but I figured if the valve stem is dry (no oil) air might find a way up the annulus & tell me if I had a problem. I installed an O-ring behind the plug to seal, then drew vacuum up the stem annulus. The valves passed at this stage. Later at some point I installed a vacuum line nipple on the plug, blocked off the top of the valve to test the valve seal more directly but not sure I took pictures.
-
The generous chamfer on the outboard side of hole is to accommodate the radius bend in the tubing. May as well toss in some more (preliminary) CAD images showing the general principle. In reality, flaring the tubing is not an exact science & I was fixated on having some kind of sealing element washer between the head face. Maybe not so much for exhaust, but for sure induction. All this takes up space in the port hole & robs precious few threads. So that’s why early on I decided to just increase the head diameter a bit & solve all these issues simultaneously.
-
Fascinating work on the valves and cages :praise2: :ThumbsUp: :wine1: Keeping small bores true and concentric is a problem. On my SU style carb I drilled 2.5mm and then bored out to 3mm using a 2mm endmill as a boring bar.
I made my own seat cutters, a bit like your lapping tool but out of hardened silver steel (drill rod), so they did not interfere with the head.
Loctited cages seem to work well from what I have seen on various builds. The critical area seems to be the section between the port and the seating which is the shortest leakage path.
-
Woa what an update - took quite some time to 'munch through' - very detailed and descriptive :praise2:
I couldn't help wonder - is it supposed to get Airborne later in life ...?
Per :cheers: :cheers: :popcorn:
-
I made my own seat cutters, a bit like your lapping tool but out of hardened silver steel (drill rod), so they did not interfere with the head.
I'd like to see a picture if you haven't already posted somewhere.
-
I couldn't help wonder - is it supposed to get Airborne later in life ...?
It is certainly capable of powering RC model, all the features are there. I am a long time RC guy (pattern/aerobatics, pylon racing, bit of heli, more recently soaring & DLG). But somewhat strangely, don't really have a strong interest in scale. I certainly appreciate them but I'm more interested in the model engineering aspect at least right now. Never say never, but after running success (hopefully) I suspect it will come out for occasional fun fly or show to make noise on a test stand. I've enjoyed this build but it has gone on a long time, I'm getting itchy for the next engine project. Thanks for your interest.
-
This is one of the cutters I made and the cylinder head it was used on.
It is guided on the bore in the cast iron head and there is a separate bronze valve guide.
-
A most intriguing build!
I can't wait to see more of this one.
-
I’ll describe the rocker subassembly next. Probably a familiar theme by now, modifications to some parts require changes to other parts. At this stage when examining more complex assemblies in CAD I kind of adopted a new habit. If something caught by attention, or didn’t look right, or needed later examination in context of another part or a motion, I immediately take a screen grab right then while it’s staring at me, rather than trust my memory or doodle a sketch. I now use this method more often finding it quicker & more reliable. I’m left with a number of snapshot/notes which become the To-Do list for another day. Sometimes a good thing happens where a bunch of seemingly unrelated issues can be resolved simultaneously with one single modification. Hopefully without too much boring detail, I’ll show such images & then onto the end result.
The rocker box is mounted to the angled facet surface of the head with an M3 screw. The inboard base hole straddles the valve with a locating ring boss on the underside. The two vertical members either side in the middle contain the rocker shaft & rocker arm within and snugly fit the inside of rocker covers to laterally retain them in position. The outboard hole in the base faces forward & accommodates the pushrod tube. The result is fully enclosed pushrods and rocker mechanism. The holes for pushrod tubes showed some pesky dimensions on the plans. Drill centers with asymmetrical offset distances & drill angles projected in 2 planes. The angled hole axis make sense of course because the pushrods come through the bottom of the rocker box originating from different positions on the nose case. The intake & exhaust lifters are positioned over their respective cam plates, which are orientated in fore & aft to one another. A longwinded way of saying 2 different rocker boxes are required, one for intake & one for exhaust dictated by these different pushrod holes.
It may not be apparent but the pushrod action is actually slightly 3D, not linear, which is why they are ball ended. The bottom end mates the cam lifters which operate linearly. The top end mates with the rocker arm adjusters rotating through a different plane. The resultant 3D motion has a wider envelope on the top. The point of all this is to say that these motions need to be accommodated without interference of the pushrod within its tube & wide tubes don’t look pretty.
Because of these angles, the pushrod tubes are of slightly different length and need to be mitered differently on either end. On the bottom it mates the lifter bushing. The plans called for as a conical shape bushing to kind of contain the tube at a 3D angle which I initially thought this was a good idea. But I wasn’t particularly fond of how the tubes were retained upstairs in the rocker box. Plans suggested a teeny set screw laterally through the base into a key hole in the (very thin walled) tube. Then there was the issue of wear & tear, engine vibration acting on these small contact areas, oil seepage etc. I knew I would have to deal with these issues eventually but hopefully could defer to when the engine was assembled to this level & things became clearer. I decided to proceed making them, for now omitting the holes. If push came to shove, I would omit the tubes & run open pushrods. But then why have rocker covers with naked pushrods, they kind of go hand in hand. Hey, maybe that’s why many model radials skip this stuff! I’ll return to tubes & lifter bushings later in the story.
-
The rocker boxes were made from 6061 but I probably should have used 2024 because they are kind of dainty parts with lots of holes & loads to support. Five cylinders times two rockers plus spares, call it a dozen. One nice thing about a mini production run is the setup time gets spread to many parts. Hopefully the machining pictures are self-explanatory.
Stock is sized and most of holes drilled. The corners are milled with a round-over EM.
-
The vertical members which hold the rocker shaft are made by band sawing excess material, then milling to final dimension. One vertical gets a tapped hole for a set screw. Partly to prevent the rocker shaft from rotating. Partly as insurance if I decided to omit the rocker covers because the original design presumed the shafts would be captured by them.
-
This shows the rings which get glued into the base with Loctite. They mate into the matching counterbore valve hole in the head so the whole box is retained with a single screw.
-
Here are the fixtures that were ultimately used to drill the pushrod holes through base of rocker box at their correct 3D angle, position & trajectory. One fixture for inlet, a different one for exhaust. I translated the angles in front & side view, then located 3mm hole locations for dowel pins which rest on the vise jaws. From there it was a matter of referencing off of a specific edge & making the hole. Hopefully the picture sequence illustrates this. Pics of making the fixture.
-
Drilling the pushrod tube hole.
-
Testing fit & orientation. I forgot to mention I used K&S aluminum tubing.
-
I knew I would drill & ream the rocker arms all the same (5mm) diameter, so it was a matter of making the rocker shaft OD the proper sliding fit. The shafts (axles?) are made from O1 tool steel. If I didn’t have to mill the flat, I probably could have used a dowel pins & saved some work.
O1 stock arrives as ground finish ~0.001” oversize. But the issue I have found is that it’s often actually a bit elliptical in section, not circular. You can verify this my taking measurements at right angles on the same portion of shaft & can explains why the fit can be elusive. Correcting this took some trial & error on my part.
This shows an alternate technique of reducing/correcting stock diameter to target size & finish, which is a bit faster than slurry/paste lapping. It’s quite controlled & less messy. In about 15 minutes I made a finished stick of stock within a tenth of target dimension & desired finish from which all the shafts were cut. I got the idea by realizing the thickness of wet/dry papers in this 600-1200# finishing range is actually quite consistent across the sheet & even among different papers. Mine average 0.0075", same brand. So, I made a split lapping block which incorporates this paper thickness factored in the hole size as an annular allowance so that when the block is squeezed over the stock with the paper clam-shelling the stock as shown, it bottoms out very near the target diameter.
I milled the lap block from aluminum, then cut in half to yield 2 identical pieces. Clamp together face to face in the vise & drill the oversize hole with closest number drill. Then separate the halves, position both in vise & simultaneously mill off the face allowance from both.
You can spin the stock in the lathe while lapping or just grip it in an electric hand drill. The benefit is the 'tool' never changes shape or wears like lapping paste is employed. Once the wet/dry paper wears, just replace with a fresh piece. Work to progressive finer grit like normal. What’s interesting is you can actually feel a bit of vibration initially which is the irregular, slightly elliptical section. And then it smoothens out as it becomes more circular. Like lapping, it’s not an expedient way of removing too much stock.
Here is the basic design
-
Interesting YouTube link with similar sanding technique.
https://www.youtube.com/watch?v=0clb7aTYn5o
-
Lapping the stock
-
Completed parts including hardening
-
Another Big post and explanaition -> nice parts :praise2:
Per :cheers:
-
:ThumbsUp: nice work….
:cheers:
Don
-
You're making great progress Petertha! :ThumbsUp: :popcorn:
Kim
-
Nice work petertha !
I may have missed it, but what is the purpose of the two small holes in the base of each of the rocker plates? Are they for pins to prevent rotation of the plate on the head, or is that simply prevented by the securing bolt ? Or are they threaded to secure the rocker covers? If not, how are the rocker covers retained?
I really like this 5 cylinder design.
/edit/...I see a CAD model in prior posts showing two retaining screws for the rocker covers that align with these holes
Regards
John
-
/edit/...I see a CAD model in prior posts showing two retaining screws for the rocker covers that align with these holes
You got it John, two M2 screws on either side of the rocker arm secure the rocker covers by threading into the base. I forgot to mention them specifically.
-
Onto the rocker arms. When I machined a prototype from the plans a long time ago now, I figured maybe I messed something up. The contact pad looked just a tiny bit off relative to the valve stem top in closed position and therefore through the opening action. It chocked it up to machinist error(s). But later on, this seemed to be corroborated in the CAD assembly. I’m still not sure, it may be the way it was dimensioned or. I was modifying other shape attributes so just tweaked the contact pad at same time. Rocker arms can have a lot of fiddly radii & transitions, so seems to be a tradeoff keeping the profiles functional & aesthetically pleasing, but also considering the machining steps to yield this result. They always look chunky compared to commercial engines but I suspect some of them are forged. Anyway, the profile allowed me to design machining fixtures.
Some image notes along the way.
-
The rocker arms are made from 0.25" x 0.5" O1 tool steel. I purchased mine from KBC, happened to be Starrett brand. They are ground pretty close to those dimensions which I neglected to mention, I would design around the 0.25” thickness vs trimming to what was quite a close metric dimension. The thought was to harden the valve contact pad area only, presuming I could control the heat & quench in that localized area. Turns out that was wishful thinking with my simple torch method, so the whole arm would be hardened.
The various fixtures are made from aluminum. The O1 stock is both aligned & retained with very close (6-32) clearance holes. Pins might be a better choice alignment wise, but over this length it was sufficiently accurate & simpler with all the repetitive mounting & swapping. Hopefully the machining steps are reasonably clear
Drilling the blanks with requisite holes. I did some design standardization where possible using same drill size and also the holes become the fillet radii between adjoining surfaces. The axle hole is reamed.
-
The valve contact pad radius was profile milled by offsetting the fixture in a rotary table. Just have to be mindful of ending the endmill arc at the right position vs. over-milling into what would be an arm segment. Generally, what I found with O1 on these fiddly parts is saw off as much material so you can do the milling operation in one go at full depth - plunge & profile. If you have to make successive depth passes it increases the odds to mess up & usually the finish suffers. With 0.25” thickness and a good EM it wasn’t a problem. Showing one of the many inexpensive imported rubber abrasives I use for finishing in a Dremel type tool.
-
Similar milling process for the hub to the transition points.
-
Showing the side thinning milling. Required both flat mill & ball end mill to get the profile. I leave the mounting ears on as long as possible.
-
Drill & tap M3 holes for pushrod adjusters.
-
Trim to overall length in the mill vise.
