Model Engine Maker

Engines => Your Own Design => Topic started by: doubletop on June 27, 2019, 11:10:53 AM

Title: 30cc Flat Four (Puma)
Post by: doubletop on June 27, 2019, 11:10:53 AM

I built the Malcom Stride Bobcat something like six years ago

(https://i.imgur.com/DcfWZ9h.jpg)

(https://i.imgur.com/X2pmPaX.jpg)

(https://i.imgur.com/777gVgT.jpg)

When I was building it t occurred to me that the crank could easily accommodate another pair of cylinders in a flat four configuration.
 
(https://i.imgur.com/G0P1NbM.jpg)

It was put on the ďto doĒ list. I did build the Lynx and then locomotives got in the way.
 
Jason and Brian beat me to doing a flat configuration but they both did a twin based on Malcolmís Bobcat or Jaguar parts.

Jasonís Ocelot

(http://img.photobucket.com/albums/v156/jasonballamy/Engineering/Nemett%20Ocelot%20NE15OT/DSC02498_zpsiklqtf8q.jpg)

Brianís Opposed Twin

(https://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow029/SUPERMAGNETS%20001_zpsbh9ocofs.jpg)

A year or so ago I needed to teach myself CAD and used Malcolmís drawings as the basis for my learning. That didnít get much further than the parts for the original Bobcat design and a bit of a lash up in the assembly package.

Fast forward to a few weeks ago an I picked it up again and did the drawings for the parts to make the flat four.

(https://i.imgur.com/jydDBYT.jpg)

(https://i.imgur.com/A09Ubpr.jpg)

All Malcolmís engines have drawing numbers -
 
Lynx - NE15S Ė Nemet 15cc single
Bobat Ė NE15IT - Nemet 15cc Twin
Jaguar - NE7.5S   - Nemet 7.5cc Single

Jason has followed the convention with

Ocelot - NE15FT Nemet 15cc Flat Twin

Its been a while but here we go and unless there is a reason or not using the name ĎPumaí this is going to be
 
Puma - NE30FF Nemet 30cc Flat Four

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on June 27, 2019, 11:14:16 AM
 8) I'll be following along

Jo
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on June 27, 2019, 11:38:31 AM
Ö.. and its not vapourware, Iíve made a start

(https://i.imgur.com/H4gnUs6.jpg)

(https://i.imgur.com/gzQSKHo.jpg)

(https://i.imgur.com/GgBWArV.jpg)

(https://i.imgur.com/KPcJqsR.jpg)

Iím not promising rapid progress and there may be a few stumbles on the way. Iíve had to make drawing changes already. But I guess thatís to be expected.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on June 27, 2019, 12:29:00 PM
You have made good progress since we exchanged e-mails the other week, Puma sounds good to me.

looking forward to see the belt driven twin cams turn out rather than the gear drive option, almost seems a shame to cover it up.
Title: Re: 30cc Flat Four (Puma)
Post by: b.lindsey on June 27, 2019, 02:57:08 PM
Looks like a fine project Pete. Watching along here as well.

Bill
Title: Re: 30cc Flat Four (Puma)
Post by: Ye-Ole Steam Dude on June 27, 2019, 03:03:04 PM
Hello Pete,

I will be following along on this build, looks like a great start already.

Have a great day,
Thomas
Title: Re: 30cc Flat Four (Puma)
Post by: Laurentic on June 27, 2019, 06:21:25 PM
Looks an interesting engine already Pete, nice looking start, I'll be following this one along too.

Chris
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on June 27, 2019, 09:43:36 PM
Thanks for your good wishes everybody.

I had to make a start before I posted anything. It would have been too easy to fiddle about in the CAD package tweaking this and that and then getting distracted by something else. Cutting metal makes a commitment to carry on. 

My emails with Jason the other week were around any problems he had experienced with his flat twin and whether I should continue with the flat four or consider doing it as a V4. I was concerned about oil in the cylinders, I have some thoughts and Jason has some suggestions so we'll get to that at some point.

Jason has asked about covering up the belt drive, I have considered that. The parts have arrived from Belting Direct and although I have allowed for the extra size adding a belt tensioner may be a problem. We'll cross that bridge when we get to it. Making a round bearing holder would certainly be easier and help with the setting up. I may well do that for now.

I don't like doing repetative work so making four or eight of everyting will be a challenge so posts here will be infrequent, I'll just show differences to Malcolms original design and sub assemblies as they are made. It won't be a blow by blow 'how to' guide. Malcolms original aricles did a better job than me on that and 90% of the parts are to his original design.

I'm waiting for the bearings to arrive so I'm on the cams at the moment. They need a bit of concentration.

regards

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on June 27, 2019, 10:18:48 PM
Doubletop--Very nice cad work. I wish you great success with the build and will follow along. I anticipated trouble with an oil base, just as Jason experienced with his twin. The revolving crankshaft picks up the oil and throws it into the cylinder on one side of the engine. I solved that issue by having a removeable cover-plate which let me give the crankshaft and rods a good squirt of oil from a can before I ran the engine.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on June 27, 2019, 11:23:36 PM
Brian

I'm planning a deeper sump so the oil has somewere to return to and I have discussed baffles with Jason. Simple plates with slots in for the conrods. They could well be integral with the sump.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Art K on June 27, 2019, 11:46:36 PM
Pete,
This looks like a great project and I will be following along. I totally understand taking your time, we will be here.
Art
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on June 28, 2019, 11:44:10 AM
A chilly Friday night here in NZ so I tinkered with the CAD

Feasibility of adding the oil baffles and an alternative simpler exhaust pipe on the right hand side

(https://i.imgur.com/NPZ6VVY.jpg)

And timing belts

(https://i.imgur.com/Sci8f8z.jpg)

More by luck than design, apparently the pulleys and standard belts I ordered will fit without the need for a tensioner. We'll see.

Magnet disks for the ignition should be easy to install and as Jason suggested the cover can be dispensed with.

Getting a bit ahead of myself though.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on June 28, 2019, 12:26:31 PM
Exposed belts look good, a bit of tarting up of the plain pulleys may add a bit wow factor.

For the sump I was thinking of a trough, similar to what Graham has on these two engines and Jo's Seal & Seal major will have the same sort of arrangement. Once the oil in the trough has been flung out as the engine is started it can only flow back slowly through a small hole or two which limits what gets thrown about. Alternative with your deeper sump would be to have some oil flingers and keep the oil level below that of the crank and big ends so only a small amount of oil gets picked up.

http://www.modelenginemaker.com/index.php/topic,4680.0.html
Title: Re: 30cc Flat Four (Puma)
Post by: cnr6400 on June 28, 2019, 03:34:21 PM
Great looking engine CAD work!  :ThumbsUp: :ThumbsUp: :ThumbsUp:

One suggestion - Looks to me like the crankshaft pulley has about 90 degrees of "wrap" of the belt. I would suggest adding an idler pulley in the non-tension side span between crank and cam to get closer to 120-180 degrees of "wrap". This will reduce stress in the belt and lower the chance of skipped teeth as the belt warms up at high rpm. Just food for thought, I've designed some timing belt systems for a few companies, and had the hoo-ha's with low wrap / high load situations.
Title: Re: 30cc Flat Four (Puma)
Post by: Allen Smithee on June 28, 2019, 08:07:02 PM
Slightly surprised you went for two camshafts - surely with a two-throw crank (so the left and right cylinders are alternate-firing) you only need one camshaft?

AS
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on June 28, 2019, 11:31:31 PM
Thanks for the feedback, thatís why we are here.

Jason - Now I understand what you meant by the curved baffle; I was planning to ask you. I've been away from here for too long and have missed following what others have been up to. It certainly looks like the solution. As well as limiting the amount of oil thrown into the bores it will direct it at the cams. In fact, when I was boring the crank case I had considered leaving the curves in place at the sides and leaving the camshafts in their own separate bore. There would have then been a lubrication problem to solve for the camshafts. I thought that was a step to far at this point and went with Malcolm's approach of a fully opened out crankcase.

cnt6400 - Thanks for the advice. The belt I'm using is a standard 145mm I had expected a bit of slack that needed tensioning but the CAD package tells me not. If I went to the next size of 165mm I could add a tensioner. We'll see when I've got the crank and camshafts in. I've yet to make them and can't dummy them up as the bearings haven't arrived yet.

Allen - Yes; that was my first thought and started out on that route. With a single centralised camshaft the tappet guides would have been quite long, but not really a problem. However, I think the crank would have fouled the camshaft. I could have moved it up a bit and had the pushrods at a slight angle. Not wanting to make too many changes went for twin cam to keep it as close as I could to using Malcolmís original components.  Given a cylinder configuration of 1. front left, 2. rear left, 3 rear right 4 front right.  A single camshaft would give a firing order 1,4,2,3 with 2 camshafts you have the opportunity to do 1,3,4,2 which may be a bit more balanced. Whatsmore a 30cc Flat Four Twin Cam is a bit more sexy.

Pete

Title: Re: 30cc Flat Four (Puma)
Post by: Art K on June 29, 2019, 02:14:48 AM
Pete,
The only thing that I would throw in the mix, not to muddy the water though. Is that most full sized flat fours have a crank much like a inline 4 the end throws up and the center two down. I did see another flat 4 build that had the same crank configuration as you're planning so I know that it works.
Art
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on June 29, 2019, 07:22:09 AM
. Whats more a 30cc Flat Four Twin Cam is a bit more sexy.

I think that sums it up well, when designing an engine that won't really be put to work so weight, performance, etc are not such an issue the designer can just go with what they fancy. If I remember rightly I had to move my single cam slightly further away from the crank and had to alter the gear teeth to suit.

The Jung's flat 4 model has a similar crankshaft arrangement so you should be OK. Malcom did do several articles about crank designs and balance as a build up to the Bobcat series and goes into detail why he opted for a flat crank.
Title: Re: 30cc Flat Four (Puma)
Post by: bruedney on June 29, 2019, 08:00:09 AM
Following along Pete.

Look forward to seeing it in the flesh sometime.

Where are you getting your bearings from? I source bearings from NZ Miniature Bearings if I am not wanting to wait for them to come from Aliexpress sellers

Cheers
Bruce
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on June 30, 2019, 10:48:01 AM
I'm happy that the crank, as proposed, will be OK it will allow a cylinder to fire every half rev so that would balance everything out without needing any balance weights. Again, we'll see.

Bruce - the bearings are coming from Bearings Direct in the UK. Unfortunately, NZ suppliers seem to be overly expensive and although Aliexpress are cheap their delivery timing can be a bit hit and miss.  I may be taking it to the club night on Wednesday.

This weekend has been a bit of a mission in making the cams. After a failed attempt I ended up with two good blanks. Then I struggled to get the rotary table line up accurately on the mill. Leaving it until the next day I had it done in 30 mins. I then made a start on machining the cam profiles but realised, after about 30 steps, I was going the wrong way! That required another blank making.

Malcolmís cam table only shows the 120steps between 300->0>60 degrees. The base circle is another 240 steps so with two blanks 720 steps plus the wasted so about 750. (No need for suggestions of CNC thanks, I get it. This isnít the first job Iíve done that Iíve been winding handles for hours mentally adding CNC to the to do list.)

Malcolm suggests cutting the profiles using the Z axis of the mill. I did that the first time round but as you are cranking the weight of whole mill head up and down, at times only 0.01mm, I found it less than satisfactory. This time I used the Y axis and had far better control. However, it does require the rotary table and fixed centre to be set up accurately along the X axis. If you use the Z axis you just need to ensure the height of the centre is accurately set. Alignment along the X axis isnít that important. Maybe thatís why Malcolm suggested doing it his way?


(https://i.imgur.com/oMUCPjM.jpg)


(https://i.imgur.com/RhMHHay.jpg)

So Iíve now got 8 cams ready to be separated the bosses trimmed to length and the holes drilled and reamed, then thatís another of bigger jobs done.

Pete


Title: Re: 30cc Flat Four (Puma)
Post by: MJM460 on June 30, 2019, 12:34:46 PM
Hi double top, a great thread, I am enjoying following along. 

Donít worry too much about rotating the wrong way when you were making that cam.  In my working life, I was in an office of a very large company who were making steam turbines.  In the foyer was an example of their work, a turbine rotor, about five meters long, with the smaller parts of the shaft over 300 mm dia, and the blades ranging from around four cm long, not very long as it was obviously a very high pressure turbine rotor, as an example of the work they do.  All machined in one piece from a single forging.

I asked how it came to be available to put on display.  Apparently it was machined to rotate in the wrong direction!  It happens to the very best of us.  You can put yours on display beside the engine at a show.

MJM460

Title: Re: 30cc Flat Four (Puma)
Post by: Allen Smithee on June 30, 2019, 08:31:52 PM
Great stuff - really appreciate you sharing. Can I ask a question (I want to understand so I can copy ideas for my own projects!)?

Do I understand correctly that these blanks will each be cut up into four individual cams, each of which will then be bored and mounted on a shaft? If so how will they be fixed to the shaft - press fit, bonding, pinning, silver soldering or something else?

And would each resulting camshaft than be carried in two ballraces, one at each end?

Thanks,

AS
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on June 30, 2019, 09:00:00 PM
Allen--They are attached to the shaft with Loctite. It holds fine, and an added benefit is that if you install the cam segments ass backwards as I did, a little heat from a torch frees them up very easily and lets you turn them around.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: bruedney on June 30, 2019, 09:35:45 PM
Bruce - the bearings are coming from Bearings Direct in the UK. Unfortunately, NZ suppliers seem to be overly expensive and although Aliexpress are cheap their delivery timing can be a bit hit and miss.  I may be taking it to the club night on Wednesday.

Hi Pete
I find NZ Miniature Bearing very reasonable https://nzminiaturebearings.com (https://nzminiaturebearings.com) depends on size and what quality you want. I have also found and Aliexpress supplier that is quite consistant in their shipping https://fushi.aliexpress.com/store/511615?spm=a2g0s.9042311.0.0.27424c4dZsZPaM (https://fushi.aliexpress.com/store/511615?spm=a2g0s.9042311.0.0.27424c4dZsZPaM)
I hope to be there on Wednesday but depends on how things go today and the next couple of days. Lee's mum passed away last week and the funeral is today.

Regards
Bruce
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on June 30, 2019, 10:01:09 PM
Bruce - Sorry to hear about Lee's mum, hopefully I'll see you on Wednesday. On the bearings I'll admit to a bit of laziness. The bearing specs in the ME article for the Bobcat have an error so I went back to Bearings Direct to check what I had ordered last time. As I was there it was too easy to just re-order.

