Model Engine Maker
Engines => Your Own Design => Topic started by: Brian on January 05, 2016, 05:30:15 PM
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Hi all .
I have been working on this design for over a year now and started making chips about two months ago.
The design has been through so many revisions that hardly a thing is unchanged from the original pencil and paper doodle.
I hope you enjoy watching this engine come together over the next two to three years. If you see any thing you don't understand please feel free to comment as I may be wrong in the first place.
So first a general arrangement drawing. front view. I am afraid my drawing skills are not at all professional so for that I apologize.
Brian.
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Don't apologize for that drawing! It's very clear. This should be very interesting to follow and I look forward to this build.
Pete
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That looks an interesting engine :ThumbsUp: :ThumbsUp: How are you planning to drive the cams?
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Hi Roger
Cams are driven by timing belt behind the cylinders,
Brian.
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I have rummaged around in the old files and found a drawing of the belt and gear layout of the cam drive, Most of the engine is incorrect and no belt tensioner because I had not even decided on the direction of rotation at this time. However it shows the basic lay out.
Also a photo of things as they stand at the moment.
the heads are in different positions to show the main areas of work & one of the cylinders.
Brian
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While waiting for the bronze for the valve cages to arrive I have made a valve seat cutter from silver steel, turning the 1/2"bar down to 3mm was a bit of an adventure but we got there in the end.
Also acquired a inside micrometer to help get the size for the shrink fit right.
Brian.
http://www.modelenginemaker.com/Smileys/default/happy-132.gif
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Well the bronze arrived and Disaster came with it
I very carefully made two valve cages with a .003" interference fit thinking I could shrink fit them in to one of the heads,
despite getting the head really hot the set up grabbed when only half way, the use of force resulted in one seat being driven in two deep damaging the cage seat, and the cage broaching a sliver of metal from its bore, the other cage went in flush with the face of the combustion chamber but also broached its bore due to the force required to drive it in.
So having a dead head on my hands I reprofiled the chamber to meet the face of the sunken cage with a diamond burr the continued with cutting the inlet tract and valve throat and proving the seat cutter. the dead head will now be to set up further operations.
Now I have to review what I am going to do about installing the remaining cages, so It's time out for the moment on the heads
The material for the cams - valves and cam boxes has also arrived so I am not short of things to do On top of making a new head to replace the damaged one.
Searching The forum has produced a lot of information on how others have tackled this job but I am open to advice regarding your experiences . The intention is to eventually fly this motor in a model based on the Spirit of St Louis so it has to be reliable.
The attached photo of the damaged head shows the reprofiling nearest the camera.
Brian...H
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I question the need for valve cages. Bronze or CI valve guides are a good thing but with the number of hour use the engines we make are going to get valve seats directly in the aluminium head are probably ok. The risk to an engine of a cage coming loose seems far greater than having a leaking/burnt valve seat.
Just my 2 Rappen.
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Three thou is too much for a small part like that, even a shrink fit. I would think that one thou would be a heavy press fit
for that. A small hole like that in the middle of a big chunk of aluminum isn't going to expand much when heated either.
That's my gut feeling based on experience. My two cents if you will!
I hope you get this sorted out 'cause I really like your engine concept and the build so far.
Pete
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I question the need for valve cages. Bronze or CI valve guides are a good thing but with the number of hour use the engines we make are going to get valve seats directly in the aluminium head are probably ok. The risk to an engine of a cage coming loose seems far greater than having a leaking/burnt valve seat.
Yes, the hand-wringing pros & cons of this valve seat business. The downside that I (personally) fear more is buggering up that delicate little 0.015" valve seat in the head which also means its a binner, just by a different mode. After practicing 'more than a few times' on valve cages outside the head, my experience is that it took some technique. Pass/Fail was validated with a vacuum gage on the exact same test valve. Unfortunately, quite a few 'fails' until I got the hang of it. My logic is if the valve + cage seals outside the head & I don't manage to distort it fixing it in the head, that gives me a fighting chance. I was also concerned about the cage letting go under temperature cycles. But in my case there is quite a bit of surface contact area. I used a torch up to 450-ish a few times & it took hard whacks before it let go. So, this amateur is crossing his fingers...
FYI, link below of Terry's 18-cyl build. He sized the 544 bronze valve cage OD .0005" under the corresponding bore ID in the head. He used high temperature (450F) Locktite 620 retainer, added glue grooves around the body of the cage & gave it some 400 grit surface treatment.
http://www.homemodelenginemachinist.com/showthread.php?t=21601&highlight=valve+guide&page=15
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Is it my eyes, or is one of these combustion chambers an 'inny' & the other is an 'outy'? What am I looking at here?