-
A different fixture to do the round over milling for filleted corner.
-
The rocker arms were hand finished with wet/dry paper, rubber abrasives in motor tool & 3M scuff pads. I wish I had the right heat-treating equipment, but I don’t. I used a regular propane torch with the parts positioned into kind of a semi enclosed corner using those beige insulating type fire bricks used in ceramics. Those really help to contain & reflect heat, not to mention make the shop safer. I basically heat to bright orange by eye & then immediately quench in warmed hydraulic oil. I found it basically impossible to magnet test, the low mass means they start cooling quite quickly, so it’s more about having the oil in very close proximity. They cleaned quite easily with 3M abrasive pad & then went into an ex-household mini toaster oven for 20 minutes or so on some tin foil. I think its maximum temperature is ~475F on broil, so whatever hardness number equates to this shade of tan brown is what I am limited to. There were no scale issues, in fact this is how they were ultimately installed into the engine. Overall, I’m pleased with how they came out.
-
Another big effort - but the end result lools amazing in the last pictures :praise2:
Per :cheers:
-
Wow! That's a lot of rocker arms!
Lovely process and great documentation to show us how you did it. Very interesting! :popcorn: :ThumbsUp: :popcorn:
Kim
-
That's a lot of fiddly work to make those rockers individually ! They look so uniform and the blue finish really sets them off against the matt silver aluminium. A great achievement.
I really like your milling jig with the eccentric clamp (brass hex) against the fixed pin. Very clever.
You made reference earlier in one of your cad images to using a 6mm diameter radius tool in the lathe for the thinning operation, but switched to milling only one leg of the rockers (rather than both) . I'm curious to know why you took that path.
Also wondering if you considered machining an "extrusion" profile from which to subsequently cut each rocker off to width.
Very impressive work petertha !!
Regards
John
-
Also, seems such a shame to cover them up! I know, I know...it whats's on the inside that counts....
Regards
John
-
Thanks for the kind words John. The eccentric clamp is an 8-32 MiteeBite. They are pretty good for small fixtures like this. I've also made myself a tooling plate with an XY array of closely spaced threaded holes for general fixturing. A round one for the lathe/rotary table & a square one for mill work. I'll try & find a pic.
https://www.miteebite.com/products/fixture-clamps/
I think my CAD images might be a bit confusing. They are basically snapshots of 'ideas & thoughts along the way' some of which were ultimately discarded, but I probably didn't make that very clear. I started out with the original design with a few minor tweaks. Then an idea to make the side profiling on the lathe vs the mill (abandoned). For a while the contact pad was full width (why? abandoned). A few more iterations incorporating the 0.25" stock thickness & more standardized fillet radii. Here is the the drawing of the final part. Hopefully it resembles the machined ones pictured haha.
If I understand your question correctly, no I didn't really consider making a solid profile from which slabs of rockers were then cut off. The dimensions was influenced by nominal inch thickness O1 stock which comes pre-ground to pretty close tolerance in 0.25" thickness. It happened to be similar (imperial) to metric size called for in O5 design.
-
Thanks for taking the time to address my questions petertha.
What I really liked about the milling jig using the eccentric MighteeBite clamps was that you located the work on the critical pivot point against a fixed pin stop with the eccentric clamp...highly repeatable, and it shows in the uniformity of your collection of finished rockers.
You've understood my loosely phrased questions perfectly, and I really do appreciate your publishing your thought processes into this thread, and support and understand completely the benefits and convenience of using the tooling sizes on hand (drill radii) and stock thickness (01 gauge plate thickness) where they'll work for you. (A trade off of pre-existing ground thickness vs slabbing of the "extrusion" profile method).
This is a great build to follow.
Regards
John
-
I considered making the rocker arm pushrod adjusters from M3 cap screws but unfortunately the dimensions of the socket head didn’t cooperate. So O1 was selected. Basic turning of 4mm stock to 3mm for the threaded portion. I used my offshore die head for threading, put the lathe on low speed, some cutting oil & just fed the die head by hand. Once it gets close to the shoulder just let go & the head spins free on the tailstock shaft. Some finishing with the 600# wet/dry paper bonded flat stick & a rotary tool polishing spider while spinning which does a great job of cleaning the threads.
-
Thread the adjuster into a holding fixture, face the pushrod end to length & 3mm ball EM the socket profile.
-
Into an aluminum fixture to make the 0.025" wide x 0.050" deep screwdriver adjuster slit.
-
I ended up hardening these, the pushrod is stock annealed O1.
-
Back to threading die heads, this kind of prompted me to make some shop-built units which I now prefer. I think my offshore unit is intended to be used with fixed dies as opposed to split adjustable dies, is mostly what I have. My dies invariably fit the import tool very tight which may just be a rectifiable QC issue. I may be getting OCD here, but seems to me that adjusted dies must become slightly non-circular & then they might sit off cutting axis just depending on how they land in the cup.
Also, the retention set screw locations never seem to match the die. I noticed on my import tool that once the screws were landed, the plane of the die itself could get canted off square slightly. Anyway, my new die holder prototype has a looser fit but has set screws on 4 quadrants kind of like a 4-jaw chuck principle, plus 2 more screws at 45-deg to engage the split or fit my other regular dies (pictured) which have a different pattern again. These seem to do a better job on the finer threads. The next best thing would be some kind of floating mechanism like those reamer holders.
-
Nice progress Petertha! And I really like your shop made die holding tools. :popcorn: :ThumbsUp: :popcorn:
Kim
-
The rocker covers are made from 6061 aluminum bar stock. They match the footprint profile of the rocker box base. They are secured with two M2.5 screws which come down on either side of the rocker arm. The internal face of the cover laterally fits snugly to the vertical segments of rocker cage which support the rocker shaft. I made a few minor mods just for ease of machining. The O5 plans show what amounts to a constant thickness shell section, which means internal ball end milling to offset the corner fillet exterior. I cheated a bit by doing a stepped profile in the ceiling area, providing topside clearance but avoiding breakthrough to the reduced width of the external fillet. They still look a bit chunky & mechanical & to my eye. Real ones I’ve seen are often more streamlined but I suspect cast or formed from sheet steel. Methods that might not scale well although I have some ideas on that front for the next engine.
Bring the blocks to dimension using face mill. Drill the hold down screw holes & partial counterbore recess. I tried to save time on certain operations by milling them stacked together, but one has to be careful here (he says from experience). What I mean is if there is even a thou difference in thicknesses; the vise will only tighten on the fattest one & others may come loose which is a bad thing. I’ve have seen setups where soft aluminum wire or some such similar squish-able material is used on one end to take up any slight difference. It all depends on how much material is being removed vs vise contact area. Ultimately, I just took my time & did them individually using vise stops for consistency.
-
The 5mm external radius fillet profile around the top perimeter was milled with a bull nose HSS cutter. This is best done while the block is solid for vise retention. I blued the surface & made some sanity witness lines beforehand. You can in-feed horizontally or vertically but I found setting the datum vertically was a bit easier on this particular cutter. Then progress in from the fixed jaw side until the radius just kisses both witness lines. About 0.050" DOC/pass. Rinse & repeat.
-
The pocket milling was done in a few setups. I’m not sure if this is the right way or not. I find these types of profiles, especially deeper ones, a bit tricky to hit the dimensions & finish simultaneously. End mills can misbehave in confined space surrounded by their own chips. So, first I made a roughing hole on one end to drop the endmill into making an undersized roughing slot. Clearing chips is important or it can make a mess by regrinding its own swarf or sticking to the cutter.
-
With most of the material out of the way, next was finishing the pocket profile to final dimension. I plunge milled what become the internal corner fillets to depth in one go with table locked. Then the perimeter was milled in a few passes to final depth. The same climb mill direction was repeated & I stopped a thou or so before the corner coordinate, otherwise it can get drawn into the stock.
-
The covers were blued again to help with the corner blending from the 3 corner fillet profiles. They were hand profiled using files & finished with rotary tool rubber abrasive wheels. I thought I would be using my carbide burrs for profiling but the technique was evading me. I was always feeling like they wanted to dig in when I wasn’t paying attention. Maybe mine are too coarse or wrong tooth profile.
-
Group shot how they looked at this stage.
-
Nice work!
-
Beautiful parts!
Dave
-
The hand blending and finished items look great !
-
Wow! Those are gorgeous rocker covers! As you said, too bad you have to cover the rockers, but the covers them selves are little works of art, so it makes covering the rockers a little better :Lol:
Kim
-
Looking good :praise2: :praise2:
I made my tappet clearance adjuster screws from hexagon grubscrews cutting the radius for the pushrod with a ballnose carbide endmill. Not the best picture ::)
-
Thanks, I'll have to remember that trick.
-
The link rods were made from 7075-T6 mostly for strength. These do not have bronze bushings on the ends, just the aluminum itself and 2 oil holes. Four link rods are required plus spares.
The stock was milled to correct thickness. Two hold down holes were drilled on either end which aligns to a matching fixture plate. The wristpin & bottom end pin holes were drilled & reamed to size 5mm & 6mm respectively
-
Preserving this same setup, the sides were then milled to shape the dog bone profile. I set my table stops to the start & end points so this could be replicated. This was still my prior RF-45 mill, but I find these stops to be very useful so made the same for my newer mill
-
A center flute was milled using a ball end mill, again using the table stop. Then part flipped to do the other side.
-
The sacrificial ends with the temporary hold down holes were sawn off. The remaining part was relocated to a different fixture, mated to dowel pins corresponding to the wrist pin & bottom pin holes. It was secured with a small strap bar across the middle. This fixture was aligned to my rotary table, actually a tooling plate on top of the rotary table. The masking tape is to keep swarf out. Each end was milled to profile the round over ends.
-
One more fixture to align the part for drilling oil holes on both pin ends. The holes are at an angle to one another, but also slightly offset either side of center to help promote lubrication path.
-
Group shot after some chamfering & finishing.
-
I made a few modifications to the master rod design. Nothing relating to important geometry or dimensions, more cosmetic fillets, profile transitions, tooling availability or where I thought machining steps might be easier. Some dimensions on the plans were a bit confusing to me. So rather than invite a machining error on what is a time-consuming part, I tried to match features to fixtures or jigs at the same time.
I already had developed some prior section views checking for an issue to beware of on radials. That none of rod elements intersect with anything, in particular the link rods with the skirts of cylinder liners. I’ve read about some builds requiring unwelcome notches having to be cut late in the game. Because it’s kind of a 3D problem related to rod length, stroke length & part dimensions rotating & displacing, it may not be easy to visualize. Handy hint if you don’t have a means to detect interference. Do a lateral cross section at the face of the rod section, not through the center (which may falsely show sufficient clearance). It’s usually the corner of the link rod that will contact the bore at first at some angle. In my case, I had to pay attention to the liner bottom chamfer as well as the corner chamfer/radius on the link rods.
-
The master rod was made from 7075 aluminum for strength because it also supports the loads of 4 link rods and some of the cross sections there become pretty skinny. The stock was face milled to thickness as a block. All the holes were drilled and reamed where required in one setting for dimensional accuracy. You can see some holes become the internal fillets profiles between the link rod bottom end pin features. There are 2 small M2 screw holes to secure the crank pin bushing part. So, there is a front & back face to the master rod, otherwise the part is symmetrical.
-
The stock was then reduced to form the main rod section profile. The big end used a larger diameter ball end mill vs. the wrist pin end, then connected by a flat bottom end mill at their tangents. No fixture was required, just a vise stop so the part could be flipped & operation repeated on the other side.