MJM460 - In my case if I had been on the turbine rotor job the 4cm blades would have been 2cm. I moved the Y axis in rather than out from the initial cut for the base circle. I was going well and went in for lunch and when I came back to the job I realised what I had done.

Alan - Yes ball races each end you can see them in the CAD pictures. Brian has answered you on the fixing of the cams. As he says the benefit being if you stuff it up you can go again. Given I'm doing two shafts with different firing order there's plenty of opportunity to do that. Fixing the cams to the shaft will be some time off yet and be done when I confirm the firing order and ignition so the whole thought process is done in one session. I did the cams now just to get a tedious job out of the way.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on July 01, 2019, 07:24:52 AM
On the bearings I'll admit to a bit of laziness. The bearing specs in the ME article for the Bobcat have an error so I went back to Bearings Direct to check what I had ordered last time. As I was there it was too easy to just re-order.

I see what you mean Pete  :thinking: , the article starts by saying they should be 68000 bearings they clearly added one too many zeros at the end  :Doh: Maybe they got confused that it needed an extra numeral as the next bearing they quote is the 61800  :headscratch:

I can't see why you would choose the 61800 over the 6800, they are both open deep ball bearings of the same dimensions  :noidea:

Jo
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 01, 2019, 08:26:39 AM
On the bearings I'll admit to a bit of laziness. The bearing specs in the ME article for the Bobcat have an error so I went back to Bearings Direct to check what I had ordered last time. As I was there it was too easy to just re-order.

I see what you mean Pete  :thinking: , the article starts by saying they should be 68000 bearings they clearly added one too many zeros at the end  :Doh: Maybe they got confused that it needed an extra numeral as the next bearing they quote is the 61800  :headscratch:

I can't see why you would choose the 61800 over the 6800, they are both open deep ball bearings of the same dimensions  :noidea:

Jo

 Jo

Worse than that the  bearing should be a 6801 12x21x5 not 61800 10x19x5  as stated in the ME article

.... and now looking at the invioce I didn't get them from Bearings Direct I've ordered them from Simply Bearings.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on July 01, 2019, 09:29:49 AM
 :facepalm: See what you mean Pete. Looks to be two bearings of 19mm O/D and one of 21mm O/D. I did wonder why in the parts list they had broken the bearings out over two lines and then quoted the same numbers rather than just having one line.

At least they are not too expensive if you get caught by their mistake and have to buy another set  ::)

Jo

Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 02, 2019, 10:33:10 AM
Following along Pete.

Look forward to seeing it in the flesh sometime.

Where are you getting your bearings from? I source bearings from NZ Miniature Bearings if I am not wanting to wait for them to come from Aliexpress sellers

Cheers
Bruce

Bruce

Thanks for the heads up. NZ Miniature Bearings are certainly cheaper and I could well have them by now had I gone to them.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Ian S C on July 02, 2019, 12:53:47 PM
When I buy bearings I use SMP bearings in Carlyle st Christchurch, their prices seem ok.
Ian S C
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 03, 2019, 10:33:07 PM
When I buy bearings I use SMP bearings in Carlyle st Christchurch, their prices seem ok.
Ian S C

Maybe itís the case that in the past NZ suppliers that offered a reasonable price were not obviously online so you couldn't find them. Or they have woken up to the fact that if they want to stay in business, they need to offer their products at an internationally competitive price. Hiding behind, "NZ is a small market" and "Shipping costs to NZ are high" just doesn't work anymore.

In my early days of this hobby I was looking for a something from Vertex. The best price I could get, landed in NZ, was from the UK. Ridiculous when the item was being shipped from Taiwan to the UK and then to NZ. In the end I found the Vertex importer and cut out the middle men, even then it was a similar price to getting it from the UK.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Ian S C on July 04, 2019, 01:16:41 PM
Got my 6" Vertex rotary table with dividing plates and tail stock in Christchurch, and direct from Taiwan about the same time as I got my lathe, also from Taiwan, through Paykels, now I think Blackwoods Paykel
Ian S C
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 05, 2019, 08:51:05 AM
Got my 6" Vertex rotary table with dividing plates and tail stock in Christchurch, and direct from Taiwan about the same time as I got my lathe, also from Taiwan, through Paykels, now I think Blackwoods Paykel
Ian S C

Ian

The heavy stuff I  do purchase locally, lathe and mill. I got my Vertex rotary table direct through the NZ importer. A request to Vertex in Taiwan gave me his details. He didn't have stock, but I ordered anyway. It to only 4 days to arrive to me

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 05, 2019, 08:52:30 AM
A bit of an update

The cams were completed and case hardened with ďCherry RedĒ case hardening compound.

(https://i.imgur.com/udPqeaj.jpg)

Theyíve now been parked ready for the assembly of the camshafts, which Iíll do once Iíve got my head around it and confirmed the firing order and done the timing diagrams. Iíll do it all at the same time.

Next up was the crankshaft. Iím doing a built up crank the same I did with the Bobcat. I forgot to take a photo of the separate parts for the this crank so here they are for the Bobcat.

(https://i.imgur.com/CXQzk1e.jpg)

Hereís the Puma crank with the parts just pushed together.

(https://i.imgur.com/FVCj3SI.jpg)

And assembled with high strength Loctite 680

(https://i.imgur.com/7Ttg1ME.jpg)

I assembled the cranks and webs first to get them into alignment and used the lathe to ensure the nose and tail were in alignment. Next will be drilling the webs and inserting pins to make absolutely sure it all stays together.

The next parts are the four conrods. I started on the blanks while I allowed the Loctite to cure.

I recently saw somewhere a suggestion to use a lathe tool in a fly cutter.  With a CCGT060204 ceramic tip the results were outstanding

(https://i.imgur.com/MjEdCru.jpg)

So now  have four blanks ready for the next stages.

(https://i.imgur.com/gSvVov8.jpg)


Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Roger B on July 06, 2019, 10:35:07 AM
Just catching up with this after having been away on holiday  :)  :)  :ThumbsUp: Looking good  :praise2:  I'm not sure of the need to mill the cams in 1į steps unless you have CNC. I have used 6į steps without problems.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 06, 2019, 10:38:35 AM
Just catching up with this after having been away on holiday  :)  :)  :ThumbsUp: Looking good  :praise2:  I'm not sure of the need to mill the cams in 1į steps unless you have CNC. I have used 6į steps without problems.

Roger

You are probably right, and Malcolm suggested going in 2deg steps, but I wasn't going to try it and then wish I hadn't and have to start again.

It just added a few extra hours to the job as I was making two sets.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Laurentic on July 06, 2019, 12:38:06 PM
Pete, just out of interest, when you loctited the crankshaft together what clearance did you allow between pin/shaft and relevant bore in the web?  I was thinking too much and it's a weak joint, too little and then no space for the loctite?
Chris
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 06, 2019, 10:42:48 PM
Pete, just out of interest, when you loctited the crankshaft together what clearance did you allow between pin/shaft and relevant bore in the web?  I was thinking too much and it's a weak joint, too little and then no space for the loctite?
Chris

Chris

It will be about 1 thou. The tail is 10mm ground silver steel and the hole was reamed. Since being glued I've now drilled the webs 2mm and inserted 2mm pins through all the joints. I did the same for the Bobcat and then for the crank for my 7.25" guage Dart. None of them have been a problem

(https://i.imgur.com/fXPxNXk.jpg)

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Laurentic on July 06, 2019, 10:47:29 PM
Thanks Pete, the 0.001" clearance and 2mm pins were what I was thinking would be about right!  Good to have it confirmed....

Chris
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on July 07, 2019, 12:05:39 AM
Loctite has a product that is used with press fits. I see a lot of people on the forums who think that you have to leave some clearance on fits so as not to scrape the Loctite off during assembly. Loctite claims that you don't need to leave any clearance. I don't leave any clearance on fits (not intentionally anyways) and I've not had anything come apart.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 09, 2019, 08:05:23 AM
Conrods done

Before and after zapping in the sand blaster to remove the tooling marks

(https://i.imgur.com/c1pD3ea.jpg)


(https://i.imgur.com/3q14Lwf.jpg)

Time to roll the dice again and decide what to do next

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Laurentic on July 09, 2019, 12:25:10 PM
Interesting comment Brian, must admit I was in the camp that thought a very wee clearance was required before using loctite.  Do you have the loctite number for press fits, I will get some in!   :ThumbsUp:

Nice piston rods Pete.

Chris
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on July 09, 2019, 01:35:13 PM
Top Pick LOCTITE 620 is a high temperature (450 degrees F), high viscosity liquid retaining compound. Provides a shear strength of over 3,800 psi on steel. Locks and secures metal cylindrical assemblies up to 0.015' diametral clearance. Prevents metal fretting and corrosion. Seals against leakage. Recommended for high temperature retaining of parts with a clearance or interference fit, i,e, retaining bushes, bearings, seals, fans and liners. Requires heat cure to achieve temperature resistance. ABS Approved.
This and Loctite 680
Title: Re: 30cc Flat Four (Puma)
Post by: Laurentic on July 09, 2019, 06:07:33 PM
Thanks Brian, Loctite numbers noted down!!

Chris
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 09, 2019, 08:56:44 PM
Top Pick LOCTITE 620 is a high temperature (450 degrees F), high viscosity liquid retaining compound. Provides a shear strength of over 3,800 psi on steel. Locks and secures metal cylindrical assemblies up to 0.015' diametral clearance. Prevents metal fretting and corrosion. Seals against leakage. Recommended for high temperature retaining of parts with a clearance or interference fit, i,e, retaining bushes, bearings, seals, fans and liners. Requires heat cure to achieve temperature resistance. ABS Approved.
This and Loctite 680

Agreed

The loco cranks were done with 620 and the Puma with 680

One of the benefits of 620 is the slower cure time so you've got a bit of wiggle room. The job doesn't lock up almost immediately on assembly. It gives you time to get it all together and into any alignment jigs you may be using.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 09, 2019, 08:59:49 PM
Interesting comment Brian, must admit I was in the camp that thought a very wee clearance was required before using loctite.  Do you have the loctite number for press fits, I will get some in!   :ThumbsUp:

Nice piston rods Pete.

Chris

Thanks Chris

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 15, 2019, 10:22:19 AM
Well I rolled the dice and, as I had a busy week ahead, decided not to start anything major. So did things like gudgeon pins, cam follower bushes etc. Then the bearings arrived so I was able to do the crank bearing holders.

That allowed a trial fit of the everything Iíve done so far.

(https://i.imgur.com/3ykk9Ak.jpg)

This also allowed me to try out the timing belt sprockets. But that led to a bit of a disaster.

(https://i.imgur.com/NTeqNj4.jpg)

Drilling the crank sprocket to fit the 5mm stub on the end of the crank it fell apart (compare to the good one on the left)

Checking the supplierís catalogue and anything up to 16 teeth is a type 1 on the right are type 2 and they start at 18 teeth. So, it has to be a minimum of 18 teeth on the crank and 36 on the camshafts.

A bit of an update in the CAD and it looks feasible. The order will be placed tonight.

(https://i.imgur.com/kucCFG8.jpg)

Youíll notice Iíve also included an alternative, simpler, exhaust pipe, the ľĒ x 32 spark plugs and a carb sourced from Hobby King.


Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 15, 2019, 10:43:59 AM

A brief video of the trial fit. No pistons yet so it turns quite freely and the conrods can be heard rattling in the bores

eXHSbnImAaQ
Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 22, 2019, 03:41:50 AM
I could do with some help please. These timing belts arenít going to work.  After the 12x24 combination fell apart after drilling the smaller pulley to fit the crank I ordered a set of 16x32 and 18x36 pulleys. Belting Online got them to me in 3 days UK-NZ.

The 16x32 pulleys fit with 160mm belt and the next belt size of 177.5mm has too much slack to be taken up with an idler in the space available. The larger pulley of the 18x36 set were too large.

(https://i.imgur.com/bpgJUiL.jpg)

The other problem will be assembly. With the cams on the camshaft it will be impossible to get the 32 tooth pulleys and belt located on the cam shaft with the 16 tooth pulley already on the crank.

So its back to looking at gears. Iíve drawn it up using metric Mod 1 gears. It all seems to go together OK but with a  bit of underlap on the PCD dimensions. Gears are 12, 24 with a 15 tooth idler.

(PCDís are the dotted lines and O/Dís are the full lines.

(https://i.imgur.com/sjz2XcU.jpg)

I have little experience of gear selection so any thoughts please?

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: bruedney on July 22, 2019, 06:15:34 AM
Pete

Is the reason you can't do the belt because you can't side the belt on once all the pulleys are in place?

If so then do like they do in full scale and only have a lip on the rear of the pulley

Regards
Bruce
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on July 22, 2019, 07:06:20 AM
Can't you just make your own 12T pulley from solid, or rather than pressing the toothed part onto a boss as the bought ones? Or have those two solder or loctite on the flanges for easier tooth cutting.

That's if you really need flanges on the small one with the larger pulleys being so close I doubt you do as the belt won't wander far. Which would make the 16T viable and also easier if you make your own 12T
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 22, 2019, 07:59:15 AM
Thanks for the input guys.

Yes Bruce that's the problem

I had thought about removing the flange and I really don't need to remake anything. I could just Loctite the existing 12T straight onto the crank stub, even with a small flange the bearing, which has a 10mm ID, will go over it as pulley as that is a tad under 9mm dia.

Unless I get more input overnight that says I need the flanges I'll see how it looks in the morning and report back.

Pete






Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 22, 2019, 10:07:35 AM
Why wait until the morning?

This looks like it s going to be feasible as long as the belt stays on the 12 tooth pulley without flanges. What is more it looks a whole lot better than those oversize camshaft pulleys.

(https://i.imgur.com/FmZfCpZ.jpg)


The 145mm belt has just enough slack to allow easy installation and also allow a tensioner to be included. There may even be scope for a 10mm flange on each end and be able to get the bearing off if neccessary.

You will notice that the existing flange is still there. After drilling and reaming there was enough meat left to hold it on. However, it has to go as it is 13mm diameter so if the pulley is held on with Loctite the bearings could not be removed.

Pete




Title: Re: 30cc Flat Four (Puma)
Post by: stevehuckss396 on July 22, 2019, 10:59:58 AM
If it were me I would try to leave the flange on the crank pulley and remove the flanges on the 2 cam pulleys. You really only need the flange on one of the pulleys and it probably doesn't matter which one has it. My thought is to keep the flange on the pulley driving the belt. Unless the cam pulleys are misaligned (highly unlikely) the belt should track around the cams without any trouble.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 22, 2019, 11:40:56 AM
If it were me I would try to leave the flange on the crank pulley and remove the flanges on the 2 cam pulleys. You really only need the flange on one of the pulleys and it probably doesn't matter which one has it. My thought is to keep the flange on the pulley driving the belt. Unless the cam pulleys are misaligned (highly unlikely) the belt should track around the cams without any trouble.