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Thank you all for your input regarding this problem this is the first time I have made valve cages and obviously need advice .
I will be studying the link to Terry's radial later but first I think a run through of the how and why of this build may be in order.
The majority of the parts on this engine are built on two jig's One for the cylinders and heads & the other for the casing.
Looking at the photograph showing two views of the head , the one on the right is the combustion chamber, the other shows the top view with the cam followers and the large spigot that fits into the jig, this will not be removed untill the very last.
Because the overhead cam decides the orientation of the valves & and in turn the spark plug position Number 4 cylinder has it's plug on the opposite side to keep it away from the oil draining down when the engine stops.
The crank case and its associated sections --nose --inner bulkhead--gear case --belt case and back plate all share the same size
location flange this will allow me to change components on the casing jig without altering settings and even stack sections on the jig to ensure alignment is kept.
These jigs accurately fit both the rotary table and the lathe so set up time is minimal.
The overhead cam allows me to individually set valve and ignition timing for each cylinder eliminating the compromises that
are normally made due to the master rod layout.
The fuel for this engine will be Propane.
After all this if you feel like asking why, My answer is ,Why Not.
This is the section through number one cylinder showing the general layout of components, but like all others is constantly under review,
Brian.
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Brian:
Looks like a lot of design time in this. And I agree, for a model engine "why not" is an excellent reason. It should be a fun build to follow.
I second Pete's thinking that 0.003" is a very heavy press. Without looking at a reference, I'd think something under 0.001" would be better.
Thanks for taking us along.
Hugh
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Thank you Hugh for your input.
These are the jig's that fit the lathe and R T the 3 MT fits the lathe and the 2 MT fits the R T each has a spigot that fits both jigs
and has a thread so work on the jig can be fixed independently of the studs if required
The case jig has an adaptor ring to convert it from male to female location when the need comes to flip over the part. special Tee nuts on the R T ensure that 0° lines up spot on.
The face plate was incorporated into the lathe set up just in case a different method of location is required at a later date.
Brian.
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Thanks for all the help lad's I think I have it sorted now.
Reading Terrys Radial took me half a day but was worth every minute. What a mine of information. Thank you Terry.
I will now push on with the replacement head Just as soon as I get over the stiffness from falling down the stairs.
Brian H
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Hi all
if you want to catch up on this thread you may like to look at https://www.youtube.com/watch?v=5BAUrD6AsII this is the first of three
slide shows with a little video added.
Sorry I am not very good at downloading or making video yet I hope to improve but it is another call on my poor 75 year old brain.
Brian H
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Great slide show Brian.
I hope to see the other two.
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Ok Carl No 2 coming up
Brian. H
https://www.youtube.com/watch?v=KsJvTsjiQIc
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I cant seem to get them all on one post so here is No 3
Brian H
https://www.youtube.com/watch?v=smCKkDWyY-A
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Thanks for taking the time and trouble.
I enjoyed! :ThumbsUp:
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At last i have good results . thanks to all the help.
the cages are in and look good so far when I have the valves made I will built a test set to prove the sealing.
I have done another Video it's not good I lost the captions in the download You can see it on my channel ( brian hogger) but I will try to load it here.
https://www.youtube.com/watch?v=dTrIgprpNIQ To see if it works.
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I think I have it now
https://www.youtube.com/watch?v=dTr1GPrpN1Q
Keep fingers crossed.
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The next part is the cam box a small piece of aluminium with lots of holes just trying to get them to miss each other is a major achievement. lots of holes and no room.
Brian H
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Looks good Brian. :ThumbsUp:
I'm looking forward to see more. :cheers:
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Looking good! Looking forward to seeing more
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A quick update on progress.
The camshaft has been cut and fitted in the cam box with Oilite bearings,
I am waiting for the screws and tap to arrive so I can assemble the head, then the next step is to
cut the valves to length and set the valve clearances.
When I am happy that it all works correctly the edges at the front of the box formed to match the curve of the head.
Brian
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Ok off we go again. the next job was to establish the length of the valves and then drill the hole for the pin.
the valve lash is minimal the followers just clear the base circle, the thinking is that the head is likely to expand more than the valve so clearances will increase when the engine is hot.
The head was then given a test run on the lathe, all seems OK the followers are revolving in the guides to spread out the oil film and reduce wear so I am a happy bunny.
Brian.http://www.modelenginemaker.com/Smileys/default/happy-132.gif
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Looking good :ThumbsUp: :ThumbsUp: Four more to go ;)
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Further work done to tidy up the appearance and fit the timing gear that turned out to be not as ordered so I await a reply from the company.
Brian.