-
The excess material was cut away on the bandsaw. The part was aligned to a fixture using the crank & wrist pin holes & corresponding dowel pins which then set the taper angle of the main rod profile. Then it was just a matter of milling down the stock until it was same depth as the edge face of the fixture (by design). I left the full thickness of stock near on the wristpin hole end for this step so the part could securely gripped vise. The part was flipped in the fixture & operation repeated for the opposite side.
-
The part was blued & link rod profile scribed around the holes using a simple turned profile template of the outer knuckle radius. The part supported in vise jaws by a dowel pin through the link rod hole & excess stock was milled away by eye. At this point I thought I could finish the profile by hand filing using steel guides on either side. This was a bit fussy, at least given my filing skills, so I switched to a milling method using a simple turned fixture held in the rotary table. I didn't want the part to snatch given the way it was clamped & variable excess material, so I stayed about 0.010" outside the radius & crept down on 0.050" increments. The tangent marks were scribed beforehand so e blue so on final pass did the full cleanup. The knuckle OD profile was then milled away full width in one go. I left just a bit of material to be hand blended where the 2 curves meet one another.
-
The master rod has a center slot to accommodates clearance for the link rod bottom ends. I turned a fixture to be used in the rotary table. It mates the crankpin hole with a snug fit & the part is secured by a single screw. I was a bit concerned the part might slip on the fixture rotationally because of the interrupted cutting, so it was re-checked a few times during milling. Fortunately, it stayed put. I have learned not to trust my 3-jaw chuck for things requiring close tolerances & this part qualifies, so the 4-jaw independent chuck was used to dial in the fixture. The part was first datum referenced angularly using 2 link rod pin holes square to the table as shown. From that the recess was rough milled in the center by progressive cutting depths. Then the inside face of the recess was climb milled to final dimension & also meeting the terminal radius fillets on either end.
One thing I failed to consider is that EM’s have a slight corner radius and bottom relief, so slight machining variations show up in the clearance slot depending on its angle & offset position. My upper link rods were binding a bit until I realized what was going on. The bluing makes it look worse but it took some careful hand filing & scraping to get the inside corner sharp without mucking up the faces. So, I recommend having the link rods done first or at least a representative tester.
-
The wrist pin round over profile was similarly done by bluing & milling & finishing using steel guides.
-
The oil passage holes were drilled into the wrist pin hole. During fitting, if any final lapping was required on holes, usually more related to de-burring, these Acro-Lap tools worked well.
-
The link rod pins were made from O1 drill rod. Other than being center drilled through, similar method of lapping them to dimension using the wet dry abrasive paper method. They were hardened as well although I’m not sure it’s required running in aluminum. The trick is they have to be a nice sliding fit within the link rod, but also a reasonably snug fit within the mater rod. So, you have to kind of pick specific your specific reamer.
-
The master rod bushing is made from bearing bronze. Straightforward turning other than the features are quite thin. It has the proper sliding fit on the crankpin OD and also has a face flange feature between the master rod body & the crankshaft pin area. This was v1, I ended up making another v2 during final assembly with some tweaked dimensions to manage the clearances.
-
Some shots of the master rod & link rod assembly at this stage.
-
Wow! That's beautiful work, Petertha! :popcorn: :ThumbsUp: :popcorn:
Kim
-
Lovely finish on the master rod (and all of your parts) for a component with so many tangential features! The thought you've put into your work holding and machining sequence certainly shows in the finished pieces.
And a clever design with the master rod bushing flange retaining the link rod pins on one side, minimising both the overall thickness of the assembly, and the machining requirements for the link pins.
Very impressive workmanship petertha!
Regards
John
-
Thank you for showing the whole sequence :ThumbsUp:
And like John - I love the details that sequre the pins :Love:
The whole Master + Slave Rod assembly looks really great :praise2:
Per :cheers:
-
Such a wonderful assembly of extremely well made parts. Beautiful work!
-
Wow, gorgeous work.
-
Thanks for the nice compliments. I must admit, the master rod assembly felt like a bit of milestone. Its kind of the heart of a radial engine. I'll keep working on the next chapters.
-
The pistons were made from 7075 aluminum. I mentioned earlier in the build post that I decided from the onset to use commercial piston rings for the O5 as opposed to making my own. I wasn’t sure I would be up to the task of rings on a first engine build. Maybe not so much machining the rings & fixtures, but doing the proper treating for the gap because I don’t have an oven & wasn’t quite sure about using a torch. I wanted to provide the engine the best chance to run, so this seemed logical at the time given all the other variables of engine building. As mentioned during liner making, buying the rings might be kind of false logic, or at least on a multi-cylinder engine, because it thereby requires you to make each cylinder bore identical to one another, to a correct dimension within tenths and to a correct finish, 5 times plus spare(s). Collectively, I think is more work & more challenging.
The O5 bore is essentially the same as an OS 56 4-stroke (0.56 CI). So along with the rings I also I purchased a single piston to replicate the ring grove dimensions and slight diameter reduction around the crown. Picture shows the commercial die cast? piston alongside my tester blank. Also of interest, the OS piston ring dimensions & open gap with is pretty much bang on what Trimble method works out to. The pistons are 0.0025" undersized to liner so just requires careful finishing & measuring using the same micrometer.
-
The ring groove was cut using an undersized Nikcole grooving tool. I set up a tenth’s indicator on the carriage to better monitor carriage displacement. The width was verified with a feeler gauge stack matched to the O.S. piston. The inner diameter (depth of ring groove) was measured with blade micrometer.
-
The piston blank was parted off oversize, flipped & trimmed to length. I used tape to protect the finish from the collet.
-
The 5mm wristpin holes were drilled & reamed while the blank was still solid. On my initial tester, I drilled the hole after internal material was removed, but I didn’t like the feel of the drilling through the wall, breaking out in the middle & continuing the hole through to the other side. I couldn't actually measure out-of-square but just preferred this solid method, basically pecking 0.050", clear chips & repeat.
-
Re-chuck the pistons back in the lathe to drill a 0.375” pilot hole to remove material & counterbore the skirt ID.
-
I made a mill clamp fixture to hold the piston orientated to a dummy wrist pin dowel. Then the rod clearance slot was milled away.
-
The non critical edges were lightly deburred with rubber abrasive, part cleaned & dimensions confirmed. I installed a ring to do a test fit in a lightly oiled liner. Insertion & movement felt about right and the ring gap seemed the same as the commercial assembly.
-
The wrist pins were made from O1 drill rod, brought to diameter using the sandpaper lapping block method previously described. I reamed the piston and rod holes the same diameter so the piston fit was a snug sliding fit. And I lapped the rod hole using super fine compound just slightly to what I thought felt like a close running fit. The rods always seemed to require a bit touch up after drilling the oil bleed holes (internal burr?). The wristpins are solid but each end is drilled slightly to accept aluminum pads on either end intended to wear vs scratch the liner bore should the wristpin drift. I have seen Teflon pads used in commercial engines but I didn’t have the right material & was less confident of how to retain them.
-
I hardened the wristpins using torch method. I’m not sure hardening is required because they run inside aluminum.
-
The aluminum end pads had a little bleed hole drilled through which I learned the hard way is required, otherwise they can ‘hydraulic’ when the Loctite is applied & can set up in an incorrect position. I left the diameters slightly oversize so that once bonded, they get blended to the pin diameter, chamfered & finish length in one lathe operation.
-
Assembly pics
-
Wow, very tidy work, Petertha! :ThumbsUp: :popcorn:
Kim
-
Nice work petertha!
Looks like the 7075 machines very crisply (particularly the milled pockets), without pickup on the tool.
Consistent tiny chamfers and your deburring methods leave a wonderful level of finish.
John
-
The aluminum end pads had a little bleed hole drilled through which I learned the hard way is required, otherwise they can ‘hydraulic’ when the Loctite is applied & can set up in an incorrect position. I left the diameters slightly oversize so that once bonded, they get blended to the pin diameter, chamfered & finish length in one lathe operation.
Oh that little trick is getting filed away for the 917.. Nice work Pethetha!
Dave
-
Next up is the intake manifold assembly. Hopefully this topic won’t put many of you to sleep. After making the components according to plans, some issues came to light and & I ended up adapting things a bit differently. Maybe some of the modifications & reasons behind them will also be of interest to those contemplating a similar build.
The manifold part is bolted to the rear of the crankcase using 10x M3 screws. The forward-facing section is basically a lip machined to fit snugly inside the crankcase housing ID. It also incorporates an O-ring for seal which I noticed was not featured on the O9 radial. The middle flange section has 5x M4 threaded holes for motor mount standoffs to connect the engine to the firewall. The rear section is the manifold where the intake tubes tie into & carb is mounted into.
On each intake stroke, fuel mist is drawn through the carb, into the manifold’s center hole, into the crankcase chamber (red dots). Because oil is premixed with the methanol fuel, the intake mist lubricates the components within the crankcase before carrying on to the heads. This is typical RC engine style lubrication. Fuel mist exits rearward from the crankcase, out through one of the 5 manifold holes (orange dots) through its respective intake tube into the head’s intake port.
If you recall earlier in the build description, the plans call for the nose case chamber to be partially filled with an oil bath to splash lubricate the front-end components, the cam plates, cam bearings, lifters & planetary gear train. In other words, a separate lubrication system to the rear crankcase mist flow. After much indecision & hand wringing on this issue, I decided not go this route for now. Rather, I opened up the front gear plate with an array of apertures (holes) working around the existing idler gear & bearing layout. So, I’m depending on the same incoming mist to carry on further forward into the nose case & also lubricate the nose case jewelry.
From what I can tell, this mode is similar to other methanol glow radials such as Jung designs, commercial engines like OS & Saito, possibly others. I do feel there is a bit of risk here because the crankshaft counterweight & master/link rod assembly blank out a healthy percentage of open flow area apertures & the O5 seems a bit more crowded compared to these engines. If my decision turns out to be a lubrication fail, hopefully damage will be something short of catastrophic & I will have to revert to a nose case oil bath.
-
The O5 plans called for the same flow nozzles prescribed on O9 radial. They are basically profiled rings, inserted into the 5 front facing port holes & retained with Loctite. Maybe I'm wrong but aside from a bit of standoff distance from the center carb port & a slightly curved leading-edge profile, I didn’t really much advantage given the turbulent gas flow & long tortuous route each intake charge takes toward the head.
-
For parallel interest I attached a picture of the OS-FR5-300 radial manifold showing spiral flow path grooves milled in the manifold. It seems by the article description that the incoming fuel charge is sealed off from entering the crankcase. It flows directly from carb into each spiral groove into intake tube. So, no mist lubrication to rod components? The Edwards radial is a similar, even simpler gas distribution box flowing from carb to tube, but it has an independent oil pump system. The OS-FR7-420, possibly a later engine, shows what appears as vane pump somehow driven off the crank. I’m not sure the pressure boost could be very high but it must be there for a reason. But again, sealed off from crankcase. If anyone has more insight to these OS engines I’d like to hear. I’ve seen similar vane pumps on other radials like this Whirlwind.
-
The carb is integrated directly into the rear section of the manifold boss, counterbored to match the throat OD & length, so that’s how I machined it. I suspect the intent is for a compactness, keeping the carb assembly within the motor mount standoffs, forward of the firewall.
Around this same time, I realized I probably made an error with my carb choice. It was for a 2-stroke 0.40 CI glow engine but the venturi hole appeared rather big. This led me to a more detailed review of carb sizing for 4-stroke glow engines which I have posted elsewhere on the forum. This confirmed I was probably wanting a smaller orifice, especially where idling & transition was preferred over top end. I started looking at options from RC suppliers. Getting them was easy enough but it turns out that their throat bodies come in a multitude of dimensions. Sleeving the existing manifold bore and/or the orifice was do-able but not a great option. I ordered some candidate carbs & moved onto the next issue.