Steve

The problem I have is because of the small dimension of the crank pulley (9mm) the boss came off when I drilled and reamed it to fit the tail on the crank. Take a look at the earlier photos

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: stevehuckss396 on July 22, 2019, 11:30:39 PM
Duh! yep I see it now.  Well you ask for any thoughts on gears. My thought is to put two idler gears either inboard or outboard of the cam and crank gear instead of one in the center. Get the centers spot on so there is minimal slop in the gear train. Make them as small as possible so they wont stick out too far. With a little luck you might even get them on the inboard side of the gears as long as they dont touch in the middle.

 
Title: Re: 30cc Flat Four (Puma)
Post by: Johnmcc69 on July 23, 2019, 12:33:48 AM
 :ThumbsUp:
Nice solution Steve! Would look great too.

 Builds looking great Pete, hope you get everything worked out.

 John
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on July 23, 2019, 01:05:44 AM
It'll be a noisy little rascal with a total gear drive solution. If you want to stay with a timing belt drive, can you cross-pin thru the small timing pulley and thru the end of the crankshaft. If you can, it doesn't matter that the hub came off.
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on July 23, 2019, 07:07:01 AM
Offset Idler, no wthat sounds familiar. Oh yes, that's what I went for on my flat twin version, suppose as they are lightly loaded a plastic idler gear could be used if you think noise will be an issue, hopefully the exhaust should drown out most of the mechanical noise.

(https://img.photobucket.com/albums/v156/jasonballamy/Engineering/Nemett%20Ocelot%20NE15OT/IMAG3002_zpsebkpryci.jpg)
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 23, 2019, 11:10:42 AM
The offset idler was Malcolm Stride's original design. Rather than have two I considered a single would do the job. What I wasn't sure about was the relationship between the gears. Do you design for absolute PCD alignment or is it a case of best fit? Malcolm used a piece of paper to allow the setting the gap between the gears. Jason's photo also has a piece of paper in place.

Having been given the suggestion that one of the flanges can be dispensed with Iím returning to the original use of synchronous belts. More by luck than design the 12x24 pulleys and the 145mm belt seem to fit well and allow the inclusion of a tensioner. The CAD package indicated that a 145mm belt would be too tight. So a synchronous belt is the way Iím going to go for now and Iím now onto making the four cylinder heads.

An example of the benefit of being able to validate thoughts on these forums. It generates a whole lot of good ideas and saves a whole lot of time and cost resulting from any incorrect decisions being made.

Thanks.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on July 23, 2019, 11:51:58 AM
Having an offset idler is standard on model engine designs : think about how far apart it would be necessary to space the cam and crank to fit a gear with a reasonable number of teeth in between and the spacing would be forced by the diameter of the gears rather than to fit the shape  of the engine crankcase.

One thing worth thinking about is making the idler out of brass as it will quieten down the gear chain. And try to make the idler such that it is not an exact multiple or factor of the other two gears as this can cause a hunting tooth  :facepalm: . What you are looking for is that different teeth engage each rotation, which also helps to achieve even wear and quiet running. A good trick is to have an odd toothed gear as the idler  :naughty:

Jo
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 24, 2019, 11:15:53 AM
Jo

Thanks for the advice. I had realised that it was necessary to include an idler and then compromise to be able to use standard gears. If Iíd done a better design job I should have worked out what gears to use a single central idler and then adjust the lateral position of the two camshafts so everything lined up properly. The odd number tooth for the idler was new to me. Belting Direct do gears and they have steel, brass and Delrin gears available. I guess a Delrin gear would be quiet but would they work in this application?

I was coming to a similar conclusion about compromise when using synchronous belts. The next available sizes for the crank pulley, after 12t was 16t and then 18t. The corresponding 32t and 36t pulleys for the cams were getting too large to look neat. The suggestion of using a flangeless pulley appears to be the way to go. We'll see and if it doesn't a switch to gears could be on the cards.

All good stuff thanks

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 25, 2019, 10:15:35 AM
Iím working through the various stages of making the cylinder heads. Iíve got to the passages for the inlet and exhaust ports. They are angled at 15deg. I was faffing about with protractors and digital angle gauges when I had an inspiration that the valve guides would be a readymade sine bar.

They are 12mm apart so the offset needs to be 12x sin(15) = 3.105mm. I used a slip gauge but a 3.1mm drill shank would do it.

(https://i.imgur.com/OvyotRA.jpg)

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Roger B on July 28, 2019, 07:57:05 AM
I solved a similar problem using my rotary table. In this case the central bore of the RT was the same as the valve guide holes so I didn't need to make an adaptor and just used a length of 6mm silver steel. With the RT centred I could Slip each valve guide over the 6mm ss, set the angle and machine the port.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 29, 2019, 11:37:43 AM
Roger

Very good; as they say 'many ways of skinning cats' I was following Malcolm Strides approach and was not happy with it. I can't remember how I did it 6 years ago, then had the epiphany. I later realised Iíd done similar things when machining things like connecting rods.

A bit of an update. Last week was spent doing the four cylinder heads, many different sequences were required so they took a bit of time. They were finished over the weekend so couldnít resist trying them out.

(https://i.imgur.com/W6Eub2f.jpg)

The bags contain various other parts that Iíve made on the way. I find doing a few small parts, here and there, helps reduce the tension that occurs when doing the more complicated stuff. It also means that over time everything things get done before it is required.

The piston rings were made when I did the Bobcat six years ago. I had never done piston rings before and expected problems, so made a few.  My concerns were unfounded and only used four of them so ended up with a few spares.

Iíve been updating the CAD and now have the approach to the hall sensors sorted. I plan to use two of the RCExel type, twin cylinder CDI units. So will need two hall sensors that trigger alternatively twice each half rev. Following Malcolmís approach, Iíll have two magnets on a disc for each unit and a disc on each cam. Each disc will be 90deg out of phase with the other so 4 trigger events on each rev alternating between the two units.

(https://i.imgur.com/NsfR4e3.jpg)

The vertical bar just behind the crank will have a sensor set in the left and right hand edges.

When I did the Lynx I ended up doing a home made ignition system with a PICmicro controller that enabled the advance curve to be set on a running engine. In the fullness of time I may resurrect that project for a 4 cylinder version

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: bruedney on July 29, 2019, 09:53:03 PM
Looking good Pete

 :popcorn: :popcorn:

I have had some time off so I have got back to doing some work on my single cylinder IC engine. Had it running on Shellite  :whoohoo:

Yesterday afternoon was spent making a base whilst I await a smaller spark plug to come (ordered the wrong Rcexl unit).

Cheers
Bruce
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 30, 2019, 07:24:24 AM
Looking good Pete

 :popcorn: :popcorn:

I have had some time off so I have got back to doing some work on my single cylinder IC engine. Had it running on Shellite  :whoohoo:

Yesterday afternoon was spent making a base whilst I await a smaller spark plug to come (ordered the wrong Rcexl unit).

Cheers
Bruce

Bruce

Thanks

What plugs were you planning to use? The RCexl plug caps can be changed. I've used 1/4x32 on all my engines and have some of the larger plug caps spare. I'm not sure if they are CM6 or 14mm but give me a call and maybe I can help.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: bruedney on July 30, 2019, 07:27:54 AM
Thanks Pete

I have a CM6 spark plug but a NM8 (1/4 x 32 I think)) connector on the Rcexl unit. If you have a CM6 connector that would be great.

Unfortunately I am back at work tomorrow but I will touch base with you sometime to catch up.

Bruce
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on July 30, 2019, 08:52:41 AM
Thanks Pete

I have a CM6 spark plug but a NM8 (1/4 x 32 I think)) connector on the Rcexl unit. If you have a CM6 connector that would be great.

Bruce

I have one of each of the larger type of caps.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 02, 2019, 07:44:41 AM
Iíve been working on the cam belt and ignition triggers. Much as shown in the CAD diagram. The one thing that I havenít done in CAD is the belt tensioner. The CAD thinks the 145mm belt is too short but that isnít the case with the belt Iíve purchased.

I had drawn up a tensioner but with bearings it looked too large against the overall size of things. Then one of those ďletís try thisĒ moment. A stack of 630ZZ bearings that were to be used as the tappet bearings for the Bobcat did the job and with a long 3mm cap head bolt it went straight one of the existing holes in the rear bearing holder.  Job done.

(https://i.imgur.com/bJajb2c.jpg)

The next job is to assemble the two camshafts but some guidance from you please. Given this layout:-

(https://i.imgur.com/WWEPVcx.jpg)

Do I make the firing order 1,2,3,4 or 1,3,4,2 or is there any other alternative? What are the reasons for selecting one over the other?

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on August 02, 2019, 08:21:05 AM
The firing order is defined by the cam lobes  ;)

My Seal should fire 1-2-4-3 or 1-3-4-2 depending on if it was cut moving the pointer clockwise or anticlockwise on the cutting jig

Jo
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 02, 2019, 08:43:30 AM
The firing order is defined by the cam lobes  ;)

My Seal should fire 1-2-4-3 or 1-3-4-2 depending on if it was cut moving the pointer clockwise or anticlockwise on the cutting jig

Jo

Jo

I've not assembled the camshafts yet, I have 8 separate cams that are to be loctited to the shaft. So I can make it what I want. I thought I'd check with the experts before I committed.

Given the crank journals are shared and 180deg apart I can either fire the front pair (serially) then the rear pair (1,2,3,4) or the left pair followed by the right pair (1,3,4,2).  I guess I'm looking for the solution that is likely to be the smoothest running.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: bruedney on August 02, 2019, 09:11:00 AM
Hi Pete
I think you have your cylinder numbering wrong. Since it seems your crank config is more like a V4 than a boxer I would say (after looking at google image search) that the firing order should be 1, 3, 4, 2 but the cylinder number should be like is indicated here http://www.woiweb.com/index.php/Firing_order (http://www.woiweb.com/index.php/Firing_order)

Cheers
Bruce
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 02, 2019, 10:23:07 AM
Hi Pete
I think you have your cylinder numbering wrong. Since it seems your crank config is more like a V4 than a boxer I would say (after looking at google image search) that the firing order should be 1, 3, 4, 2 but the cylinder number should be like is indicated here http://www.woiweb.com/index.php/Firing_order (http://www.woiweb.com/index.php/Firing_order)

Cheers
Bruce

Bruce

My original cylinder numbering was like an integrated circuit going anti-clockwise from #1. I realised that could be confusing to some so for the purposes of the question used the convention in my diagram. For now I'd like to understand whether option A (1,2,3,4) or otion B (1,3,4,2) would be best dynamically. After that any numbering scheme can be adopted but will still run in the preffred order.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Roger B on August 02, 2019, 01:42:57 PM
With your manifold design there shouldn't be much difference. If you had one carb feeding 1 and 3 and one feeding 2 and 4 the first option would be better as it would give even intervals between suctions. The same would apply if the exhausts were joined rather than separate.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 02, 2019, 11:00:57 PM
Roger

Thanks. The intake/exhaust configuration is something that I had not considered. I think making it a twin carburetor design would be a step too far.

So given the current design of a single carb and manifold you think either option would be acceptable? If thats the case then going the 1,2,3,4 route would mean two camshafts with the same configuration and the two sets of cams set 180deg out.

Which is as Malcolm's original design.

(https://i.imgur.com/JmvYYNA.jpg)

The two camshafts will then be set up with the left hand camshaft leading the right by 90deg, which is 180deg on the crank. That keeps it simple.

I think that will be correct but I will check my assumptions

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 03, 2019, 12:41:53 AM
Well that didn't take me long to find out I was wrong. I was trying to reconcile why the cam layout for the left hand (1,3) cylinders would be the same as Malcolms Bobcat design when the crank for the two adjacent cylinders on the Puma are 180deg apart.

Back to the start with the crank diagram and my proposed firing orders were incorrect (* indicates firing cylinder)

(https://i.imgur.com/6F484Sk.jpg)

So now it is 1,2,4,3 or 1,3,4,2 either way adjacent cylinders will fire one after the other.

I'll eventually get my head around all this and get the cam shafts assembled.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 03, 2019, 01:09:28 AM
Four cylinder automobile engines are timed 1-3-4-2. There must have been some logic behind this. Rotary engines has sequential firing order.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 03, 2019, 03:00:10 AM
Four cylinder automobile engines are timed 1-3-4-2. There must have been some logic behind this. Rotary engines has sequential firing order.

And thats from a VW man, also flat 4's, so let's go that that way.

Thanks Brian.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Bluechip on August 03, 2019, 10:48:25 AM
Ditto for Subaru it seems ..

https://www.bing.com/images/search?q=subaru+firing+order&qs=HS&form=QBILPG&sp=1&sc=8-0&cvid=20ABD881D899438ABC41129F89FFB1D9

D.
Title: Re: 30cc Flat Four (Puma)
Post by: Ian S C on August 03, 2019, 03:06:57 PM
Lycoming and Continental 4 cylinder  aero engines are 1342.
Ian S C
Title: Re: 30cc Flat Four (Puma)
Post by: Admiral_dk on August 03, 2019, 07:53:48 PM
Quote
Lycoming and Continental 4 cylinder  aero engines are 1342.

Yes - but they have a normal flat-four crankshaft layout - this one is VERY different, or as stated earlier - it is a V4 that has been flattened from 90 to 180 degrees without changing the crank.
This completely excludes any normal firing order !!!!.... and it also results in an engine that should vibrate quite a bit more - that said, it is also a much easier crank to make ....

I still expect it to give you great satisfaction when it runs  :ThumbsUp:

Best wishes

Per
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 04, 2019, 03:01:16 AM
Thanks for all your input, 1,3,4,2 it is.

I've now sorted the cam assembly and glad I took the time to get my head around it and model in CAD. Only 1/2 an hour ago I realised that the table of angles for the rotatry table setup had one of the inlets lead the exhaust rather than lagging. (Of course they don't when running but as the start point of assembly is an exhaust cam the  table is rotated clockwise and the inlet is 102.5 degree behind it.)

(https://i.imgur.com/1SLgmJK.jpg)

The table and the assembly now reconcile

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 04, 2019, 09:50:39 AM
Camshafts assembled and installed

QgefE1PddUI
kC5fpwutvds
Tommorrow I'll do the pistons. I'm not expecting them to be too much of a problem.

I'll admit it now, I'm going to cheat. My Bobcat and Lynx took ages to get running. When Brian did his flat twin, based on Malcolms design, he got it going just about his first try. I put it down to him using O rings.  I'm convinced the compression on my engines has improved just by them sitting on the shelf. I believe the, once new, rings have normalised over time improving their fit.

So, I'm going to try 1x20 metric O rings as they will go straight into the ring grooves. I can then always go back to rings, I have them already.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on August 04, 2019, 11:20:41 AM

I'll admit it now, I'm going to cheat. My Bobcat and Lynx took ages to get running. When Brian did his flat twin, based on Malcolms design, he got it going just about his first try. I put it down to him using O rings.  I'm convinced the compression on my engines has improved just by them sitting on the shelf. I believe the, once new, rings have normalised over time improving their fit.

So, I'm going to try 1x20 metric O rings as they will go straight into the ring grooves. I can then always go back to rings, I have them already.

Pete

I know O rings are commonly used on the pistons of steam engines but are not that common in i/c engines. Which O ring materials and hardness works best? Do you use nitrile or viton or PTFE O rings or something else?

What works best? What does the team think?

Mike
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on August 04, 2019, 12:15:19 PM
The last couple of IC engines that I have made were both fitted with single Vitron rings. Though both are relatively slow runners.
Title: Re: 30cc Flat Four (Puma)
Post by: Allen Smithee on August 04, 2019, 12:25:26 PM
Four cylinder automobile engines are timed 1-3-4-2. There must have been some logic behind this.

Think of it as 3-4-2-1, which is "inner-outer-inner-outer" torque pulses on the crank. This is less likely to set up torsional resonances in the crankshaft (at least that's what it says in an automotive engineering textbook on my bookshelf).

AS
Title: Re: 30cc Flat Four (Puma)
Post by: fumopuc on August 04, 2019, 02:23:18 PM

I'll admit it now, I'm going to cheat. My Bobcat and Lynx took ages to get running. When Brian did his flat twin, based on Malcolms design, he got it going just about his first try. I put it down to him using O rings.  I'm convinced the compression on my engines has improved just by them sitting on the shelf. I believe the, once new, rings have normalised over time improving their fit.

So, I'm going to try 1x20 metric O rings as they will go straight into the ring grooves. I can then always go back to rings, I have them already.

Pete





I know O rings are commonly used on the pistons of steam engines but are not that common in i/c engines. Which O ring materials and hardness works best? Do you use nitrile or viton or PTFE O rings or something else?

What works best? What does the team think?

Mike



Hi Mike,
my Hoglet engine is running with Viton O-rings, one at each cylinder, since the first fire up.
I could not believe that it will work, but so far without any issues.
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on August 04, 2019, 04:17:15 PM
Hi Mike,
my Hoglet engine is running with Viton O-rings, one at each cylinder, since the first fire up.
I could not believe that it will work, but so far without any issues.

The last couple of IC engines that I have made were both fitted with single Vitron rings. Though both are relatively slow runners.

Thanks guys,

That's two positive votes for Viton O ring piston rings.

The next important question is the dimensions of the piston groove. Should the depth of the groove equal the width and equal the O ring cross section? Or should the groove be shallower to squeeze the O ring?

Mike
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on August 04, 2019, 04:39:45 PM
Shallower than the ring section but also wider so it can take on a slight oval shape, I use Model Engineers Handbook for the groove sizes as they are less than you will find quoted on the ring makers sites which will give a good seal but far too much drag. reeves paper catalogue also has a similar model specific chart.
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on August 04, 2019, 05:44:44 PM
Thanks Jason,

I have found the groove dimensions you refer to in Section Eleven of 'Model Engineers Handbook' by Tubal Cain, published by Argus Press. I do not have the Reeves catalogue to compare.

Mike
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 04, 2019, 08:52:36 PM
Thanks for the validation. I was expecting some negative responses however this area of model engineering doesnít suffer from that habbit as much as some.

As the grove for 1x20 O rings is similar to that required for CI rings I can afford to experiment. I had expected to need to make two sets of pistons but thatís now not the case. My supplier is only 10 mins away from the house and they have stock of them in Viton. Iíll be over there this morning once the lemmings have gone to work.

My understanding of the grove width is that it needs to be slightly wider than cross section of the O ring. That then enables the pressure to get behind the whole face of the ring and distort it against the base of the groove and the wall of the cylinder. With a 4 stroke that will also reduce friction, to some degree, for75% of the time.

https://www.fluidpowerworld.com/how-does-an-o-ring-seal/ (https://www.fluidpowerworld.com/how-does-an-o-ring-seal/)

Also, for that reason, only one ring should be required. If the first ring is doing its job the second one becomes redundant.

Anyway, nothing ventured nothing gained. There is an element of experimentation and certainly learning in this hobby.

Regards

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 05, 2019, 01:16:31 AM
I don't get too deeply into metric world, but I have great success with Viton O-rings as piston rings on my i.c. engines.--So--Here is what works for me. I use a "nominal" 1/16" (1.57mm) cross section o-ring. The REAL cross section is actually 0.070" (1.78mm). I cut the piston groove 0.094" (2.39mm) wide x 0.056" (1.42mm) deep. The only thing to be aware of, is that there will be more "drag" as the piston moves in the cylinder than if you use cast iron rings. (This is irrelevant unless you are making a "hit and miss" i.c. engine). That is why I have purchased cast iron rings for use on the current vertical hit and miss engine that I am building. I have about 5 or 6 "hit and miss" engines that I have built, and they all have viton rings, and I have never been able to get any of them to "hit" once, then go thru a number of "miss" cycles before "hitting" again.  I deeply envy all those who have built model hit and miss engines which actually run the way there full sized brothers do. (My engines all have to "hit" three or four times before building up enough speed to go into "miss cycles", and when they do, the "miss" cycles never last very long because of the "drag" effect.
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on August 05, 2019, 11:16:27 AM
Thanks Brian,

Those numbers give a real live working design case.

Actual O ring diameter = 0.070".      Grove width = 0.094",       Groove depth = 0.056".

We can make those measurements dimensionless (expressed as a percentage) so that other sizes of O ring groove may be designed from your data.

Based on your information:  Grove width is 34% wider than the measured O ring diameter. Groove depth is 80% of the measured O ring Diameter. The cross section Area of the ring groove is 36% larger than the O ring cross section area, which gives the O ring plenty of room to compress and move about.

If we allow say 0.002" clearance for the piston in the cylinder, the O ring will be squeezed down to ( 0.058")  73% of the O ring diameter, thats a 17% nip.

My old company had a 'rule of thumb' for O ring fits. They recommended 20% for a static seal and only 10% for a dynamic seal. But that was for water pressure applications, NOT I/C engines.

If that holds true for I/C engines, then you should be able to use a groove 0.005" deeper and gain the benefit of lower static friction (lower drag). 

However Brian, your dimensions are proven to work, so why fix them?    :stir:    Just saying

Cheers

Mike


Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 08, 2019, 08:30:23 AM
Pistons done and assembled on their conrods. The piston on the right has the O rings fitted. I decided to use 2. They are pretty small.

(https://i.imgur.com/Y45DQYQ.jpg)

Installed in the crankcase

(https://i.imgur.com/kWrL3ED.jpg)

Time to hone the cylinder bores. Rather than risk distorting the liners in the chuck I've clamped them in the cylinders with washers

(https://i.imgur.com/A4eTnyZ.jpg)

And cylinders installed

(https://i.imgur.com/JqO7vni.jpg)

(https://i.imgur.com/pYJX7Bh.jpg)

JdfKjWFKrdk
Next up is the rockers, valves and all the other fiddly bits that go with that. I've made a start on the rocker supports.

As an aside; I showed engine at the club night last night and mentioned the lathe tool as a fly cutter. I made a video of it today

A skim cut and then 0.5mm cut at 1800RPM using CCGT0 60204 Aluminium cutter blade insert in a lathe tool.

roKUtbEgzpM
Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on August 08, 2019, 01:06:02 PM
I think you need to modify the top of the crankcase to incorporate a viewing window otherwise those red conrods will be lost to most :LittleDevil:
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 08, 2019, 01:08:47 PM
Absolutely stunning work. I am enjoying this build.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 08, 2019, 09:34:40 PM
Thanks Jason and Brian

A window has crossed my mind a number of times, including last night. I have some polycarbonate sheet that would be perfect. I have even considered replacing the sump with a polycarbonate sheet and running it upside down.

Lubrication would be the issue as the window would soon get covered in oil.  A dry sump and pump was suggested by Bruce but without any oilways built in it would need to be spray lubrication and back to being messy.  Then it could be completely dry and lubed up before running like we do with our locos and Brianís  twin.

However, this should run at a minimum of 1000RPM so there wouldnít be much to see when it is running.  It could be a case of Ďnever say neverí, as generally with these engines after the fun of getting them built and running they tend to go on a shelf and rarely, if ever, get run again. Thatís what happens to mine.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on August 09, 2019, 07:45:03 AM
Why did you paint (I assume it is paint) the con rods Pete? And what did you paint them with?

I am worrying about the paint coming off, as I saw this happen many years ago when one of our forum members was measuring the speed of one of our torpedo engines :-X

Jo
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 09, 2019, 10:47:09 PM
Why did you paint (I assume it is paint) the con rods Pete? And what did you paint them with?

I am worrying about the paint coming off, as I saw this happen many years ago when one of our forum members was measuring the speed of one of our torpedo engines :-X

Jo

Jo

Good question. I took the view that I'd do a bit more with this engine rather than leave it 'naked'. They look great when they are first done but quickly oxidise and don't look to good. I use epoxy enamel. I dries hard and is durable. It seems to be as close to powder coating you can get without powder coating.

http://www.wattyl.co.nz/en/find-the-right-product/exterior/Metal/Topcoat/WattylKillrustEpoxyGlossEnamel.html (http://www.wattyl.co.nz/en/find-the-right-product/exterior/Metal/Topcoat/WattylKillrustEpoxyGlossEnamel.html)

Using the rattle cans I've done all my locos with it and on steel it doesn't need primer, so lazy painting. On brass, copper, aluminium the etch primer is good. The crankcase is currently just primer.

As for the paint coming off of a torpedo motor, I'd guess they run at far higher speeds I'd ever expect to achieve. I don't think its going to be a problem here.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Laurentic on August 10, 2019, 01:06:59 PM
Going back to Brians post No.92, the figures/dimensions Brain gives for O ring grooves are almost exactly as detailed on this website https://www.polymax.co.uk/media/documents/Polymax_O-ringen_Guide.pdf by a supplier, which shows Brian is spot on with what works! :ThumbsUp:

Chris

PS I would like to try epoxy gloss enamel, but Wattyl stuff is not available it seems in the UK - anyone have an alternative?
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 10, 2019, 01:30:30 PM
I have built glass viewing panes into engine crankcases. You can see fine until you start the engine. With no oil in the crankcase, all you see is a blur when the engine is running. With oil, you can't even see the blur.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 10, 2019, 10:48:57 PM

PS I would like to try epoxy gloss enamel, but Wattyl stuff is not available it seems in the UK - anyone have an alternative?


Laurentic

Wattyl are part of the Valspar Group maybe there is a similar product but under another brand in the UK.

Dulux do something similar, but again AU/NZ https://www.dulux.com.au/products/31A (https://www.dulux.com.au/products/31A)



I have built glass viewing panes into engine crankcases. You can see fine until you start the engine. With no oil in the crankcase, all you see is a blur when the engine is running. With oil, you can't even see the blur.


Brian

Much as I expected would happen.  With oil you can't see the blur but with the engine stopped can you see anything? Was it worth the effort to include a window?

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 10, 2019, 11:46:41 PM
No
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 11, 2019, 07:43:06 AM

No


Well thatís one job off the list then. No window.

When I was showing progress at the club monthly meeting somebody commented that the engine was smaller than they expected it to be. After this weekendís activity I have to agree with them. The rockers are tiny.

(https://i.imgur.com/LP87PMc.jpg)

When I did the Bobcat I was used to doing small stuff, having worked on a 3.5Ē gauge loco. I then went to a 5Ē guage loco and more recently have been working on 7.25Ē gauge projects. You donít realise that you get conditioned to the size of your work.

I guess it the valves and springs are next.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 14, 2019, 09:56:56 AM
Iíve been doing the valves; I need 8 so it was going to be a longish job. I started by making them from 10mm stainless bar stock. A lot of machining and wasted material to get it down to the 8mm for the head and 3mm for the shank. Even when using a centre in the tailstock the 3mm was eluding me, either 2.98mm and too loose in the valve guides, or 3.02mm and oversize. Even with a new carbide tip when it got close to size the finish wasnít that good. It was going to take ages and no doubt several rejects. I decided to go the fabricated route. I wasnít sure if it was an accepted approach but a check of a few posts on here and found it was.

At the top 3 failed attempts from solid, below 9 heads and 10 shanks. It was 10 heads but one decided to eat my 3mm bottom tap. So only one spare rather than 2.

(https://i.imgur.com/UiDcviR.jpg)

Silver soldered the heads to the shanks. Good penetration of the solder so I was happy with that.

(https://i.imgur.com/Hj1WwCX.jpg)

The heads were oversize (10mm) so they could be machined down to size after the soldering to ensure concentricity.  Piston and piston rod style

(https://i.imgur.com/hIneB62.jpg)

I used my Deckel-alike tool grinder, which was contorted into service using the side of the diamond disc to grind the 45deg bevel

(https://i.imgur.com/P50LoUX.jpg)

A bit of a final polish with some well-worn 600 grit paper and job done.

(https://i.imgur.com/0f06l1E.jpg)


Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Roger B on August 14, 2019, 11:32:57 AM
I make my valves from stainless steel screws/bolts. This reduces waste and time. The valves shouldn't be too tight in the guides, especially for the exhaust valve, as the valve will tend to run hotter than the guide.
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 14, 2019, 12:38:11 PM
Nice job on the valves. A bit more complicated than making them from a single piece, but you do whatever it takes. I envy your ability to grind the valve faces. I have to turn mine, and it always leaves micro ridges I have to lap out.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 14, 2019, 09:37:22 PM

I make my valves from stainless steel screws/bolts. This reduces waste and time. The valves shouldn't be too tight in the guides, especially for the exhaust valve, as the valve will tend to run hotter than the guide


Roger

Point taken about the exhaust but concern was the inlets leaking too much when the cylinder doing the inlet stroke is trying to draw fuel/air mux through the carb and additional air is coming in through the valve stems. If you look at the drawing the length of pipe run between the carb and the 4 inlets ports is relatively long. I'm just expecting problems in that area so doing what I can to mitigate.