-
The plans show the intake tubes tying into the manifold boss via aluminum ring fittings which are grooved to hold a captive O-ring for gas seal. The fittings are permanently Loctite glued into counterbored holes of the manifold & these holes connect to the axial flow passages. Here I ran into some assembly problems. The specified tubing was (metric) 8mm OD aluminum. I found some sticks from an RC supplier but bending the pipe was not pretty. This is a subject unto itself, usually involving filling the tubes with a filler alloy or material. But I acquired some aluminum 5/16” OD Versatube from Aircraft Spruce which is dimensionally very close. There was no problem bending this with my hand tool. The bigger issue was straightening out the coil as it was shipped, but I have since found some shop made solutions which I will add to the to-do list. The initial tester parts were coming out semi-promising but more refinement still required.
On the ring fittings I tried a few different O-ring sizes, durometers, materials & O-ring cut depths which gave varying degrees of seal against the tube (or not). I’m trying to mitigate any chance of air leak across the O-ring because it would adversely affect fuel mixture & cause running problems. The ring fittings were proving to be quite fussy & it wasn’t going well. I didn’t want to resort to silicone adhesives because I expect the engine would be knocked down & assembled many times.
Another issue was with the assembly itself. The tube end first has spud into the O-ring fitting but is limited by a shallow depth. The tube has to have sufficient wiggle room to then position the flanged tube end into the head & secure with nut. If the pipe bend profile or cut length was off just slightly, one or both ends did not fit well in my opinion. I was paranoid of stripping the fussy threads in the head which enter the head at an angle & partially cut across cooling fins. So, I abandoned the O-ring fitting idea & made some short extended ‘stack’ fittings to go into the counterbores. The idea was to couple the stacks to the tubes using a short segment of flexible tubing. Not as pretty, but seemed more functional & hey, big engines do it too!
-
I’ll detail the intake tube making separately, but at this point I was getting the hang of making somewhat plausible tubes from a straight>curve>straight layout pattern. I could bend the radius, form the trumpet end to the head & mostly land somewhere near the manifold stack segment. What I wasn’t thrilled about was the overall look & fit of the pipes. It was quite evident that the tubing axis was kinked where it met the manifold mini stacks. Another indication was the tube ends needed to be mitered to line up. This geometry issue was probably the root of my original problems using the O-ring fittings. The segment of flexible coupler disguised some of the sins, but it just wasn’t pretty. I could have called them functional & moved on, but…
-
I spent some time in CAD with the assembly & it slowly became evident what was going on. Not to bore you with details but because my 5/16” tubing bender tool was constrained to a single, defined radius, there was no geometric solution that would satisfy the tube axis coming off the head port angle, around a radius & ultimately intersect the existing manifold port holes in their existing location/orientation using any combination of straight + curve segment lengths in a 2D plane. I could make it work by either a more complicated 3D bend sequence or a specific bend radius that was smaller than my bender tool.
-
So, my options appeared to be 1) make a general-purpose tube bending tool assembly to facilitate different diameter forming dies in order to bend the required radius 2) use my existing bend tool & make a new manifold that would accept this fixed bend radius. I did some reading on shop make bending tools. Eventually I want to make one, but for now, moving forward with a new manifold seemed worth a shot. This would also allow me to tweak the other issues - generic adapter plate for different carbs, eliminate the crankcase O-ring & just replace with a sheet gasket & skip the flow nozzles & just chamfer each hole.
The net effect was a mixed blessing. To solve the geometry issue using a straight-curve-straight recipe and bend radius all in a 2D plane, the tubes needed to enter the manifold at a steeper, oddball angle as opposed to the original design which was a simpler radial spoke pattern. The manifold boss itself also needed to be a bit longer, but that was of no consequence. It also required shifting the M4 mounting studs to some degree. And one set of M3 screws were a little less accessible which I didn’t even consider until the part was machined. So, in hindsight maybe a new tube bender may have been a smarter choice but it is what it is for now. Next radial I will be wiser on these issues.
-
Some machining pictures of the new manifold
-
Some machining pictures of the new manifold
-
Some machining pictures of the new carb adapter.
-
Nice work on the redesign and tube bending petertha.
Your solid model cad illustrations of your design rationale is thoroughly engaging.
Regards
John
-
Lot's of nice work there, and some good logical decision making. The intake tubes look great. :ThumbsUp: :ThumbsUp:
-
Once again Beautiful work, Parts + great explanations :praise2:
The OS-FR7-420, possibly a later engine, shows what appears as vane pump somehow driven off the crank. I’m not sure the pressure boost could be very high but it must be there for a reason. But again, sealed off from crankcase. If anyone has more insight to these OS engines I’d like to hear. I’ve seen similar vane pumps on other radials like this Whirlwind.
I believe that all this has been debated in Mikes Bristol build here on site .... but it boils down to better fuel mix, with a more even distribution -> all cylinders get the same quality Air/Fuel Mix.
The later OS Engines uses a 'Recycle Oiling System' .... Here the 'Blow-by Oil' that makes it past the pistons, oils the content of the Crankcase. Since a Four-Stroke normally always has a positive pressure inside - this forces the oil out through the Cam-Gear bearings, lubes the Cams + Followers. Here the is a small 'nick'/bypass, that allows the oil to continue up the Pushrod Tubes -> Lubrication of the Rockers and Valves .... And now the Final smart detail - a tiny hole / Oil-passage back into the Inlet (before the Valve), where the Oil is sucked back into the Combustion Chamber, during the Intake Stroke :insane: :praise2:
I think there is a good chance that the Mist is enough to oil your Engine - as the Pressure fluctuations in the Crankcase, also transfer some in and out of the Front-Housing …. It will not be huge, but the Gears + Bearings don’t require much ….
Best wishes :cheers: :popcorn: :cheers:
Per
-
The tool I purchased to make the curve segment for both the intake tubes & exhaust stacks was a Ridgid Instrument Bender model #36092 for 5/16” tubing. It has a bend radius of 15/16” (~0.934” or ~24mm) which is a fixed dimension as a function of the die head. It worked quite well for this particular job. The only downside for general model engineering is each tubing diameter requires a corresponding tool which in turn has its own minimum radius. They are not exactly cheap & also limited to 180-deg curve if that’s an issue. So, a future project for me will be a shop made bender tool where I can vary the die diameter and if possible, somehow do 3D profiles
The intake tubes were made from a product called 3003 Versatube purchased from Aircraft Spruce, 5/16” OD x 0.035” wall thickness. This size reasonably matched the metric 8mm diameter called for in the plans. The big incentive for this material was that bending was not really difficult, no internal support filler like Cerrobend was required & they kept a pretty uniform circular section with no kinks. About the only thing I would do different is invest in making a tube straightener device from roller bearings because the tubing comes shipped in ~12” coil, so straightening it out beforehand to lay out my straight > bend > straight profile. I basically cut a longer working section, carefully un-bent I by hand & then rolled it on a hard flat surface. There are some YouTube videos that do a better job describing the roller devices. The exhaust stacks were made the same way except from copper alloy auto brake tubing which I thought would be better for exhaust heat. They were just simple 90-deg bends only.
https://www.ridgid.com/us/en/400-series-instrument-benders
https://www.aircraftspruce.ca/catalog/mepages/3003versatube.php?clickkey=17152
-
Using a pattern drawing, I marked out roughly where the bend section would occur first, leaving excess straight material on both the head end & manifold end to be trimmed later. The operation was set the lock & bend the tube X degrees to a mark. There is minor spring so just a bit of trial & error.
-
For the head end, I referenced a line on the straight segment & attached my steel shop made flaring tool. It’s basically a split die that lightly grips the tubing so the trumpet can be formed by screwing in a chamfered shaped profile die. I ended up threading the die hole & then bored most of the threads off so the remaining serrations it would provide enough grip to the tube, hopefully without too much resulting bite marring. Without these ‘teeth’ I found the tube could slip during the trumpet forming. Maybe this could have been mitigated with Cerrobend or some kind of plug material. I cut the tubing slightly longer than the face of the flare tool & used a ~1/32” thick aircraft plywood template as a guide to flush file the end. This was to allow the right amount of material to be flared, determined by trial & error. The flare profile is necessary for the head port nut to tighten against.
-
Then it as just a matter of squeezing the flare die into the tube until the bolt was tight. I dressed the tubing face flat using the tool itself as a sanding guide.
-
Once disassembled from the tool, some cleanup work to remove the grip marks & profile the end. The trumpet flat will reside against a Teflon washer seal in the head port counterbore.
-
With the tube loosely tightened into the head against the seal washer, I was able pivot the tube until it approached the stack tube from the manifold & make a mark indicating where to cut to. With a bit of coaxing, they eventually lined up.
-
The installation plan is: first push a section of silicone tubing completely over the end of intake tube, swivel the tube aligned over the manifold stack, then push the hose down so its centered over the joint. Not quite sure about hose clamps at this point. I thought I could modify these automotive wire clamps by snipping the bowtie, but I’ll try & think of something more fitting.
-
Basically, the same procedure for exhaust pipes. They are made from 5/16” OD auto brake line. A little bit heavier wall than the intake tubes but the bender had no problems.
-
At some point I may consider a ring exhaust collector that these short pipes would tie into. But at present I lack the tools & know how. Something to aspire to!
-
Lovely Pipes :ThumbsUp: + great match :praise2:
I'm not sure that you need any 'Clips on the silicone Tubing' to keep them in place ....
But if you do - some one here has designed a nice little 'Wire-Bender' - that gives you an authentic looking locking wire around the Tubing.
Per :cheers:
-
Vixen's got a How-To here.
https://www.modelenginemaker.com/index.php/topic,10381.msg237228.html#msg237228 (https://www.modelenginemaker.com/index.php/topic,10381.msg237228.html#msg237228)
-
Thanks for tips. Yes I've seen that method & miniaturized tool. Very scale & professional looking.
-
Before I get on with the pushrod tubes, I’ll back up a step to revisit the bronze lifter/tappet guides because they relate to one another. The plans show a conical profile guide bushing. The idea is to accommodate the pushrod tubes approaching at a 3D angle dictated by the angle/stagger viewed from the front & the different fore/aft position viewed from the side as a function of the intake/exhaust cam plates. The cone also serves to hold them captive. The bushings themselves are inserted into the nose case with Loctite.
-
When I did some test fitting, the fit of the tube to the cone was reasonably OK with some mitering, but I wasn’t keen about metal on metal. Not so much leaking any residue oil, but the metal on metal of a thin wall under normal engine vibration. And then the way the pushrod tubes were to pinned into the base of the rocker box part with a M2 setscrew & a teeny hole into the tube wall to maintain orientation was looking increasingly finicky to my eye. I tried some ideas like heat shrinking the cone. An alternate bull nosed guide to put some kind of disposable tubing boot over the end. Nothing jumped out as a great solution. Note to self, heat shrink is amazingly difficult to stick to metal without some kind of added adhesive. I suppose nothing to fuse like typical sheathing?
-
This ultimately led me to what you see here. I made a new bushing that has 2 captive O-rings. The lower one is a bit wider & thicker; it acts as a snub for the tubing to bottom out on. The upper O-ring self-centers & seals against the tubing ID. After fiddling around with different tubing sizes, I settled on one particular size from the K&S dispenser at my local hobby shop. I’m sure it’s been there from the 80’s so I cleaned him out. Remembering that bronze sets up fast in aluminum, it was Loctite time. Next engine I would make these screw-in or something like that for easier replacement. I’ll show how the upper end of the pushrod tube was similarly O-ringed so the end result is that its captive between rubber on both ends.