Nice job on the valves. A bit more complicated than making them from a single piece, but you do whatever it takes. I envy your ability to grind the valve faces. I have to turn mine, and it always leaves micro ridges I have to lap out.---Brian


Brian

Thanks

On balance the fabricated valves were quicker, or at least had a better yield, so proved quicker. As I've said before I'm not happy with the prospect of repetitive work and having to make more if one failed would only result in quality and yield falling away as I got more downhearted. With fabrication the shanks were relatively easy and quickly produced. The heads were a bit of a problem with tapping. I broke a tap, which slowed the job down as caution crept in. The soldering took less than 20 mins and once Iíd worked out the grinder configuration the grinding didnít take much longer.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 21, 2019, 09:36:09 AM
Itís been a while since my last post and a bit of a challenge. I saw doing the remaining parts for the valves as a series of relatively simple parts that could be knocked out in quick succession.

How wrong I was. I think I started with the wrong mindset and consequently simple it wasnít. There was also a degree of cockiness and ďIíve done these beforeĒ. For example, after Iíd done the valve supports, I was checking Malcolmís notes about something else and realised they should have been done in steel, not aluminium. So, they had to be done again. I recall wondering why they werenít bushed when I was doing them in aluminium but just pressed on. I later found that the rockers should also be steel. Malcolm had originally planned to use aluminium but changed to steel as he thought aluminium wouldnít be up to it. Iíve done mine on 7075 tool plate so Iím not doing them again.

One Ďproblemí I have had is getting things to fit. It all goes together but everything has been tight so it has taken time to get things to a working fit. Yesterday it was the cam followers getting them down by 0.0004Ē to get them to fit into the guides which I had reamed with a D bit made from the same material. They had swelled slightly on hardening 0.2491Ē was OK but 0.2495Ē was tight, 02497Ē was just about a press fit.

Anyway, some pictures of where Iím at

(https://i.imgur.com/Vu0ovTb.jpg)


(https://i.imgur.com/WWggWUv.jpg)


(https://i.imgur.com/605PnI2.jpg)


(https://i.imgur.com/tpzGqTp.jpg)


(https://i.imgur.com/bdXsGbM.jpg)


And a brief video

ZL2BQHfMK4g
Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Bluechip on August 21, 2019, 09:48:17 AM
Private video here, no can see  .....  :noidea:

Dave
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 21, 2019, 10:05:40 AM
Private video here, no can see  .....  :noidea:

Dave

Dave

Please try again

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Bluechip on August 21, 2019, 10:39:04 AM
Private video here, no can see  .....  :noidea:

Dave

Dave

Please try again

Pete


Yep!   That works fine now.  Very interesting build, been following discretely ..  :)

Dave

Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 23, 2019, 08:50:37 AM
Iíve had the usual problem of getting the valves lapped and being able to test them. Lapping and reassembling on the cylinder and using the piston to check it they had sealed was getting a bit tedious. Taking them on and off coupled with knowing what properly lapped should look like.

I then had a bit of a brainwave. I already had a jig for holding the head in the rotary table to machine the curved heads. That was Malcolm recommended approach.

(https://i.imgur.com/CUQxjy0.jpg)

A bit more machining to accommodate the valves and a port to attach the airline.

(https://i.imgur.com/yKHuLOV.jpg)

Mounting the head and applying pressure from the airline allowed me to lapp the valves under pressure so it was pretty obvious which one was leaking and when the leak was resolved. The brass plug seals the spark plug hole.

(https://i.imgur.com/lntFEci.jpg)

When they went back on the heads and the piston pushed against the closed valves it was clearly a marked improvement.

Question Ė what degree of sealing am I to expect with these valves? Should they seal completely, say similar to a ball bearing clack valve? I'd guess that is ideal but is it really achiveable? Do they bed themselves in once the engine is running?

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Roger B on August 23, 2019, 09:58:57 AM
You should aim for a complete seal. It will make the first starts easier and also the valves may not bed in and the sealng can become worse due to carbon build up.
Title: Re: 30cc Flat Four (Puma)
Post by: Admiral_dk on August 23, 2019, 11:29:55 AM
I can tell you that any valve leak on a full size engine will destroy the valves and seats - and the more leakage the faster the destruction  :zap:

Considering how much compression preasure will be lost that smaller the engine is, the more difficult it will be to start the engine / get it to run continuesly ....
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on August 23, 2019, 11:38:50 AM
I tend to just give my engines a quick suck on the exhaust or carb holes and if there is reasonable resistance that's OK, never done a pressure test but expect it may leak away over a minute or so. All my engines seem to run OK.

With the soft bronze seats you will get then settling in and a better seal
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on August 23, 2019, 11:41:07 AM
Iíve had the usual problem of getting the valves lapped and being able to test them. Lapping and reassembling on the cylinder and using the piston to check it they had sealed was getting a bit tedious. Taking them on and off coupled with knowing what properly lapped should look like.

When they went back on the heads and the piston pushed against the closed valves it was clearly a marked improvement.

Question Ė what degree of sealing am I to expect with these valves? Should they seal completely, say similar to a ball bearing clack valve? I'd guess that is ideal but is it really achiveable? Do they bed themselves in once the engine is running?

Pete

Hello Pete,

Yes you should always aim to achieve perfectly sealed valves. It is difficult and time consuming but it can be achieved. Your test rig is an excellent way to identify any leaky valve seats.

I had 36 valves to lap on the Bristol Jupiter, which gave me plenty of opportunity to experiment and find a good quick way to seal each of the valves. Each of the 36 valves was lapped in and tested with a vacuum leak tester. The fine valve grinding paste supplied for auto restorers was simply too course for a small model engine. So,  I started by using Autosolv metal polish, This proved to be excessively time consuming. I next tried 600 grit silicon carbide, which was much quicker but did not give the best leak test results, the valve seats were a dull matt finish. Finally, I obtained some 1200 grit green silicon carbide powder from a gem stone polisher. The ultra fine powder was made into a paste with mineral oil and a little white spirit. The ultra fine abrasive powder worked well, each of the valves was lapped reasonably quickly and all were able to pass my full 30 second leak down test.

You can read the full story of my valve lapping adventures if you go to Reply #104 of http://www.modelenginemaker.com/index.php/topic,7559.100.html

Hope this helps

Mike
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 23, 2019, 12:48:14 PM
Thanks for the feedback.

I'll admit that the Holts stuff is too course and because of that it has been parked at the back of the shelf for 6 years or so. It is  the 'fine' paste and I only used only the dust and fluid as the heavy particles had settled. I'll give  it another go tomorrow.  I have tried in the past 'Brasso' but that is too fine but, like Vixen, I do have Solvol Autosol so that may be the way to go for now. Finding some 1200 grit from a gemstone polisher may be a problem in the short term. (I'll check the link)

On the plus side the 1mm section Vition O rings replacing the 1mm CI rings do seem to seal OK so that's one variable dealt with for now.

(EDIT: just has a look at Mikes link to his Jupiter. I do have a seat cutter, I think to a George Britnell design (I could be wrong) that I made last time. I should give that a go but it does shave a lot off the seats and I'll admit I was reluctant to take a step to far)


Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on August 23, 2019, 01:06:22 PM
Hello Pete

If you do an e-bay search for '1200 grit powder', you will get hits from all over the wold. UK, USA, China, Ukraine etc. It's often used by gem stone polishers.

It may be better to wait for the good stuff to arrive by post than to carry one with the wrong stuff.

If the valves are almost sealing, it may be better not to use the seat cutter again, just use the 1200 grit made into a paste with a little oil.

Mike
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 23, 2019, 01:33:37 PM
I do the same test by modifying a sparkplug to take an air hose and pressurize the cylinder.--Brian
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on August 23, 2019, 01:55:47 PM
Hello again Pete,

If you cannot easily find any 1200 grit  abrasive powder, it's not a problem.

Just PM me with your postal address and I will air-mail a small quantity down to you.

Cheers

Mike
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on August 23, 2019, 02:23:49 PM
I tend to use 1000g SiC with a drop of oil as the carrier.

Always prefer to try and do my valve guide holes and then taper turn the seats in one setting on the lathe and have not had to use a seating tool on any done that way.

Only one I did have problems on was where the valve seat was on the far side of a cylinder accessed through the inlet of the CI cylinder.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 23, 2019, 10:45:39 PM
Hello Pete

If you do an e-bay search for '1200 grit powder', you will get hits from all over the wold. UK, USA, China, Ukraine etc. It's often used by gem stone polishers.

It may be better to wait for the good stuff to arrive by post than to carry one with the wrong stuff.

If the valves are almost sealing, it may be better not to use the seat cutter again, just use the 1200 grit made into a paste with a little oil.

Mike

Mike

Thanks for the offer, 100grams on order from China. China has free shipping and the USA charge more for the shipping than the product

regards

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 23, 2019, 10:56:30 PM
Pete--I use 600 grit aluminum oxide paste for lapping my valves. If I think the 600 grit isn't going to do it, I lap first with 400 grit, clean everything well, then use 600 grit. I have never used anything as fine as 1200 grit.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 23, 2019, 11:51:59 PM

Pete--I use 600 grit aluminum oxide paste for lapping my valves. If I think the 600 grit isn't going to do it, I lap first with 400 grit, clean everything well, then use 600 grit. I have never used anything as fine as 1200 grit.---Brian


Brian

I have been using Holts fine paste; however, I can't find any technical data that tells me the grit size. As I'm almost there I'm hoping that the finer paste will do the trick.

I think the key is patience. I had on cylinder that was markedly worse than the other three. After I used my pressurised jig it was the best, so I did the others which then came out better. So back around the buoy again. Thatís todays job while I wait for the 1200 grit to arrive from China. Which could take a few weeks. (I did think that if I ordered aluminium oxide powder it could attract some attention at customs  ;D)

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on August 24, 2019, 01:27:33 AM
I think you'd have been okay with the feds. Aluminum oxide is a widely used and distributed lapping compound. It is sold premixed with either a heavy grease or wax. (I'm not sure which). When I first started building i.c. engines, I bought a small jar of "valve grinding compound" from an automotive supplier. Compared to 400 or 600 grit lapping paste, the particles in that automotive stuff was like boulders. It was no good for model engines. I have also heard of people using BonAmi scouring powder and toothpaste. The problem with the really fine compounds is that they don't cut enough to properly lap lathe turned valves into lathe bored seats. This is all stuff learned by experience. I have about a dozen steam engines and 20 different i.c. engines.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 24, 2019, 10:29:31 PM
Brian

As I said in your thread you always seem to be successful with your engines and thatís no doubt after the experience of making twenty. This is my third and the other two ran but I wouldn't say they were fantastic runners. They took me ages to get them to start and even when they were runners the throttle needed to be opened quiet carefully otherwise they stalled.

I'm hoping for better results this time. The fit of the pistons, using O rings rather than CI and spending more time lapping the valves, the engine seems to have better compression at this point than my early attempts. That, coupled with four cylinders rather than one or two, Iím hoping that at least one cylinder will play ball and its mates follow along.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Stuart on August 26, 2019, 04:36:26 PM
Any one tried ďTime saverĒ ?

I use it to bed in bronze bearing , big ends and sutch

Yellow for non ferrous green for ferrous

The beauty is that itís pumice based and the longer itís used the finer it gets

Used in industry to bed in large gear boxes you bout have to dismantle/flush out

Itís also in the breakin oil in your car from new

Not connected with the firm at all just a user
Stuart

Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 27, 2019, 07:47:30 AM
Hi

Loosing the plot here making edits to my recent post I have over written this post. So the original post here has gone missing. Sorry about that

Making mistakes seems to be getting worse recently.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Stuart on August 27, 2019, 10:26:22 AM
I bought both colours they came as a trial pack with four grades each down to very fine

The metal tubs itís in are about 40 mm dia 30 mm high

Itís a dry powder I mix with light machine oil as used on the lathe nuto32

Glad you found more info as posts are a chore when my dyslexia has a bad day ,Evan simple words look wrong and in a strange language it hard the describe how it looks , a good day itís fine

Stuart
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 27, 2019, 11:07:37 AM
Unfortunatley I can't find any reference to any suppliers of it in NZ. The top Google searches give me more links to Holland than NZ

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on August 30, 2019, 08:05:27 AM
A bit of an update

The two ignition units arrived from China on Wednesday. Hooray!!

(https://i.imgur.com/Gq2IPjm.jpg)

As they are from Aliexpress they needed to be tested and reciept confirmed. With AliPay the vendor doesn't get paid until you OK it but, once you've done it, that's acceptance.

So the first one out of the bag and connected up for a quick test.

23b5Zpl5_8Y
Then the second one out of its bag

(https://i.imgur.com/2OGlZns.jpg)

Only one HT lead. Damn!!

Check the bags again. Yes both RCexl 1222 twin 1/4x32 units.

(https://i.imgur.com/vok6ap4.jpg)

So now its onto the Aliexpress disputes process. So far the vendor is making the right responses. I buy a lot of stuff from China and on balance have had a good experience and if there have been problems they have been satisfactorily resolved. However, I have recently had one major issue with a vendor selling through Ebay that took three months to resolve. A case of once bitten twice shy.

In the meantime, I have started on the flywheel and inlet manifold. No pics of the flywheel yet

(https://i.imgur.com/haNloz0.jpg)

There is a bit of a saga with this but I'll save that until I've got the job completed.

Pete


Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 02, 2019, 10:20:06 AM
Iíve now got most of it done and trial assembled ready for a bit of fettling.

(https://i.imgur.com/FvWevoE.jpg)

(https://i.imgur.com/Ex1BEOv.jpg)

(https://i.imgur.com/lceA1B8.jpg)

I set the valves tonight and will do the ignition timing tomorrow. As itís club night on Wednesday Iíll just be tidying up a few other odds and ends rather than trying to run it as things start to get a bit messy once oil and fuel are involved. Anyway, I donít have the second ignition unit yet. The AliExpress vendor has given me a tracking number for the replacement so hopefully it will be in the system and on its way soon.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on September 02, 2019, 01:19:01 PM
Lovely job on those copper intake runners.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 02, 2019, 10:44:30 PM
Lovely job on those copper intake runners.---Brian

Thanks Brian

A bit of a saga with the manifolds. I was going to do them all in stainless, I had plenty of seamed ľĒ tube and a shortish length of seamless. The seamed tube doesnít bend very well and certainly not tight bends. With our dairy and wine industries one thing we donít have a shortage of is stainless steel but the minimum I could purchase was 6metres for NZ$150. Malcolmís write up for the Bobcat suggests copper so I decided to try that.

I made sure I had the dimensions correct for the jig plate for soldering. I did it in CAD and then checked the job. Drilled the plate and youíll see it all ready to go in my previous photo. Soldered it up and then came in for dinner. After dinner, the job had cooled down, I took it off the jig and checked it against the engine. Too short by 7mm!! Iíd used the dimension for the inner set of holes between the and inner and outer row. I am getting error prone these days and its beginning to bother me. Anyway, it all had to come apart and be done again, fortunately I managed to recover the central manifold.

As for the exhaust the short length of seamless tube was sufficient so I didnít need to purchase any more. Youíll notice that I havenít done the double bends as in my original CAD design as the pipework would have ended up too close the carburettor to be comfortable. If you are careful the 1/4" seamless stainless tube can be bent with one of these

(https://www.tooled-up.com/artwork/prodzoom/REC210.jpg?w=500&h=500&404=default)


Pete

Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on September 02, 2019, 10:58:22 PM
I am always tempted to buy some Cerobond. It is a solid metal at room temperature, but liquefies at about 180 degrees. Supposed to be the cat's meow for bending small diameter tubing without kinking. You heat it up with boiling water until it turns to liquid, pour it into the tubes, wait for it to cool off and solidify, bend your tubes, then heat the tubes up in boiling water to pour the Cerobond out. It's like a lot of things---I've heard about it but never actually used it.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 03, 2019, 08:02:16 AM
I've used pipe bending springs for 12mm/0.5" upwards, when doing plumbing. I recently obtained some small dia tube springs at a club auction but they don't go up to 0.25" although 0.25" springs are available.

Cerobond I guess is Woods Alloy. I imagine that it would make the bending a bit harder so you still need a suitably sized bending tool

The other trick, with larger diameters, is sand.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on September 03, 2019, 10:06:28 PM
I've been hearing that "fill your tubes with sand" song for 73 years. It never worked for me. I think that is an urban myth.
Title: Re: 30cc Flat Four (Puma)
Post by: Admiral_dk on September 03, 2019, 10:59:58 PM
Quote
I've been hearing that "fill your tubes with sand" song for 73 years. It never worked for me. I think that is an urban myth.

I have seen my dad do it in my childhood and he was an office worker, but to be honest, I do not remember how good the result was other than it was useable .... I'm on shaky ground here, but ... copper tube ...? :thinking: - I do also remember that he spend quite some time to stamp (compact) the sand and the temporary end-caps into place ....
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 04, 2019, 01:56:08 AM
I've been hearing that "fill your tubes with sand" song for 73 years. It never worked for me. I think that is an urban myth.

I must admit it probably didn't work for me when I was re-plumbing my house years ago so purchased a set of springs.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Art K on September 04, 2019, 03:39:34 AM
Pete,
I just thought I'd throw this out there. When I made my Upshur single I modified the valve guide so compression pressure couldn't push it out. That made it shorter and harder to center in the bore. I used a sharpie to see if the guide was in line with the valve. Put the marker on the head at the valve face, spin the valve in the guide, you can at least tell, the shiny spot is where the valve is in contact with the head, the broader the more the valve is in contact. In my case I had to tap the guide into position, I doubt yours is so complicated. A quick and easy way to see how much of the valve is seating.
Art
Title: Re: 30cc Flat Four (Puma)
Post by: Admiral_dk on September 04, 2019, 11:21:40 AM
I should have made clear, that I'm not sure my fathers result would have been considered a success for our use here - sorry ....  :-[
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 04, 2019, 09:12:45 PM

Pete,
I just thought I'd throw this out there. When I made my Upshur single I modified the valve guide so compression pressure couldn't push it out. That made it shorter and harder to center in the bore. I used a sharpie to see if the guide was in line with the valve. Put the marker on the head at the valve face, spin the valve in the guide, you can at least tell, the shiny spot is where the valve is in contact with the head, the broader the more the valve is in contact. In my case I had to tap the guide into position, I doubt yours is so complicated. A quick and easy way to see how much of the valve is seating.
Art


Art

This engine has combined guides and seats that are pressed into the head. The only real risk is distortion of the seat as a result of the pressing. The idea is good though and I do have some bearing blue that would be ideal for a similar test.


I should have made clear, that I'm not sure my fathers result would have been considered a success for our use here - sorry ....  :-[


The geat thing about these forums is the opportuinity to provide suggestions and alternative approaches and it is then up to the reader to determine which is most appropriate for their purposes. In a way there are no bad suggestions, although they should be limited to things that are not at all dangerous.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 09, 2019, 10:43:56 AM
Not a lot to offer by way of an update. The engine is all assembled and waiting for the replacement ignition unit to arrive. The tracking from China says it is on its way so we will see.

Quote


     2019-09-05 04:08 China, Shenzhen, Departure from country of origin. Your item is in transit to New Zealand



Although it's not a torpedo motor Jo has the opportunity to say "I told you so". When I was assembling it I used thread locker on the big end caps. It took some of the paint off so I had to strip it down again and remove the paint completely.

(https://i.imgur.com/ZjYrrUh.jpg)

A lesson learned. The paint may have looked nice but had no real purpose.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on September 09, 2019, 09:53:43 PM
I have only painted one of my thirty one engine models, and that was to make it resemble an engine I seen on the internet. The best and safest bet is no paint at all.  I do like the look of nicely painted engines, but I don't paint mine for the same reason you have found.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: bpudney on September 10, 2019, 04:51:10 AM
For what it's worth I have seen pipes being filled with sand prior to being bent on an industrial scale.   They even had a mezzanine to enable the pipe to be stood up vertically for filling.  It was a routine procedure for anything over about 75mm bore, in copper, copper/nickel/iron, steel.  The largest pipe I saw was about 500mm diameter, 6 or 7 metres long....it took a lot of sand!! For bending the pipe was dogged down on a big cast iron floor plate and heated with two huge gas torches.  Just heating the pipe up took several hours.  The person responsible was a early 20s guy only out of his apprenticeship by a year or two.  There were two big windlass' hooked up to the pipe by chain.  The "Master" was like a conductor, he directed the heated, told the people on the windlass' when to do anything.  When the pipe was being bent he was leaping all over it, tapping here and there with a 14lb sledge, keeping any ripples, creases etc at bay.

Anyway, there you are filling pipes with sand prior to bending definitely is not a myth.  All this happened in a shipyard in the UK, in the 70s.
cheers
Bill
Title: Re: 30cc Flat Four (Puma)
Post by: tghs on September 10, 2019, 11:36:19 AM
the larger the tube the better compacted sand will work, particle size and compaction,, scaling down the sand for smaller tubes could help,, in the mid 80's scale model ship combat started,, air powered guns aboard ships blasting BB's into each other,, to build the gun barrel systems small SS tubing with an ID of a BB (.177) needed tight 90 degree bends .. these bends had to allow the ball to pass smoothly.. cerrobend or woods metal  was used with a great success..I've used to make tight bends in small tubes.. pre-anealing the tubes depending on material.. the neat thing is for the most part it's a never ending product as once melted out of the bent tube with boiling water it will solidify to use again..
Title: Re: 30cc Flat Four (Puma)
Post by: Laurentic on September 10, 2019, 08:13:56 PM
Like Bill and for what it is worth, I also saw a copper pipe being filled with sand and bent under heat in a London ship repair yard in the 1960's.  I spent a few weeks in the blacksmiths shop and they had a maybe 6" diameter pipe to bend to fit on some ship and that's how they did it - filled it with sand, compacted all the way during filling and then stoppered top and bottom, and heated and bent.  Never forgot that.

They also re-white-metalled a big bearing - to suit a pin about 3-4 feet across.  When they set it up in the lathe and turned it down to size they collected all the white metal turnings and then melted it down and made white metal hammers for all.  I still have mine, a bit battered now but over 50 years old!

Chris
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 17, 2019, 09:34:02 AM
A bit of an up-date:

The 1200 grit silicon carbide 'tumbler powder' arrived the other day. I had been told it may be a bit fine as others had suggested 600 grit or 1000 grit. The 1200 grit did look a bit fine, finer than talcum powder, but I decided to give it a go.

Mixed with a bit of oil the paste seemed finer than Autosol but it did the job. With the valves, springs and caps in place and the ends of the valve stems held in a pin vice each head took about 5mins. Testing on the test jig they held 60 psi without any problem. When re-installed on the engine there is a noticeable 'notch' as each cylinder goes into and out of the compression stroke.

All I need now is the second ignition unit which apparently in in NZ and heading my way.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 19, 2019, 02:24:57 AM
Good news!

The relacement ignition unit arrived today. Sky-Fly Hobby Store, on AliExpress, were good to their word and replaced the single unit they'd sent in error with the twin I'd ordered. They didn't require me to return the single unit as it would have cost them more than their wholesale price.

Hobbying are still out of stock of their Phoenix clones of the RCexl units, I guess there may be a bit of a story behind that, so if you are looking for a supplier you could try these guys

https://www.aliexpress.com/store/group/Ignition/2622044_512156680.html (https://www.aliexpress.com/store/group/Ignition/2622044_512156680.html)

So next step is get the timing set up and see if I can get it to run.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 21, 2019, 02:33:54 AM
Well we have a runner!!

It was pretty painless, if you take operator error out of the equation.

The first issue was quickly apparent. Air was being forced into the fuel tank rather than fuel being drawn from it. Iíd set one of the camshafts on the wrong face of the lobe so the timing was out. It was sorted without a major disassembly. With the magnet disk removed and the grub-screw on the sprocket loosened the shaft can be adjusted. I used a small drill chuck to grip the end of the camshaft.

Next was the setting of the timing of the magnet disks. The RCexl tacho (the thing that falls off the bench about 1 min into the video) triggers as the magnet comes near the Hall sensor. I was using that as my indication of the trigger point. There is no indication in the RCexel documentation what edge is used by the unit. I was also concerned when the spark seemed to be intermittent. I now know that the unit requires both edges of the pulse from the Hall sensor to be seen before it will spark. The stable state is a high level, it goes low on the leading edge of the magnet and then high again on the trailing edge. Thatís when the spark is generated. These edges need to be in relative quick succession, which may be a reason why these units donít work that well for slow speed engines.

The carburettor Iím using is an ASP clone of the OS engines carb for their OS180FSR engine. I found the OS and ASP setup manuals and used the instructions to preset the carb. This video is directly after me doing that initial setup.

WM5IEEMxxNc
All in all Iím pretty pleased with the result at this point. As Jason reported with his flat twin, a bit of oil is being burnt by cylinders 1 and 3 as oil is lifted by the rotating crank. At the moment I donít have any baffles.

Thatís it for this weekend, we have a beautiful weekend here in Wellington so neighbours are out enjoying the spring sunshine so any more runs can wait for a weekday.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 21, 2019, 07:04:03 AM
That's running well for the first attempts, oil is not too excessive just hope you don't have an oily residue down the side of your car!
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on September 21, 2019, 07:25:55 AM
 8) Well done Pete

Jo
Title: Re: 30cc Flat Four (Puma)
Post by: bruedney on September 21, 2019, 07:35:15 AM
Nice one Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 21, 2019, 07:56:56 AM
Jason, Jo, Bruce

Thanks.

Fortunately, any oil didn't get as far as the car, as I had only washed it this morning. I do have an oil leak out of the crankcase but haven't discovered yet where that came from.

I've tweaked the cam settings a bit, my eyeballing of the exhaust valve opening wasn't as accurate as it could have been so I've re-done it with the DTI. I've also discovered why it shut down when I closed the throttle. The slow running stop wasn't set so the barrel closed off completely.

It looks like tomorrow will be another fine day. That said, it isn't as loud as I expected so may just give a brief run and get some close-up video, particularly of the timing belt in operation.

Pete

Title: Re: 30cc Flat Four (Puma)
Post by: Roger B on September 21, 2019, 08:30:08 AM
Excellent for the first run  :praise2:  :praise2:  :wine1:
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 21, 2019, 09:05:10 AM
Thanks Roger

I'm as surprised as anybody how well it went for a first try. The Bobcat and Lynx took weeks to get to run and even then they weren't that good. I'm learning a lot from this project, particularly what to expect. I'm already thinking that the Bobcat and Lynx will need to be dusted off and given another chance.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 21, 2019, 10:15:46 AM
So Whats Next?

Malcom did not get far but you could do the NE30-I4 or NE45-V6, it's really just the crankcases that change and he also went with Schillings style built up crankshafts..
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 21, 2019, 11:12:46 AM
Jason

The thought of making six of everything doesn't appeal that much. We did discuss whether this project should be a V4 or flat 4 and went for the flat 4.  Although it does cross my mind that, if I donated the parts from the Bobcat and Puma, I already have six of everything. With range of crankcases, cranks and camshafts the builder could assemble whatever took their fancy. A bit like Lego. Singles, Twins, 4 or 6 cylinder, inline, flat or V or even radial. RCexl do an ignition for 3, 5 or 7-cylinder radials.

BTW - I do like the way Malcolm reduced the spacing of the cylinders on the inline 6 I could have done that with the Puma, saved a bit of length on the crankshaft and reduced the 6mm shoulders on the journals.

Pete

Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 21, 2019, 01:07:07 PM
I think a one piece head would also go well with the straight 4
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on September 21, 2019, 02:30:20 PM
Congratulations. A very pretty little engine and definitely a runner.---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: Dave Otto on September 21, 2019, 03:55:55 PM
Nice work, congrats on the first pops!

Dave
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 21, 2019, 11:52:44 PM
Jason

A one piece head could look good but would move away from the concept of a modular design for many configurations

Brian

I'm pleased and it certainly appears to demonstrate the benefit of O rings vs CI rings which I picked up from one of your videos. In my case I've made the piston grooves to take CI rings but used 2 x 1mm section Viton O rings instead.

Dave

Thanks for your support

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Art K on September 22, 2019, 03:53:30 AM
Pete,
Sounds great for a first run, congratulations. DTI Is how I set the timing on my VAL. The indicators don't lie.
Art
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 22, 2019, 10:12:56 AM
Another video of a run today.

_SRKxsPd9BQ

At around 1 min 50secs a shot of the tacho, it shows just over 8000rpm. Lots of smoke from the exhaust which affects the smooth running. I know it is oil as it got all over the camera. So, it is time to think about the oil baffles.
 
Then at the very end a sudden stop and everything is locked up. An ďOh Bu88er!Ē moment and the thoughts of what I might find when I looked inside and lots of re-work

First thing was one of the rockers had moved on its bush

(https://i.imgur.com/0CoxstM.jpg)

Quickly fixed with a cleanup and Loctite

Draining the oil and taking the sump off there was a bit of gunk generated from the running.

(https://i.imgur.com/x851pQR.jpg)

Nothing major to be seen inside, and it now turned over freely. Then a tiny pin dropped out, it took a moment to think where it came from. Then realised it was one of the crank retaining pins.

(https://i.imgur.com/styELTI.jpg)

Again, easily fixed with a good clean out, primed with Loctite primer and secured with high strength Loctite.