-
When I did some test fitting, the fit of the tube to the cone was reasonably OK with some mitering, but I wasn’t keen about metal on metal. Not so much leaking any residue oil, but the metal on metal of a thin wall under normal engine vibration. And then the way the pushrod tubes were to pinned into the base of the rocker box part with a M2 setscrew & a teeny hole into the tube wall to maintain orientation was looking increasingly finicky to my eye. I tried some ideas like heat shrinking the cone. An alternate bull nosed guide to put some kind of disposable tubing boot over the end. Nothing jumped out as a great solution. Note to self, heat shrink is amazingly difficult to stick to metal without some kind of added adhesive. I suppose nothing to fuse like typical sheathing?
Hello petertha
Try ATEM adhesive Lined heatshrink tubing
Mike
-
The double Oring looks like a neat solution.
-
Try ATEM adhesive Lined heatshrink tubing
Mike
Aha! Thanks Mike, I will look into that product, I can envision other uses.
I tried everything in my heat shrink arsenal. It didn't stick well & I could envision only getting worse with running heat & oil. The best I managed was a light coat of urethane adhesive (shoe goo), heat set to conform. But it bonded too well & a bugger to remove the remnants so not viable for likely frequent reassembly. Silicone tube had sufficient grip & bend as a makeshift boot, but even the thinnest wall thickness I still looked out of place. (Medium allergic reaction to Model Scale-A-Tosis). And no, yellow was not the color of choice, just what I had on hand.
-
With the new bronze lifter guides now permanently inserted to the nose case, I made the pushrod tubes. First step is mitering the bottom angle, initially by trial & error. As mentioned, the exhaust tubes are slightly different 3D angle than intake tubes, hence my exotic color scheme. Once my belt sander table & protractor guide was set, then rinse & repeat all the tubes plus spares. With the tubes resting on the bottom bushing O-ring & threaded into a rocker box, rough cut to length with a jewelers saw.
Then I assembled the appropriate coupler fitting on the tube along with the top O-ring, applied some retainer glue to the joint area, then pushed the coupler upward so it had the right amount of compression squeeze. I used some makeshift clothespin clamps until glue cured. The finished tubes seem to sufficiently maintain orientation rotationally because of the coupler miter angle kind of self corrects. Then I carefully filed & finished the tube top to match the rocker box base plus a bit & confirmed the pushrod action functioned without any interference.
-
more pics
-
The pushrod collars were first drilled, OD turned & parted to rough length. I worked out a milling fixture which would hold them at the appropriate rocker miter angle by using dowel pins in the end. One position for the intake, the other for exhaust. I glued the collar stubs into counterbored holes with a fillet of support epoxy. Then milled across them all to a depth offset from the to surface of fixture. Then I heated fixture with torch until the epoxy turns a tan color, gets rubbery & releases. Most of the glue comes off easily but I used the spiral wheel to clean them up.
-
The same fixture can be re-used for multiple part runs after some cleanup. This shows how the upper O-ring fits the underside of rocker box.
-
Lovely attention to details :ThumbsUp: and it Shows :praise2:
I know that you still have some to go, on this build - but certainly one of those I look forward to see a Video off it running :cheers: :popcorn: :cheers:
Per
-
Thanks Per. I'm slowly making my way through my build pics & descriptions. Hopefully the smoke & thunder video to follow shortly thereafter.
-
While on the general topic of marrying pushrod tubes to bushings or rocker boxes, I thought I would mention my side effort attempting to mold my own boot. I think that’s what they are called? It wasn’t exactly successful, partly because of the finicky size & what I was trying to achieve. But I’ve always wanted to cast silicone parts from aluminum molds so might be worth showing this for similar applications which may arise on our model engines.
Full size engines obviously have the same issue of pushrods entering their housings at oddball 3D angles. Some shallow, some quite steep. I’ve seen opposed cylinder engines with kind of accordion profile on the ends I assume for this reason. I could not envision any easy way to make this.
-
Specific to radials, I’ve seen variations of an external rubber boot. I’m not sure if it they are custom molded or segments of straight tubing just deflecting under submission. I tried a silicone tubing cutoff as mentioned. But it was rather thick wall thickness & still didn’t offer me any kind of rubberized gasketing effect under the metal tube, although I thought about positioning an O-ring in there.
-
I thought if I could make a common silicone coupler part with a small internal, integral ledge for the tubing to reside on, it could be used for both the upper & lower ends just by cutting the ends angled to suite. The mold turned from aluminum. The silicone is a low durometer product. Supposedly no degassing or pressurizing required, but I’m a bit suspicious of that. I bought some black color tint & you can see the results. I used the recommended release product but it parted very easily. I can see this stuff being useful for other modelling applications for sure. Silicone is good as an electrical insulator & impervious to methanol & oil (but I didn’t test gasoline).
https://sculpturesupply.com/products/mold-max-29nv?_pos=1&_sid=772b2515a&_ss=r
-
But for my purposes… Meh. It was kind of a small finicky part to learn on. I guess I could call it a technical success but didn’t like the look of it in the end.
-
Good progress :praise2: :praise2: I'm sure you will find a suitable solution to sealing the induction pipes and pushrod tubes :ThumbsUp:
-
I continue to check in on this build from time to time, and amazed at the progress and quality of work each time. Keep it up Peter! :popcorn:
-
Hello petertha
Try ATEM adhesive lined heatshrink tubing
Mike
Have you tried it yet?
Mike
-
Hi Mike. No have not landed a specific brand that uses that acronym, but in all honesty I haven't pursued it too hard. Digikey is a pretty big supplier I can get things from. They have some good cross tabulations including material type & other parameters but not adhesive specifically. Is there something in this list that pops up as similar? I'm sure I've stumbled on it elsewhere.
Just to be clear to all, this isn't holding up the show. My double O-ring tappet bushing & captive upper O-ring beneath the rocker cage is a viable solution, so what I ran with. Its just that shrinking tubing over metal might come in handy for other purposes down the road, so a good trick to have in the arsenal.
https://www.digikey.ca/en/products/filter/heat-shrink-tubing/483
-
Hello Peter,
I was sure you had developed your o-ring seal arrangement sufficiently to run with.
The adhesive lined heat shrink tubing idea was only offered as an alternative, a quick fix. ATEM is only one brand, there are many others available, it's prime role is in waterproofing cable joints. Just search for "adhesive lined heat shrink tubing" on e-bay or even Amazon and you will find a wide choice of manufactures. As you said, a useful material with many potential uses.
Mike
-
On the Digi-Key site, you put a mark in the "In Stock Box" and then scroll to the right to fin the "Feature Window" and select the over all type - Adhesive, Chemical etc.
I loved both your O-ring and Rubber-boot solution and I'm confident that you will find a satisfatory solution Peter :ThumbsUp:
Per :cheers:
-
The pushrods were pretty simple to make so only one picture to share. I used 2mm diameter O1 tool steel only because it was easy to obtain in metric & I wasn’t quite sure if either end would be hardened. The cam followers are hardened but not the rocker adjuster screws, so we will see. The diameter did matter because the pushrods make a 3D motion inside the tubes & according to my CAD drawings, come close to the edge of the tube wall at certain maximum deflection positions. I could go a little it bigger diameter but not much. The intake & exhaust pushrods are different lengths owing to fore/aft cam plate positions.
To turn the ball end profile, I initially played around with a HSS profiled tool but it had limitations. Even short material stick-out from the collet was enough to see deflection even by feeding the tool axially vs across the stock. The profile wasn’t exactly spherical & harder to control length. So, opted to first part them finish length plus a couple thou, blued the ends with a felt pen & just shaped the ball end profile using a fine file & magnification. I then inserted them into my Dremel collet as far as it would go in & did finishing with paper. Pics showing various stages of completion. You can get a mirror finish but I doubt it will stay that way for long anyways.
In hindsight, because the Dremel can spin up at much higher RPM than the lathe, it might lend itself to grinding the ball end profile on something a stronger/harder alloy like piano wire or similar shafting stock, which I suspect is stronger than annealed state O1.
-
Next up is timing the planetary cam gears & retaining them into final position. A 15T (module 1) crankshaft gear drives a 15T idler gear which is attached face to face with a 10T gear, these two are the idler cluster that run on an intermediary shaft. The 10T then drives the 40T internal (ring) gear which is connected to the cam plates. The CS to ring gear is 4:1 but the cam plates have 2 sets of intake/exhaust lobes 180-deg apart, which yields the 2:1 crank to cam ratio. The cam plates rotate in opposite direction of the CS.
The plans call for using Loctite to retain basically all of the gear surfaces. I was a bit apprehensive about how to make these joints while getting them into timing position & allowing them to cure because access & visual alignment is a bit hidden. I also had this nagging feeling about glue failure one day. For better or worse I decided on a modified path. Loctite the ring gear into the aluminum cam cup because it has a lot of surface contact area around the perimeter. I decided to drill the CS gear with a cross pin running through the CS so the gear could be removed & replaced one day if required (although matching the pin hole would be an adventure for another day). If I did my math right, the pin should be able to take a decent load but I don’t have a good feel of what loads are involved with driving the cam plates. With these CS gears & ring gear now locked into position, that leaves the relative clock positioning of the 15T & 10T idler gears to be rotated between each other to achieve final cam timing relative to TDC & then locked into that position.
CRANKSHAFT GEAR RETENTION
Before drilling the CS gear, I tried to set myself up for future replacement if the unfortunate requirement ever arose in the future. I positioned the CS between Vee blocks in the mill vise & indicated off both sides of the counterweight flats so it was horizontal, the crankpin pointing up. Then I rotated the 15T gear until I could center align between 2 teeth just using a cone shaped tool extended down from the quill pointing into the gear valley. Then I offset a specific distance along the CS axis from the counterweight surface datum, positioning the pin hole on the reduced diameter segment of the gear. With the gear tacked in this position, the hole was spotted & drilled completely through, slowly pecking & clearing, hopefully to keep it straight. The pin itself is made from a HSS drill. Once the pin is inserted through the gear, a brass sleeve was made to cover the hub so the pin can’t fall out. This shows the assembly in progress. There are also some other spacer shims rings in the driveline to make up various clearance distances between components.
-
more pics
-
Idler Gear Retention. How to properly retain the idler gears together face to face caused me some head scratching, mostly due to small dimensional constraints. The smaller 10T gear which has a PD of 10mm & root diameter of ~8mm & runs on a 5mm idler shaft, so there isn’t a lot annular hub material left for mechanical retention. I followed the plans & turned down about half of the 10T gear to 7.5mm OD which basically inserts into the 15T gear reamed out to that same diameter. This becomes the mating surface to which the Loctite would normally be applied.
-
My calculations suggest Loctite should be as strong or stronger than the small diameter axial ‘pin’ key I could accommodate assuming all went well. I did Loctite tests on blanks of 1018 steel mimicking the gears. Face to face bonding was a fail rather as expected. The joint definitely required the step down reduced hub to resist radial shear? It seemed pretty strong just hand wrenching.
-
I also did some silver soldering tests on two similar sized dummy steel blanks together, more out of morbid curiosity since I have no prior experience with this. I could get what appeared as an acceptable looking joint that seemed to be penetrating the annular gap which needs to be quite small for gear concentricity. But I was getting enough of a fillet that I thought was going to interfere with the teeth meshing & filing it out did not seem like fun. The tester blanks came to a decent red glow by the time the flux turned glassy & silver solder melted. I don’t think the heat would adversely affect the commercial gear alloy as they were unhardened. But it also took some effort to clean the blanks after soldering, so I am going to have to figure out pickling & all that. In summary it was an interesting exercise I would like to return to one day, but I chickened out for this application.
-
Then I tried drilling some ‘pin’ keys centered on the joint line, again using dummy blanks. This actually worked quite well. So, I figured if Loctite was good & pinning was good, maybe I would just go overboard & combine them.