I then time for the oil baffles for the sump. I decided to give my version a go.

(https://i.imgur.com/liojGqo.jpg)

If that doesnít work then Iíll try something like this.

(https://i.imgur.com/U99vasL.jpg)

Pete

Title: Re: 30cc Flat Four (Puma)
Post by: DavidLloyd on September 22, 2019, 10:35:51 PM
Congratulations on that engine Pete.

A good build log,

DavidLloyd,
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 23, 2019, 04:23:06 AM
Art, Dave

Thanks for your feedback.

I've not had time to try another run today, had other chores to deal with. The weather isn't looking too good for the next 2 days o i could be later in the week.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Johnmcc69 on September 24, 2019, 01:22:37 AM
 :ThumbsUp:
 Excellent work Pete! A beautiful runner!
Real nice design work on that.

 John
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 24, 2019, 08:00:07 AM
Thanks John

There is still work to be done to make it more reliable. I now know that with the sudden stop the timing went out and when I tried to start it today it wouldnít.

At first, I thought the worst and the wayward pin had jammed the camshaft and moved one of the cams. It turns out that I was correct about the camshaft jamming but what had shifted was the timing belt had jumped a tooth or two. I had been advised that it may be a problem as I didnít have enough Ďwrapí on the crankshaft sprocket

So now Iíve had another look and where in the past I had thought I could not use the next stock size belt (160mm) I now think I can fit it in. Iíve spent the afternoon on it and am having trouble getting the rear bearing mount out. So Iíve just shut up shop and come in for my dinner. When I go back out again, I will be in the frame of mind for a complete strip down rather that mess something up by trying to take a short cut.

More later in the week.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 24, 2019, 09:30:21 AM
It seemed to run OK with the shorter belt in normal running.

I'd personally prefer a belt to jump in a jam up than something get bent or broken
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on September 24, 2019, 09:45:14 AM

When I go back out again, I will be in the frame of mind for a complete strip down rather that mess something up by trying to take a short cut.

Pete

Hello Pete,

If you decide to do a complete strip down, would you be good enough to do a critical examination of the O ring piston rings and report back. It looks like they can handle the compression and power strokes but do little in the way of oil control and what about wear?

Your feedback would be very useful to others considering following the O ring route.

Playing with and developing small I/C engines is great fun and very gratifying. I have been quietly following along from the start.

Cheers

Mike

#OringvCI
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 24, 2019, 09:49:54 AM
It seemed to run OK with the shorter belt in normal running.

I'd personally prefer a belt to jump in a jam up than something get bent or broken

Jason

I found it easy to get it to slip, maybe the belt has stretched a bit with running. Iíve stopped for now to reflect on my options. Iíll take another look in the morning and see if I just need to work on the belt tension of go for the 160mm belt

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 24, 2019, 09:58:28 AM

Hello Pete,

If you decide to do a complete strip down, would you be good enough to do a critical examination of the O ring piston rings and report back. It looks like they can handle the compression and power strokes but do little in the way of oil control and what about wear?

Your feedback would be very useful to others considering following the O ring route.

Playing with and developing small I/C engines is great fun and very gratifying. I have been quietly following along from the start.

Cheers

Mike

Mike

I plan to remove the cylinders so will take the pistons out and get some photos. I purchased a second set of O rings so now it has run in a bit I may take the opportunity to replace them.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 25, 2019, 11:09:23 AM
Getting it all apart after it had been sealed up with gasket gunk was a mission. It took a bit of ingenuity and some cobbled together tooling to release things without making to much of a mess. Thereís not a lot to see apart from a pile off oily bits so no photos.

However, I did promise photos of the pistons.

(https://i.imgur.com/RHgYglw.jpg)

(https://i.imgur.com/erMLCpF.jpg)

I had expected more vertical marking on the pistons but there isnít anything major. The O rings look fine so Iím going to leave them as they are.

Iím going to go for the 160mm belt with more Ďwrapí on the crank pulley. Iíve made the mods to the tensioner. In the meantime, the crankcase is back in the paint shop as it came off worse in the disassembly.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on September 25, 2019, 02:20:27 PM
Hello Pete,

Thanks for the feedback about the O  ring piston rings. They certainly look to be an acceptable alternative to the normal iron compression rings, and a whole lot easier. It's not clear if they are so effective as oil control rings

Mike

#OringvCI
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 25, 2019, 10:31:39 PM
Hello Pete,

Thanks for the feedback about the O  ring piston rings. They certainly look to be an acceptable alternative to the normal iron compression rings, and a whole lot easier. It's not clear if they are so effective as oil control rings

Mike

Mike

I agree but I really don't have the experience to comment. Both my Lynx and Bobcat chuck out oil and they have CI rings. But with the Puma being a flat 4 it will tend to burn oil more than an upright engine so a direct comparison would be wrong. Jason has a similar experience with his Ocelot.

I used O rings because I saw that Brian used them succesfully. However, he uses a single larger O ring and it occurred to me last night that  hybrid may work O ring on the top CI ring at the bottom.

What it really needs is an experienced builder to do a comparison, 2xCI rings, Single large cross section O ring, 2 x O rings of same dimensions as the CI rings, 1x CI 1x O ring.

Then again its down to personal experience and preference. O rings have worked for me this time as this engine worked just about first go, but thats probably more to the approach I took to getting it to run. With the other two I was very green and had no idea which of the many variables I needed to address, so spent a lot of time tinkering with one thing after another hoping that it was the one. Although they ran they were never perfect, and the engines went on the shelf to look pretty. Once the Puma has got to its shelf time I plan to dust the others off and give them another go.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on September 26, 2019, 12:14:14 AM
Pete,

An oil control ring and it's groove is a completely different animal to a compression ring. To be effective, the oil control ring needs sharp vertical edges to scrape the excess oil film off the cylinder walls; the extra oil is returned via radial holes drilled though the piston skirt at the bottom of the oil control ring groove. Larger width oil control rings, can also have radial slits to double the number of edges available to scrape off the excess oil.

Oil control rings are usually fitted below the compression rings and occasionally in the piston skirt below the wrist pin.

Most of our model engines only have one or two compression rings and very few are designed to include a true oil control ring. Your Puma build shows that two O rings look to

#OringvCI
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on September 26, 2019, 01:29:54 AM
Viton o-rings do an incredible job of sealing a piston in a cylinder. Based on experience, I use a single 1/16" nominal cross section o-ring in a 0.094" wide slot x 0.058" deep in the piston. Would they serve as an oil control ring?--I think they would. The oil in the crankcase only gets thrown into the cylinders on one side. I built my twin cylinder opposed engine without a wet sump, because of experience that Jason had with oil control in a very similar engine. My engine has a lift off cover, held in place by magnets, that allow you to lift the cover and oil the con-rod big ends and small ends with an oil can. This avoids any oil control problems.  If I had the time and patience, I would remake the pistons on the "oily" side, and have one Viton ring at the top end, and one Viton ring close to the bottom end, with a series of 1 mm holes thru the piston skirt immediately below that Viton o-ring.  I've never done that, but I think it would work well for oil control. The only downside to using Viton rings is that they have a considerably higher drag coefficient in the cylinder than cast iron rings. This doesn't really matter in a throttled engine, but greatly affects the number of "coast" cycles that the engine will do before it hits again. They won't work in a two cycle engine that has ports in the cylinder wall either, as they will "bulge" into the ports and either stall the engine dead or be quickly eaten away by repeated passes over the port.
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 26, 2019, 07:19:07 AM
Biggest problem for most of us would be scaling down a proper oil control ring and suitable skirt thickness. With pistons of 20-25mm dia the skirt is usually around 1mm thick by the time you add on groove depth you will have a wall of maybe 2.5mm and then start to get problems with the conrod hitting the piston not helped by the fact most models have pistons that tend to be equal or longer than the diameter not short ones with cut away sides. Then there is the fun of drilling a 1mm x 1mm cross section iron ring and fitting it without damage! Also with many people adding a small amount of oil to their fuel you will get some of that coming out the exhaust.

Vitron Quad-rings would likely have more of a scraping action, I do have a casting kit that specifies one of these as the only ring and from what I have seen of them running they work well Though a bit of oil out the exhaust may not be a bad thing as we don't have enclosed rockers, guides, and oil in the top of the engine in a lot of cases.

I've only run o ring sin the slower IC engines with a single or below iron rings. Current Midget engine project will be higher revving and only O ring sealed so we shall see how that goes.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 26, 2019, 10:20:54 AM
I'm sure there are those out there capable of making miniature oil control rings, I'm sure I've seen it done with a V8/V12 build. Itís not something I'd attempt.

As these O rings fit the 1mm x 1mm groove for CI rings they are just 1mm cross section. They don't seem to drag that much the only minor problem is a degree of stiction from stationary. As you've seen, this engine has run up to 8000rpm, albeit briefly. Weíll see how we go with longer runs.

I like the idea of quad rings and plan to fit them to my loco once the existing Viton O rings have had their day. I had thought they would be difficult to source but went to my local supplier and they had them in stock. As simple as deciding on the normal O ring youíd want and add a ĎQí on the front of the number.

Update - Crank case is out of the paint shop and redied for re-assembly. I'm going to take it easy to see how I can get it together and sealed up enought to stop the external oil leaks but able to dissassemble for maintenance.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 26, 2019, 10:25:22 AM
May be worth tapping a couple of holes in the sump and end cover flanges so you can use a jacking screw to help get things apart, often seen on old steam engines
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on September 26, 2019, 11:13:42 AM
We are in danger of spoiling Doubletop's excellent Puma build with all this O ring piston ring discussion. Perhaps it would it be a good idea for Jo, or one of the other admins, create a new topic called "O rings as piston rings" or something similar. Then transfer the relevant replies #175 to #179 and this one, to the new topic.

Here are some thoughts about developing the O ring piston ring concept further.

An iron piston ring creates the initial wall seal by spring tension. The compression/ combustion  gas pressure then gets behind the ring and forces the ring tighter against the cylinder wall. The current thinking with O ring piston rings is to precompress, or nip,  the O ring by a few thou, by controlling the groove depth. This gives rise to higher static ring friction. Could an alternative approach be to use a slightly over-diameter O ring (say 26mm OD in a 25.4mm bore) provide the initial seal, with clearance on the ID. Gas pressure could get behind the O ring to increase the sealing force, in the same way as a conventional iron ring. Only a slight change in philosophy and dimensions, but it could have a beneficial effect.

The quad ring appears to have a number of advantages over the plain O ring both for both compression and oil control. The square section would appear to provide a better shape to scrape excess oil off the cylinder walls. The excess oil still needs to escape through the radial drain holes through the piston wall. These drain holes could be blocked if the O ring is precompressed, Perhaps an over-diameter ring with clearance on the ID would work better.

It would be very interesting to be able to make a direct comparison between an oversize O ring, with ID clearance, and a precompressed O ring, as a method of reducing ring friction.

My thoughts

Mike

#OringvCI

Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 26, 2019, 08:48:07 PM

May be worth tapping a couple of holes in the sump and end cover flanges so you can use a jacking screw to help get things apart, often seen on old steam engines


Jason

I had the same thought and made a start yesterday and included them on the end cover flanges however the cylinders would also benefit so I'll do them as well. I'm using a paper gasket on the sump as that doesn't interfere with overall dimensions.

Pete


We are in danger of spoiling Doubletop's excellent Puma build with all this O ring piston ring discussion. .........................


Mike

Not at all, as far as I'm concerned stimulating a discussion is one of the purposes of these forums. Thats how we learn, or at least that's how I learn. I've always said I did my ME apprenticeship on these forums.

Maybe we should adopt the social media habit of including #hashtags in our posts so a search for say #Orings or #OringvCI will bring up all the threads on the subject (a search will find this one now  ;D ). I'm sure there will be a number of discussions that would benefit from retrospective #hashtagging. The mods could add a sticky on the topic #Hashtags and maintain a list of those to use so everything gets correctly grouped.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 26, 2019, 09:07:26 PM
Viton o-rings do an incredible job of sealing a piston in a cylinder. Based on experience, I use a single 1/16" nominal cross section o-ring in a 0.094" wide slot x 0.058" deep in the piston


Continuing the Oring discussion I see from Brians dimensions that he is using the Orings as designed. A gap wider than the O ring cross section (50%) so the pressure can get behind it and deform the ring against the walls and a 7.2% squeeze. Also using only one ring, a second ring won't do anything as if the ring on the pressure side is doing its job the secod ring won't get any pressure to deform.

In my case I'm not following the rules. Two rings and a gap but not 50% and squeeze that is probably not more than 4%. With a 1mm ring thats only 0.04mm or 0.0015"

P.S; I've just asked my supplier and the smallest cross section for a quad Oring is 1.8mm. I won't be modifying my pistons to be able to use them and making 4 more pistons isn't on the cards at the moment.

#OringvCI  ;D

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on September 26, 2019, 11:17:10 PM
Maybe we should adopt the social media habit of including #hashtags in our posts so a search for say #Orings or #OringvCI will bring up all the threads on the subject (a search will find this one now  ;D ). I'm sure there will be a number of discussions that would benefit from retrospective #hashtagging. The mods could add a sticky on the topic #Hashtags and maintain a list of those to use so everything gets correctly grouped.


Pete

The hashtag idea may or may not catch on with the MEM membership, only time will tell.

I have gone back and retrospectively added the #OringvCI hashtag to all my related posts, I cannot do that to everyone else's posts. At least I will be now be able to refer back to these posts, at a later date.

Mike
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 27, 2019, 07:15:06 AM
#Orings, #O-rings, #O rings

That should cover all eventualities ;)

I also use the usual slightly wider and lightly shallower groove sizes. Not the ones you will find published on most O ring suppliers sites but the ones in Model Engineers Handbook and Reeves paper catalogue which do not compress the ring as much so there is less friction.

For an actual 2.4 C/S ring that would be 2.6mm wide x 2.3mm deep. Also along the likes of Mike's thoughts that is a 19.6mm ID x 24.4mm OD ring in a 24mm bore and bottom of groove is 19.4mm dia
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 27, 2019, 10:25:28 AM
The way the search engine works there only really needs to be one hashtag in the thread as the basic search just gives the most recent post that meets the search criteria.  So if a thread goes off in an interesting direction a single hashtag near the start which will get people to the beginning of the discussion.

Iíve started the re-assembly. The cylinders still complete with their valves and pistons, with my finger over the spark plug hole it is impossible to push the piston into the cylinder by hand. That tells me the O rings are working well, whether to recommendations or not

A bit back to front but as Iíve modified the timing to use a 160mm belt Iíve updated the drawings

(https://i.imgur.com/fTxwppN.jpg)

As I said -re-assembly has started

(https://i.imgur.com/zQVNHvS.jpg)

The 160mm belt and tensioner. Now with 6 teeth of the crank pulley engaged rather than the previous 3 or 4. You can also see the tapped holes for the jacking screws to hopefully enable an easier disassembly.

And with the timing sensor loosely fitted.

(https://i.imgur.com/nTRo59e.jpg)


Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 28, 2019, 08:58:16 AM
Iíve got it all back together and gave it a quick run this afternoon.

0cAAbN5lN18
I did fill it with oil and the oil baffles seem to be working. Only an occasional quick puff. I was trying to see how slowly I could get it to run.  I had to keep holding on he the throttle as the vibration keeps opening it up and the revs rise. It did run slowly and was remarkably quiet with the occasional loud crack and there was also an element of hunting. Iím assuming the cracks are a timing issue.

When I set it up this time the right-hand cam, cylinders 2 and 4, seemed to be out slightly. Setting the camshaft on exhaust valve #4 opening exhaust valve #2 was about 10degress late. I compromised and set it between the two. The left-hand camshaft was spot on. I canít remember if that was a problem the first time I set it up or just overlooked checking it. I had been very careful when I assembled the camshafts so there shouldnít be a problem. However, the only way to find out is strip it all down again. The only way to get the camshafts out is a complete strip down as the bearings are fixed in place.

Regardless of the possible camshaft problem I was happy with the way the oil baffle worked.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 28, 2019, 10:09:38 AM
That exhaust looks a lot cleaner now with the baffles in place
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 28, 2019, 11:52:14 AM

That exhaust looks a lot cleaner now with the baffles in place


And there's no oil leaking out of the crankcase. Did I remember to put some in?........ ;D ;D

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: AlexS on September 28, 2019, 08:25:51 PM
Great engine and build log!! What about a dyno run?
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 28, 2019, 10:55:36 PM

Great engine and build log!! What about a dyno run?


Thanks Alex

Dyno run? I understand the theory but what is the method generally used for model engines?

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Brian Rupnow on September 28, 2019, 11:04:33 PM
Doubletop--Look up "Prony brake". That is a method used to calculate engine horsepower. There are Youtube videos of it being applied to model engines. ---Brian
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 29, 2019, 02:43:10 AM
Doubletop--Look up "Prony brake". That is a method used to calculate engine horsepower. There are Youtube videos of it being applied to model engines. ---Brian

Brian

Of course and would be easy to set up against the existing flywheel with webbing strap and a $10 digital baggage scale.

It could be on the 'to do' list once I've got the engine running a little better.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on September 29, 2019, 07:16:28 AM
The other method is to put a full length prop on it and measure what revs it will do, there is then a formula that will give the HP.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 29, 2019, 08:02:16 AM

The other method is to put a full length prop on it and measure what revs it will do, there is then a formula that will give the HP.


https://www.rcgroups.com/forums/showthread.php?1077012-Measuring-motor-power-output (https://www.rcgroups.com/forums/showthread.php?1077012-Measuring-motor-power-output)

Apparently no prop is required, just a stick. Although I would be a bit wary of a 6mm x 26mm plywood 'stick' spinning at 8000 rpm, I'd have visions of it parting company with the engine and launching itself at the neighbours place. However, the material used is apparently irrelavant as mass has no part to play in the calculations.


Pete
Title: Re: 30cc Flat Four (Puma)
Post by: tangler on September 29, 2019, 11:48:14 AM
There's a formula (of uncertain provenance) that gives Horse Power figures that are comparable to some engine tests that Peter Chinn used to publish.

BHP = 7.105 x 10-18 x D4 x P x R3

Where D is prop diameter, P is the Pitch (both in inches) and R is RPM

HTH,

Rod
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on September 30, 2019, 01:38:49 AM
Rod

Thanks for the input, weíve started something hereÖ

I went looking for references to Peter Chinn to support the formula provided by your input. It turns out that Peter Chinn used his own set of calibrated props to get results. And if you read the articles in the links below all props are not equal. In Peter Chinnís time even the same prop from the same manufacturer wasnít equal

http://www.adriansmodelaeroengines.com/catalog/main.php?cat_id=57 (http://www.adriansmodelaeroengines.com/catalog/main.php?cat_id=57)

http://www.modelenginenews.org/techniques/testing.html (http://www.modelenginenews.org/techniques/testing.html)

Where does this take me? Back to letís get the engine running properly and maybe then Iíll try a Prony brake.

Pete

#Dynamometers


Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on October 01, 2019, 06:32:09 AM
I gave it another run and although there was an improvement over previous runs it was clear it still needed some work. One benefit of a multi cylinder engine is that if one cylinder isnít working as well as the others it is pretty obvious.

Iíd previously noted that one of the cams on one of camshafts were not correctly aligned, I was also aware that two of the cylinders had considerably more compression than the other two.

So time to strip it all down again and this time get the camshafts out. The jacking screws certainly helped to make the strip down a lot easier.

(https://i.imgur.com/ApGdnhZ.jpg)

Youíll notice the cam shaft has been disassembled and the crank is missing. With it all apart this time the problem with one of the crank pins coming out was obvious, one of the joints on the centre web had failed. So that was the first thing to get fixed.

I checked the angular location of the cams and confirmed they were out. The right hand (2,4) camshaft the two exhaust cams should have been 90deg apart they werenít. Same for the inlet cams on the left hand side (1,3)

When Malcolm wrote up the Bobcat article, he proposed a simple jig to align the cams

(https://i.imgur.com/br8W9GW.jpg)

Youíll notice that even in this photo it is possible to get the cam incorrectly located in the V of the jig. Any error on the camshaft alignment is doubled at the crankshaft.

I re-made my jig to better fit the shape of the cam to better ensure correct alignment.

(https://i.imgur.com/thqmaYe.jpg)

Investigating the two cylinders with lower compression was an easy change of the O rings. I guess they wore more quickly doing the run in.

Loctite is now curing and Iím cleaing up the other parts. Then its back together again

Pete


Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on November 18, 2019, 12:25:46 AM
Time to get back to this. After the camshafts were set I re-assembled and had had a brief attempt at running it. It wouldn't run so it got parked.

Next was a flight from NZ to the UK for a holiday which included a visit the Midlands Show. Where I manged to miss Jason and Stewart Hart by feet, not even days, hours or minutes. We were all in the cafeteria at 11:30 on the Thursday. While I was in transit the arrangements had been made to meet at the 'green X' and I missed the thread. However, I was in the same cafeteria at the same time but being unaware of the arrangement wasn't looking out for them. Maybe another time. I did manage to catch up with Roger Froud and Rex Hanman and a couple of others who, I'm sorry, I didn't catch their names.

I've been back two weeks now and got some other jobs out of the way so back to the engine. I'm currently re-setting the timing then I'll see if it runs. I just hope that I didn't stuff up the re-assembly of the camshafts....

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on November 18, 2019, 11:04:09 PM
The problem with starting was pretty soon sorted. I'd set the camshafts for 1&4 and 2&3 operation and the firing as 1,4,3,2 that clearly wasn't going to work.

Getting the cams more accurately located on their shafts and using a DTI to set the lift point certainly paid off.

On this run Iím using an RC servo to set the throttle so I have better control while I tweek the carb. It's a pity the rev counter isnít in view. But Iím getting around 1500 to 8500rpm

b-MQ1PyI5T4
I did a few more starts after this and then the engine would not restart. This time the timing belt sprocket has moved on the camshaft. Clearly one 6ba grub screw is not sufficient. Iíll make provision to 2 or more. Filling flats wonít work as it would just about be impossible to get them correctly located and maintain the correct cam settings.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jo on November 19, 2019, 08:33:26 AM
 8) Nice one Pete.

Jo
Title: Re: 30cc Flat Four (Puma)
Post by: Admiral_dk on November 19, 2019, 11:50:58 AM
Quote
Clearly one 6ba grub screw is not sufficient.

I can't say that this surprises me with the engine size you are doing ....
You need a total fixed mechanism (I will not exclude Locktite), like a pin or better a key.
Why - well, any kind of possible angular movement, WILL end up destroying the "fix to axle" - simply because the opening and closing slopes off the cam, will create opposite twisting forces.
I'll bet that the grubscrew created a "furrow" in the axle, from the back- and for-ward forces.

The engine runs very nicely at the start of the video + looks great :ThumbsUp:

Best wishes

Per
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on November 19, 2019, 07:20:40 PM
Thanks Jo

Quote
Clearly one 6ba grub screw is not sufficient.

I can't say that this surprises me with the engine size you are doing ......


Best wishes

Per

Per

It is a result of creating an engine based on another design. With Malcolms orginal design with a single camshaft and using a geared drive there is an opportunity to get the camshaft set up, use the grub screw  to create a witness mark, take it all apart, machine a flat at the right location and get it all back together in alignment. Malcolm says 'file a small flat... it is easy to adjust this flat to ensure the gear is in the correct position'.

With this engine it is not so easy using a belt drive and filing flats and reassembling two camshafts at the correct angular relationship to the crank could be troublesome. That said writing this reply has made me stop and think and I have some ideas to try.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Admiral_dk on November 19, 2019, 08:42:06 PM
Quote
That said writing this reply has made me stop and think and I have some ideas to try.

I have experienced this many times - either with me explaining or the other person doing this - and it often happens to reveal a useable solution when one has to explain the problem in such a fashion that the other person understand what you're facing .... often before having finished the "lecture" about the problem too  ;)

Per
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on November 19, 2019, 09:05:38 PM
Quote
That said writing this reply has made me stop and think and I have some ideas to try.

I have experienced this many times - either with me explaining or the other person doing this - and it often happens to reveal a useable solution when one has to explain the problem in such a fashion that the other person understand what you're facing .... often before having finished the "lecture" about the problem too  ;)

Per

That's the benefit of these forums. The interaction makes you stop and think rather than plough on regardless.

I would tell junior project managers to write their weekly status report regardless of whether they thought anybody would read it. The action of stopping and taking stock refocuses from the reactive day to day problem solving back to the big picture.


Pete
Title: Re: 30cc Flat Four (Puma)
Post by: scc on November 19, 2019, 09:39:12 PM
Nice engine Pete,       Terry
Title: Re: 30cc Flat Four (Puma)
Post by: Dave Otto on November 20, 2019, 01:07:57 AM
She runs and sounds great Pete, congrats!

Dave
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on November 20, 2019, 08:24:55 AM
Terry & Dave

Thanks guys. I'm pretty pleased with it, my 2 previous engines have never run as well as this. They are both up or some rework once I've sorted the minor issues with this one. I've learned a lot.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on November 23, 2019, 08:20:56 AM
I had a think about how I was going to create some registers on the camshafts for the timing pulley grub screws and still maintain the correct orientation. I had in mind some sort of jig that I could use to lock the camshaft and crankshaft orientation, move the pulley out of the way and create the flats at the witness marks left by the grub screws. Amongst other things major problem was the ends of the camshafts, that held the ignition magnets were just not long enough to accommodate the clamp and get they pulley out of the way.

I had already added a second grub screw at 90deg to the original so it occured to me I could remove one grub screw and insert a drill down the hole to put an indent on the shaft. Replace the grub screw and do the second.

(https://i.imgur.com/fNBjmLx.jpg)

The problem with that would have been the possibility of damaging the thread if I used a twist drill.

Iíve used 6ba grub screws for which the tapping drill size is 2.3mm I have some 2mm piano/music wire so decided to try a D bit. The advantages being that I could grind the end to the 90deg of the tip of the grub screw and there would be less chance of damaging the threads.

(https://i.imgur.com/qOtXSFz.jpg)

The brass collar is a stop set for a 1mm indent in the 4mm camshaft.

I had thought that piano wire is capable of being hardened and tempered like silver steel. It proved not to be the case. Case hardening with ďCherry RedĒ (Kasenit equivalent) did the job.

(https://i.imgur.com/22YE6AW.jpg)

The indents were done Ďin situí so the timing didnít get disturbed. The drill vice used to clamp the two shafts together and stop them moving. It was all very easy in the end

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Vixen on November 23, 2019, 10:40:40 AM
Hi Pete
It often happens that way. Your greatest fears can turn to nothing. Making an end cutter fromm piano wire is a brilliant idea. If you have room, try to fit a second grub screw on each hole to lock the one below. It works very well.

Mike
 
Title: Re: 30cc Flat Four (Puma)
Post by: Admiral_dk on November 23, 2019, 09:08:07 PM
I'm happy to hear that you found a useful solution and sorted the problem  :ThumbsUp:
Title: Re: 30cc Flat Four (Puma)
Post by: Art K on November 24, 2019, 03:17:10 AM
Pete,
That was a good run. I like the RC controls for the throttle, to me that seems like a novel solution to throttle control. I have no doubt you will sort out the remaining problems & have a steady dependable runner.
Art
Title: Re: 30cc Flat Four (Puma)
Post by: Roger B on November 24, 2019, 08:02:35 AM
That looks to be a good solution  :ThumbsUp:  :ThumbsUp: Fine camshaft timing is always difficult in these sizes. If you can find a way to fit a 60 tooth gear it all becomes much easier as one tooth is 6 degrees and two keyways offset by 3 degrees allows adjustment to 3 degrees. The camshaft sprocket on my old Triumph had two pairs of fixing holes offset from the teeth such that by turning the wheel around you could get 1/4 tooth resolution.
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on November 29, 2019, 09:10:51 AM
Art

The servo controlled throttle idea comes from a project I had going a few years ago where I had the ignition controlled by a PIC microcontroller using an in-plug coil unit for the HT. The idea was that the ignition parameters could be adjusted, real time, on a running engine. The micro controller was used to set the throttle  position and then the advance adjusted to the best running position and then the data saved. The advance curve could then be setup across the rev range. It sort of worked but the engine under test, my single cylinder Lynx, wasn't that reliable and I got bored. Now I better understand what I should have been doing I may resurect it.

Roger

Interesting that you say that because it crossed my mind as I recalled something similar from my car tinkering days. I could well have been a Triumph. I've a picture of it in my mind.

Pete
Title: Re: 30cc Flat Four (Puma)
Post by: Jasonb on December 22, 2021, 08:07:08 PM
Pete's Puma is now in Print  :)
Title: Re: 30cc Flat Four (Puma)
Post by: doubletop on December 28, 2021, 07:04:29 PM
Pete's Puma is now in Print  :)

We'll that is a nice surprise!! I was wondering when Martin was going to print the article as I sent him the draft a while ago. With the supply chain issues my copies of ME donít get to NZ until weeks, even months, after the publication date.

Iím looking forward to seeing it

Pete