-
Once the cam timing was established relative to TDC, I tacked the gears using CA glue to preserve the position & marked the gear teeth with little ID dots for reference. I set the gear cluster into my prior boring fixture & replicated the pin key drilling operation. I re-checked timing one more time, all appeared good. Now just a matter of assembling the cluster together with Loctite outside the engine.
Including a picture of the 5mm OD axle for idler gears sitting in the front gear plate with its bronze spacer washer & retention screw.
-
Just to revisit the timing on this engine which I reverse engineered using the cam profiles. Inlet opens & exhaust closes equally either side of TDC, which makes it relatively easy to set the cams (I suspect by intent). With piston at TDC, you just rotate the cam plates until the tappet travels are equal to one another during the transition point.
-
Nice looking parts :ThumbsUp:
Thank you very much for taking us along your thoughts, experiments and final solutions :praise2:
Repetability is indeed very important in production and service :ThumbsUp:
Per :cheers:
-
This is maybe a good spot to insert some miscellaneous items. Gasket making. My instinct was that gaskets on specific mating surfaces they would be beneficial. Or at least that’s what I usually see present on commercial engines to seal air/gas, fluids or even help with fastener retention under vibration or heat cycles. The plans were a bit vague on this other than the nose case oil bath area.
I did some experimenting with typical squeeze tube type sealant/gasket products with mixed success. There are so many products out there & admittedly I don’t really understand the variations of metal-to-metal vs in conjunction with gaskets. Actually, of the goopy products I liked, the problem was usually they worked too well. Disassembling the engine parts was quite difficult because of their delicate size & cleaning off stuck residue was a chore. I expect to be in & out of the engine often so I wanted something that lent itself to that. I can produce CAD based export formats for a computerized cutter, I don’t have a machine & it seemed excessive to outsource it for the low parts count plus spares. I see there are some interesting cutting machines used by crafters for cutting stickers & such, but I suspect the software/import capability might be another rabbit hole & again hard for me to justify.
So, I went old school & just hand-made ‘acceptable accuracy’ templates from scrap MDF to act as a cutting guide. I laminated my paper shop drawings onto the MDF & cut them out on the scroll saw. The gasket material I found (actually copied from another builder on the forum) was Teflon sheet, I believe also known as PTFE. The nice thing is it comes in very thin sheet thicknesses, starting at 0.001” depending on the supplier. Its impervious to oil & fuel & even used as head gaskets that see significant heat. I sprayed a light mist coat of adhesive onto the material which tacks it into position on the template. Then cut the outline along the template with a sharp Xacto or scalpel on a cutting mat.
I first tried drilling the gasket clearance holes for, in my case, M3 fasteners to pass through but a drill seems to make a raggedy non-circular profile even with backing board behind. So, I made a simple tool from O1 so that I could harden it & preserve the cutting edge. I used a 4mm ball end mill which made a natural edge to the ~3mm shank. It cut the sheet with a slight twisting motion or using cordless drill. I think the slight give of the cutting mat helps & also preserves the cutting edge. A punch style template might make better holes but would involve another mated template. I also think a thinner, harder cutting template like 1mm aluminum or plastic might allow better access for the blade on internal holes, but the MDF will last for what I need it for. To release the finished gasket from the template, it just needs a spritz of acetone or thinner. The spray adhesive dissolves clean & the PTFE is impervious.
-
Similarly, manifold gaskets.
-
I found a stick of Teflon/PTFE online & used it to make the washer seals for intake & exhaust ports. It mates between the head counterbore & the trumpet profile on the metal tubing, squeezed by the port nut. The material machines quite nice as long as the tools are sharp.
-
With the sub-assemblies now coming together, I revisited my original master rod components & made a few re-do’s. I decided I wanted a slightly better fit between the bronze crankpin bushing bore on the crank pin OD. So rather than ream the bushing which I think was the reason for slightly loose fit, I used a boring tool. The wall thickness is quite thin, maybe that influenced reaming. I also tweaked the front facing flange thickness while I was at it to accurately center the MR to the bores, even though it isn’t really critical. I used Loctite to retain the bushing into MR body & with that done, drilled 3 oil passage holes at slightly offset positions down the crankpin length. The spacing had a domino effect on pin plate thickness & this time I made a bronze washer which will see some occasional rubbing from the retention clip
-
The spacing had a domino effect on pin plate thickness & this time I made a bronze washer which will see some occasional rubbing from the retention clip.
-
Around the same time, I came to notice how close the face of master rod occurred relative to the crankcase recess groove. I thought surely, I must have machined something incorrectly but everything checked out to plans. The MR is centered & nothing should really allow it to drift fore/aft too much, although the MR does have a bit of necessary clearance float between the crankpin bushing & retainer clip. It just made me a bit uncomfortable should a tiny fragment decided to lodge in there, or if I didn’t seat the bearings quite right or… Not that we can predict disasters but I didn’t think crankcase strength would be compromised by opening up the groove a bit. So, I made a holding fixture, dialed in the ID & took off some material either side of the groove, preserving the same depth. Made me feel better.
-
I don’t think I showed pictures of the piston with the OS-56 rings. Here they are. I basically mimicked the groove dimensions to the stock OS piston including the same crown undercut to ease ring installation. As far as I could determine they were a good fit in the liner bores but will be proven later. For interest sake, the section dimensions are quite close to Trimble calculations. Next engine project I will have a go at making my own.
-
When my propeller arrived, it was a different nominal thickness than what the plans presumed which had a knock-on effect to the drive washer & therefore the split cone its mated to. So those parts had to be re-made. I made a slightly bit thicker bolt plate while I was at it & matching drill jig.
-
It going to be a Magnificient Engine when you are finished with it :praise2:
I reallt enjoy reading and watching the pictures :cheers:
Per
-
Nice work :praise2: :praise2:
Your thoughts on the cam drive are interesting :thinking: I like the idea of being able to dismantle the system rather than using Loctite but I am not sure how your pin will cope with the alternating load from the cams.
Is that a special cut down digital caliper that you are using to measure the crankcase?
-
Thanks Roger. That's a good point about alternating vs steady load from cams. I can't recall if this was the exact cross pin drill size I used, but I approached it rather simplistically to size the pin to meet or exceed shear strength of Loctite. I'm sure there are variables on both methods so rather uncharted waters. I was going to rig up some kind of torque measurement because the actual resistance during cam action is quite low. What gave me some degree of comfort is hand turning the assembly with a stub prop, I could easily rotate through the cam action with my index finger at maybe 2" radius. Not very scientific I know. I think its getting some mechanical advantage through the planetary gear drive? Anyways, pray that it works. Next engine I will have a proper key. The challenge is with these small gears, there really isn't a lot of hub material or assembly room to work with, but it is doable.
The caliper is called a hook caliper, Asimeto brand. But OMG the prices of these things have escalated over the years.
https://www.asimeto.com/category-Depth---Height-Gauges-03.html
-
The mechanical parts were basically complete at this point. I decided to make a leak down tester rig to sanity check the cylinders under pressure prior to running. The basic principle is you have two identical pressure gauges with a small diameter orifice restriction between them. Regulated pressure is applied to the input upstream gauge. The downstream gauge output is connected to the cylinder head by a fitting screwed into the glow/spark plug hole. With the piston at TDC & both valves closed mimicking combustion, the gauge pressures should read the same. If the downstream gauge pressure is lower and/or diminishes over time, it indicates a leak in the system. But it can’t distinguish leak between ring seal, ring gap or valves… because it’s a collective system. This is why the tiny orifice restriction between gauges is important, we want to see any pressure change without the supply replenishing just as fast so to speak. I don’t have a feel for how much pressure over how much time is acceptable. More of a Houston, we have a problem thing. My valve/seats were vacuum tested to the extent of negative pressure previously, so I was hoping this would show more ring related results at elevated positive pressure.
The parts were relatively inexpensive Amazon components including the hose & quick connect fittings. I machined an extended length spark plug adapter fitting to match the thread & incorporated an O-ring to seal.
Apparently on full size engine testers the orifice is of defined size. But because our model engine volumes are smaller, the orifice must be reduced. The smaller the hole, the more sensitive are the readings. I’m not sure if it should be reduced proportional to displacement, but I had a few data points from other model testers I came across. My friend used a #80 drill (0.0135"). I asked him how he came up with that & he said it was the smallest drill he had at the time & it works, ha-ha. Also, Don Grimm on the HMEM forum published his tester plans which I subsequently stumbled on & I believe he used 0.026”. I found a tiny restrictor we used on RC pneumatic retract gear systems, but the hose barb diameter is very small ~1/16” so would have required extra machining to integrate. So, I made a restrictor by plugging a standard pneumatic brass coupler fitting with a #80 pre-drilled orifice segment, glued with Loctite. It seemed to work. Then I realized what I thought was a regular on/off pneumatic valve I purchased was actually a pretty fine adjustable needle valve. It already has threaded fittings so I installed it in between gauges to compare. If I just crack the valve, it flows quite slow to the extent the downstream gage takes a while to equalize the upstream gage with the tubing blocked off. So for simplicity & some flow variability, I would recommend going that route if you build your own.
I went ahead & tested the 5 cylinders thinking it should at least be indicative of apples-to-apples comparison among all cylinders. I used about 45 psi initially & then 60 psi when nothing bad happened. The pistons had a light coating of oil normal for assembly. The good news is, no problematic leak off was seen. The gauges equal one another & will sit that way for several minutes at least. I left the crankcase open so I could see the underside of the pistons. Over time a tiny bubble could be seen which I attribute to ring gap & brand-new rings/liners. If I push on a valve, it blows down, re-seats & gauges re-equalize again. I put the same test rig on a known used RC engine & replicated the results (oops took picture with needle valve closed)
It is advisable to somehow mechanically lock the crankshaft at TDC before applying pressure. Otherwise, the engine will faithfully reproduce a combustion stroke with an unexpected & jump on the workbench. Ask me how I know.
-
Glow plug drivers have been discussed a few times on the forums so I’ll just try & summarize a few points as I understand them. A typical plug requires ~1.2-1.3 volts & draw 2-3 amps each depending on variables like the plug element, state of condition, how much fuel wetting, fuel composition variations etc. They can briefly take a bit more power but it shortens life. The wire glow elements come in various gauges & material flavors depending on the purpose. Most are exposed wire viewed from bottom, some plugs have an idle bar or shield.
For RC purposes the plugs are typically only energized for starting, they then sustain glow during running conditions every combustion stroke. 4-strokes engines usually benefit or require a heavier glow element vs. 2-strokes, presumably because of the extra dead time between combustion. FS (Four Stroke) plugs generally draw a bit more power but not much. In some installations glow plugs are switched on during idle for more reliability or for inverted cylinder arrangements which tend to run richer which would be the case for a radial. In that case a remote battery power must be carried by the model & of course weight may be a factor.
The simplest driver is a single NIMH cell (or NICD back in the day) typically integrated to a plug clip. These cells have output voltage quite close to plug requirements. It just needs to be of sufficient C-rating & maH capacity. Some excerpts from OS 5-cyl documentation
-
Next are commercial or shop designed circuit-based drivers which may offer added features like regulated/adjustable voltage, self-compensating current to help if the engine becomes fuel loaded or degrade, responding to element resistance change, I guess. Many are trending to more modern lithium-based batteries especially where weight is a factor. They are quite prevalent, come in many mAH capacities, have much higher current rating & higher energy density. The downside is lithium packs are nominally 3-4 v/cell, so a 1S (single) does not make a good match to 1.2-1.3V plug voltage, hence some kind of circuit is required. There are also commercial, multi-cylinder airborne driver modules with more TX flight control features because they are plugged into the RX. For now, I am just in test stand mode. Weight is no concern, just portability, ease of use etc.
https://www.justengines.co.uk/shop/ignition-systems/on-board-glow/five-cylinder-glow-driver/?v=3e8d115eb4b3
https://www.sonictronics.us/glow-drivers/single-cylinder-drivers/3-9-cylinder-set-up/mcd475-4.8v-pulsed-on-board-glow-driver-five-cylinders/
https://rainbow-tronic.de/en/cartsearch/index.html
The wire harness to each of my O5 radial plugs works out to 6-10” length depending on where they would come together behind the firewall to meet the power supply. I had some inventory 2200 maH sub-C NIMH cells kicking around so as a test I soldered 5 in parallel (one per cylinder). A single cell ignited the dry plug sufficiently & confirmed the voltage/amperage range, so that was a viable option. But as the cells deplete, the glow intensity does diminish. There is also voltage drop along the harness wire & the clip, so a lower resistance multi-strand wire is preferable as is keeping oil off the clip so there is good contact.
I’ve seen various harness clips for RC use. Some are like an e-clip that snap to the stem groove. Some are like a push & rotate engagement that lock on the hex body. My plugs are recessed relatively deep in the head so I needed something physically longer to reach. I found some low- profile ‘remote’ RC harness / plug clips on AliExpress & ordered some to evaluate. The clip body is basically a brass cylinder with a spring captured inside which snugly grips the plug stem making electrical contact. Note that 2 sizes are offered, one for thinner (2S) and one for thicker (4S) plug stem diameters. The system looked as good or better than I could make & seemed like it would hold under vibration. One could also bend or re-solder the wire more at a right angle & re heat shrink, making it look like a faux boot.
-
While poking around AliExpress I also came across some on-board RC igniter modules. They are purpose designed to output the correct plug voltage. They also allow a wide range of input voltage which was desirable because I have spare LiPo cells & charging equipment. I bought one to try & it seemed to function as advertised with a bit stronger glow than on my NIMH pack. I’m not sure if the modules have features beyond voltage regulation since I am electrically challenged. I decided for the net cost to sandwich 5 together operating in parallel, one for each cylinder to common battery source. I also wanted to switch them on/off independently both to start & also to evaluate how idle/transition behaved on dedicated upright/inverted cylinders out of curiosity. I snipped off the pretty anodized & chromed clips for some other project.
-
I found a plastic project box to house the modules & switches & commenced my Neanderthal electrical construction. I needed something like a bus bar to tie the leads in common, but I didn’t see the point in a bunch of screw terminals & the wires were pretty small gauge. So, I cut some copper from scrap 1/16” sheet & just soldered the wires directly. The modules were sandwiched together with heat shrink & everything sits on a G10 plate with standoffs. With the switches it’s a bit of rat’s nest but hopefully functional.
-
more pics
-
I made a test stand from 3/8” birch plywood. The joints were glued & screwed together for rigidity & a couple coats of 2K clear so it can be wiped down. My flying field has a very beefy wood table that was used for engine runups back in the day, so for now I will just screw the base down with deck screws which will save me making a dedicated sawhorse or buying a portable work table. The exhaust pipes will blow outboard of the firewall, thus providing copious lubrication to the operator, but I can rotate them within the head port so at least they don’t blast directly at the firewall face as they are quite close right now. One day I would like to make an exhaust collector ring, but that’s a project for another day.
The engine is mounted on 5 aluminum standoffs which have M4 clearance holes, so basically bolt passing through the standoff into the threaded manifold mount plate part. The vertical ears give the firewall rigidity to the base & somewhat house the glow driver box. I routed the plug harness through a single hole to avoid the carb opening & then to individual cylinders. A LiPo battery is hooked up to the input power.
-
The fuel tank is just a regular RC style held in a cradle, but I can locate it up or down if that affects running. Generally, tank center should be about in-line with carb & it should pull full to empty without going lean. If its positioned high it can provide a bit of head but also risks fuel free flowing into carb & flooding. I made a makeshift throttle arm with a pinch clamp. I’m not sure what carb type will end up on the engine, so keeping things simple for now.
-
Not much room to operate the Needle - but other than that - I love the whole setup :ThumbsUp:
Plus it is a nice display stand too :cheers:
Per
-
Yes the OS carb came from a more modern 2-stroke principally based on desired orifice size. And well, they make nice carbs. OS now angles the needle valve adjuster axis back away from propeller proximity in order to better maintain finger tips to their stock length. But mounted in my orientation it faces forward no getting around it. Its only slightly awkward but I can reach it. I think its a result of originally anticipating 1/4" thick firewall but changed to 3/8" on the fly. I can easily modify the carb adapter fitting.
-
Apologies for my posting lapse again. Well, the day finally arrived with the realization that I somehow had come to the bottom of my seemingly endless To-Do list. There was nothing left to make. After <ahem> ‘a number of years’ it’s a rather weird feeling.
My preference was to attempt a run up in the back yard, fully expecting a multitude of unforeseen teething pains, requiring access to tools etc. But I don’t think my neighbors would appreciate the unmuffled noise (assuming there would be any noise). I decided to take the engine to my local flying club where we still have a heavy, oil-soaked run-up table from yesteryear. It doesn’t see much action these days, but it was a simple matter of screwing my test stand to it. I mentally prepared myself that this was probably going to be the first of many road trips over the summer to get it going.
I have collected a few different carbs & have machined adapter plates so they could be swapped to the back of the manifold. But once the engine was mounted to the firewall pillars & the ignition wires were routed & throttle control hooked up, swapping out carbs was not going to be as quick as I anticipated. So, I decided to go with the O.S. carb first. It has the smaller orifice size & what I consider nice mixture control features, so hopefully that would assist early running attempts which was the prime objective for now.
I felt that hand starting (propeller flipping) a new, shop made, relatively unknown engine was probably wishful thinking on my part. I blew the cobwebs off my old RC Sullivan starter, which has not seen an engine for a dozen years, but discovered the NiMH cells were in bad shape. I could not trickle charge them back to life & had no spares. I could have retrofitted a Lipo or wired it to my 12V deep cycle battery, but I figured probably just as well because the silicone spinner cone was not a good profile match to my smallish prop nut. But mostly I was apprehensive about its relatively high torque & RPM. Should the lower cylinders become flooded, or any internal parts became loose, a strong starter would probably inflict more damage. So, I made a makeshift drive dog accessory to use in my 18v cordless drill. Basically, a hub with short pegs to engage either side of the prop near the root & a center hole to allow the prop nut to protrude into. It wasn’t pretty but I thought good enough for now. The drill is a typical planetary reduction drive so lower RPM. It also has a variable clutch setting so I could utilize that as a bit of safety release. More on this later.
I turned it over by hand choking the carb until I could see fuel flow in the line. I put a few drops of fuel directly into the top cylinder glow plug hole, set the throttle to 1/3, turned all the ignition plugs on & commenced turning it over with the drill. Imagine my astonishment when it barked to life! I think I just stared at it for a while not quite believing what was happening. It sounded a bit rough & choppy but all 5 cylinders were firing. I lowered the throttle a bit to where it ran OK but not wanting to quit. The needle valve seemed insensitive but I could see the exhaust was oil wet & I was happy to let it run rich that way for a while. After about a minute I shut it down. Nothing seemed hot. No parts were sticking out of the side of the crankcase. I decided to grab my iPhone & record the happy occasion.
Now I must confess, this monumental day occurred earlier this summer. I thought I would subsequently figure out how to get a YouTube channel to post a video link, but time commitments got the better of me. So you will have to accept these video stills for now & use your imagination of the sound. I pledge that I didn't Photoshop a blurred prop in motion haha. I have subsequently had the engine apart for inspection & modifications a few times, so will document a bit of that now. It is running better each session. I was just about to give it another go these past weeks but the winter white stuff appeared, so I will have to wait for a better day.
-
Excellent :praise2: :wine1:
I'm looking foreword to seeing/hearing the video :)
-
First a BIG Congratulations - you have a runner :whoohoo: - that must have felt very special :praise2:
Would love to have seeing/heard the Video - but it can wait until you're ready ....
Per :cheers:
-
Outstanding! Getting a start on the first try - also outstanding! Congratulations!!
The finished engine looks great as well. A very nice job all around. :ThumbsUp: :ThumbsUp: :cheers:
-
Incredible work! Sounds great in my head, hoping to hear it for real soon! :ThumbsUp: :ThumbsUp:
-
Congratulations! That's so exciting to see your engine run for the first time! :pinkelephant:
Kim
-
This might be in bad taste on maybe contravening forum rules, but I was able to utilize a video direct upload feature on the other forum (post #298). It may take me a while to sort out becoming a YouTuber or exploring other video hosting options. It took me long enough to figure out how to edit the rudimentary clip, but I'm slowly dragging myself into the modern era.
https://www.homemodelenginemachinist.com/threads/ohrndorf-5-cylinder-radial.32844/page-15
-
I took a look using that link, and even after wading through screenfuls of horrible ads, I couldn't see your running video there.
-
I did find the video eventually - way down, close(ish) to the bottom of the page. Lots of adds though :(
It was a great run! I can see why you are pleased, you should be! ;D :ThumbsUp:
Kim
-
I did find the video eventually - way down, close(ish) to the bottom of the page. Lots of adds though :(
It was a great run! I can see why you are pleased, you should be! ;D :ThumbsUp:
Kim
Were you logged in there? I was not, found the post where it said heres a video but it didn't show. Great reminder of why I stopped posting there, horrible load of ads.
-
I imported the video into my own youtube account, and post it here. I hope you don't mind, petertha! I did not make it public, only "unlisted", so only those with the link can view it.
https://www.youtube.com/watch?v=Imz5YBPUymQ
-
Thats awesome!!
-
Great achievement............ :cheers: Terry
-
I did find the video eventually - way down, close(ish) to the bottom of the page. Lots of adds though :(
It was a great run! I can see why you are pleased, you should be! ;D :ThumbsUp:
Kim
Were you logged in there? I was not, found the post where it said heres a video but it didn't show. Great reminder of why I stopped posting there, horrible load of ads.
Humm... not that I know of. I may have been a member of the site many years ago, but I haven't logged in for years. And it was offering to let me logon through Google. I opted not to. So I don't think I was logged in...
Regardless, Ron posted it here, so that solves the problem.
Kim
-
Congratulations petertha !! I can well imagine how pleased you must be.
I have thoroughly enjoyed following your progress via this thread. Thank you for posting in such detail throughout.
Regards
John
-
Sounds and Runs Great + with some Urgency when you open the Trottle :praise2:
Per :cheers:
-
I imported the video into my own youtube account, and post it here. I hope you don't mind, petertha! I did not make it public, only "unlisted", so only those with the link can view it.
Thank you Ron!
-
I think I did about 5 runs of a couple minutes duration each. I didn’t want to push my luck any further the first outing. Mostly what you will now see is lots of oily pictures from initial teardown. The components looked acceptable, but I also discovered some near miss problems which I’ll discuss in more detail. The good news is there appeared to be a decent oil slick on all the internal parts. Oil residue was migrating sufficiently forward in the engine to lubricate the cam plates, gear train, front bearings & rod assembly either by blowby or induction charge. I did see quite a bit of cast iron ‘dust’ entrained in the oil which would be quite abnormal for a commercial engine break-in. It doesn’t look very nice but I couldn’t feel anything one could describe as grit by just rubbing the oil residue between my fingers, more like a dark watercolor like stain. For now, I chocked this up to bedding in new rings within shop made cast iron liners. Of note, this blackness diminished more & more with every subsequent run but I stopped taking pictures.
The cam plates showed shiny skid tracks from the lifters wearing through the black heat treat coloration, more like polishing but no grooves. I could also detect some unequal contact wear thickness near the rise & fall cam fillets, but too early to comment on that.
-
On my last runs I noticed a few cylinder flange screws loosened again after I had already tightened them the prior run. This may have been contributing to what my ear said was rougher running. One of my pushrod tubes was starting to jiggle around, probably as a result. Another good reason to stop while ahead. A floating cylinder is a bad thing. Thankfully the M3 threads were still in good shape but this issue required attention. Some other parts pics.
-
Crankshaft & rods
-
The #1 piston assembly looked pretty good overall. Lots of lubrication, no shiny wear areas or hot spots. The ring looked like it was just starting to wear in evenly enough around the periphery. A few vertical scratches on the piston here & there but nothing of consequence. However, I noticed a little divot on the piston top which I assumed maybe from particle ingestion or something, but on closer inspection looked remarkably like a crescent shape valve impression. It was on the exhaust side only. I immediately checked around the edge of the edge of the exhaust valve but could not see any deformation of feel a burr. As I proceeded to each cylinder I saw more or less the exact same impression on all piston crowns. Not good. I immediately suspected my cam timing was perhaps incorrectly set a gear tooth off, but my witness marks were correct… unless I somehow messed up the clocking from the initial get go. I also noticed considerably more valve gap on the exhaust rockers than was pre-set. I’ll return to this issue under remediation, but I think I used up one cat life. This could have been much worse.
-
Remediation pics. First the easier stuff. Here is my initial makeshift drill starter. It mostly turned the engine over OK to where it would fire, but the prop engagement pegs were mangling the delicate trailing edge root despite my attempts to rubberize it with tubing, heat shrink & electrical tape to help snub the contact. I was concerned about weakening the prop to the point of it breaking.
My spinner nut fell off a few times which caused a few Keystone Kops episodes of locating parts in the grass, so I made a more robust wrench to tighten.
-
After subsequent runs it was becoming obvious the drill starter had to go. It continued to chew the prop and had more difficulty turning it over as compression improved. I also suspect that as the engine began firing, the drill’s gear drive was probably limiting it from free running until I could withdraw the peg drive, which is probably not healthy vs. a one-way clutch mechanism or freewheeling motor with power off. I searched for gear reduction drive RC starters & realized the RC world has changed. There are some big boy starters for much larger, typically 2-stroke engines. I was aware of Kavan planetary gear starters used on RC 4-strokes back in the day, but they are no longer made. Eventually I found this PGD reduction starter from Just Engines in UK. I bought a dedicated 4S (14.4v) LIPO hard shell RC battery pack & made a plywood carrier frame. So far it has worked very well. Fortunately, the silicone cone could be flipped to expose a smaller diameter hole, so I made a matching, lager spinner nut.
-
I actually made a tester Teflon gasket for under the cylinder flange earlier but elected to omit them initially. I wasn’t too keen about using Loctite on the threads if it could be avoided. I sourced some 0.002” thick sheet so it wouldn’t affect CR very much. As it turns out, the gaskets did some good. The screws thereafter stayed intact on subsequent runs, so maybe it provided a bit of conformance to the prior metal on metal contact?
-
The exhaust valve indentation on the piston tops was a serious issue to address. My first suspicion was that I had incorrectly placed the ring gear cam plate assembly onto the idler gear cluster off by a tooth. This would have the timing effect of lagging the exhaust valve closing beyond TDC (black bars on the timing diagram). This might explain why there was no matching intake valve indentation on the intake side of the piston. All pistons had the same exhaust only mark dent. One would think altered timing would mean rougher running, but I really had no smooth/rough reference experience yet. It seemed to idle & transition reasonably well but this was my first rodeo. I didn’t take it beyond half throttle for more than an occasional blip. But it turns out, I my cam position was indeed correct, my original witness alignment marks were correct.
This engine is relatively simple to set up & verify in this regard. Exhaust valve closure & intake valve opening occurs equally either side of TDC.
-
So, I commenced measuring all the contributing dimensions (there are many). Rod throw, piston height, cylinder deck height, cam lobe rise, valve clearance… Everything was within a thou of drawings. I did deviate slightly from drawings by decreasing the valve seat width, but net effect actually increased the valve cage submergence up into the head chamber & served to provide even more valve clearance.
I did a little bit of CAD motion study & concluded there was indeed theoretical clearance but it was actually quite close which I never bothered to consider before. If I was seeing the effects of valve float or temperature increase, this might add up to several thou & that seemed to be the extent of valve strike impression.
I’m really not sure but in any event, it needed to be dealt with, so I considered my options. I could add a head shim & gain some valve clearance that way, but at the expense of compression ratio. I estimated I was nominally at or under 9:1 but CR drops to 8.6:1 with only 0.005” shim or 8.3:1 with 0.010” etc. Maybe I had sufficient CR to spare but it seemed counterproductive to chase that option if the interference represented the same 0.010” confined to a tiny, localized impression area.
I could add a shim under the cylinder flange which raises the head from the fixed piston throw. That has the same CR reduction effect, but I was already contemplating some kind of gasket under the cylinder flanges to help with metal-on-metal mating & bolts loosening.
The other option was to cut extended crescent shaped recess pockets into the piston tops aligned to the valve strike area. I couldn’t go too crazy on this depth wise, limited by the piston crown thickness, but on paper it bought me significantly more potential clearance with minimal CR change. I could always still do the shimming if required.
I still had my piston holding fixture used for milling the rod clearance pockets. The fixture has a through hole for the wristpin, so that would self-align the piston orientation. Then it was a relatively simple matter of angling the piston/fixture in the mill vise to the valve angle & dropping down an endmill to increase the pocket dimensions. I did the other (intake) side the same just as a precaution & smoothened the edges with rubber abrasive. You can see the before & after net result.
-
Hello Peter
You could try opening the exhaust valve tappet gap and ride higher up the exhaust cam lobe.
Mike
-
I made sets of brass head shims from various stock thicknesses between just in case.
-
Hello Peter. You could try opening the exhaust valve tappet gap and ride higher up the exhaust cam lobe.
Mike
Good point Mike, I neglected to mention that option too. That essentially shortens the timing duration bars visually on my little chart & ideally misses the TDC. I reviewed the recommended O5 rocker/valve gap & then went on a bit of mission checking other engines. O.S. has had the same dimensions since the dawn of time & were actually a bit under mine. If I recall, the Jung engines have a wider gap on exhaust only, maybe suggesting elevated temperature effect? I'm kind of skipping around my timeline, but the subsequent runs with modified piston valve relief crescents fixed the issue completely. No more contact. So the head shims never went in but the 0.002" Teflon gasket under the cylinder flange did.
Also, I made my valve stems flat topped with just a tiny chamfer, another thing I didn't really think much about. The rocker pads are of course curved but it seemed to me at full deflection it could have been pushing on the crest of teh valve stem. I'm pretty sure one of the commercial 4S engines I had apart had domed valve stem tops, maybe this factors into things? Splitting hairs here but I will pay more attention to this stuff on subsequent engines.
-
A few more pictures to get caught up to present day. On subsequent running sessions, the engine continued to smoothen out & could also reliably hand start if still warm. The cylinder flange bolts remained tight & no more valve/piston competition for the same real estate.
But I had another unexpected incident that could have been much worse. Another cat life consumed. After a number of runs the engine basically quit from medium throttle. As I turned it over by hand, something was obviously very wrong. It was very stiff through the rotation. No grinding or clunking noises but lots of resistance. On the drive home I thought a seized bearing might explain this. Under teardown, everything looked heavily lubricated & much clearer, much less black soot. All the bearings seemed fine. With the ring gear cam plate assembly off I could spin the crankshaft freely.
But what became obvious is the idler gear assembly was seized on its shaft which extends off the gear plate. I’ve included an earlier build pic to show the stock configuration. On the front of the shaft is a teeny bronze washer, spot drilled to accommodate a M2 flathead screw. I could still get a feeler gage between the washer & front gear indicating the running gap was still there & the bolt was still secured with Loctite. But it took some persuasion to get the gear cluster off revealing a scored & heated shaft. That then had to be removed from the aluminum gear plate with heat & persuasion.
-
I never really cared for this washer/screw arrangement but assumed it was necessary for disassembly, but it actually isn’t. The crankshaft can just exit from the rear with its gear still on the shaft & disengage from the idler gears axially. My temporary conclusion was that the steel gear running on (hardened/tempered O1) steel shaft was not getting sufficient lubrication axially through the shaft/bore annulus.
So, I decided to sleeve the gear cluster bore with bronze as a better material & also drill some teeny radial bleed holes through the roots of the gears to lubricate the shaft for good measure. It was a bit of crap shoot that oil would want to migrate inward to the shaft when the gear rotation would want to sling it out, but I was hoping an oily coated gear might squeeze some oil into the holes, kind of like a rudimentary oil pump mode.
The next challenge was cleaning up the badly gouged gear bore, but I had precious little material left before I encountered the axial key pin, which was in fact a HSS drill bit slug. For reference the small gear is 10-tooth & large gear is 12-tooth M1 running on 5mm shaft. I utilized my gear fixture & stopped boring when I got to the pin, turned some bronze & set it in with Loctite.
-
I made a new shaft with an integral end flange to retain the gear cluster that way. The advantages are it eliminates the bolt & washer business which could come loose one day & runs dangerously close to the back of the ring gear plate as is. The disadvantage is that the shaft is somewhat permanently bonded into the gear plate with Loctite. A tradeoff I accepted assuming I could again use local torch heat to remove it, even though it put up a fight coming out. My plate was undamaged but I think if it comes to that I’d make a new plate out of steel with a meatier shaft, although it can’t get too large a diameter ~6mm? just based on the inner diameter of the 10T gear.
I didn’t take a good picture but I drilled two ~1mm oil holes into the 10T gear & 4 holes in the 12T gear. I also drilled two axial oil bleed holes through the gear plate on either side of the idler shaft, hoping to get lubrication from the crankcase chamber into what becomes the back face of the 12T gear. Both ends of the gear have a washer made from brass shim stock. I am happy to say this seems to have worked. Yet another run & teardown showed the shaft was nice & oily with the idler spinning freely. Lesson learned.
-
Looks good and I really hope that you have solved the Lubrication issues with this :ThumbsUp:
Per :cheers:
-
The first run sounds good :praise2: :wine1:
I like the way you are very methodically working through the various teething problems :ThumbsUp: :ThumbsUp:
-
For some reason I have been quite erratic in reading & following this thread, and for some reason thought I was completely up to date, but today found I still had quite some pages to catch up on, so have just read to the current end.
I have to say this build has impressed me. The attention to detail in both the machining and also the thought processes and reasonings why along the way, the fixtures devised and set up displayed, have all been so enjoyable to read and see in the photos, and so informative, and the end result of a beautiful engine a joy to to behold. Loved the video too, lovely sound running.
I have learned quite a lot and have bookmarked this thread as a reference, to help me in the building of the radial I am engaged in. I will be reading through this thread again, for sure.
Thank you Peter.
Chris. :cheers: :ThumbsUp: :ThumbsUp:
-
Thank you for the nice compliments, Chris. In all fairness my posts were pretty spotty over an extended timeframe so it would be fair to surmise at many points 'he gave up', 'no, looks like he's back again' haha.
I suspect more reasonable people would have started with a single cylinder & then progressed with a multi cylinder, but it is what it is. Eventually I got over the goal line. I'm thankful of this forum & all the talented people posting their builds & sharing of knowledge. I look forward to your build!
-
What Laurentic said goes for me too. Glad to see this one run, if maybe not perfectly yet. The video clip sounds wonderful, you should be quite chuffed with progress to date. :cheers: :popcorn: