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Re: Cylinder Hone for overhaul
My goodness Its a wonder our engines run at all after being honed so the rings will seat. I informed an old NASCAR mechanic if we should use a torque plate on our engines, he laughed and said "absolutely Not, forget about a torque plate. You ase not torqing down crankshaft main bearing caps that could distort the block". More non related stuff on this subject.
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Re: Cylinder Hone for overhaul
Sorry about the previous post I asked an informed ols NASCAR mechanic the question
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Re: Cylinder Hone for overhaul
Many years back - Wankel released a license for small engines and In Germany a small model aircraft engine wa made
It was a turkey The license was bought by OS in Japan and their engineer reworked the design -getting toleraces such that when the engine warmed up - the tolerances were correct for best power. this change, roughly doubled the power output. I made a twin using two of these ,driving a Gilmer type belt at 2-1. I ran th engines at a crank output speed of 18000--20000 rpm the result ws very smooth but the drive hubs were not correct and I got edge wear on th e belts also th e setup burned fuel at a fierce rate - the VE of the setup was NOT good. fun experiment tho--and the plane worked very well -a CAP 21 I designed. 920 squares 9 lbs all up. |
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California
Joined Jul 2006
4,329 Posts
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Re: Cylinder Hone for overhaul
For the sake of clarity we're referencing model engine here, not NASCAR, motorcycle, or other higher end engines. So we might want to bring this back to items that can actually apply to what we use for flying.
Following a sound bolt tightening procedure, with the final tightening sequences performed with a torque wrench, will provide the most true cylinder base of any of the usual methods used. Most will simply tighten the cylinder screws down with, at best, a T handle hex key. The next brightest people will tighten the base screws in a cross pattern. The next better educated ones will use a cross tightening pattern, doing each a little at a time until tight. The real bright ones will use a cross tightening pattern a little at a time, finalizing with an accurate torque wrench and working the finals a little at a time. Think it won't make a difference? On our little engines it can be the difference between a leaking cylinder and one that provides a tight seal. This has been proven many hundreds and hundreds of times over with modeling specific gassers. You're not going to get a torque plate on our engines that will make a hill of beans difference in engine performance or block/cylinder plane dimensioning with small gas aero two strokes. What's done during the engine manufacturing process is not generally applicable to the typical top overhaul process. Again, this applies to small gas engines used in our flying machines, not some fire breathing track monster or flat 4 or 6 cylinder engine used in a full scale. |
Last edited by Tired Old Man; 03-12-2009 at 02:18 PM.
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Re: Cylinder Hone for overhaul
So true, but then there are those guys with years of torque in their fingers. They can do without the torque wrench, IF they know how to adjust their feeling to the small size screws in model engines. After a lot of cross checking with accurate tools, I feel I can torque even the smallest screws down to nearly equal.
When I started out on small engines, I used to apply too much torque, and wondered why the heads on the small Honda would not perform as required. Until I bought a torque wrench to educate my feeling. From the onset, the ngine performed as written in the manual, and I learnt that small fry cylinders were no steam pipe flanges! Too much torque is more detrimal to our engines than too little, referring to the operator's feeling. In most cases, just tght is tight enough, understanding the fact that not everybody has access to a well equipped tool shop. Going 'round and 'round will soon yield the feeling that the parts are tight, but not overtorqued. There always will be the debate of tighteng sequence. I found out it does not matter much, as long as it is done little by little, untill everything s tight. |
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Re: Cylinder Hone for overhaul
WELL spoken And the torque for a 5mm .8 STEEL grade 12.9 cylinder bolt is 90 kg-cm...
If you want the lbs/ft you can do your own conversion.... The number is from Zenoah G26 owner's manual, #2075-93111 (409)... |
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California
Joined Jul 2006
4,329 Posts
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Re: Cylinder Hone for overhaul
Pe,
Need a better metric conversion chart than the one I have. I'm guessing Ralph's number above is in the area of 40 in. lbs., or 3.3 ft. lbs. |
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California
Joined Jul 2006
4,329 Posts
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Re: Cylinder Hone for overhaul
Being lazy, I just dial the value in on a torque screwdriver.....
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Re: Cylinder Hone for overhaul
I am one of those who can "feel" the proper torque. I build transmissions, engines, axles, all day and use torque wrenches from 5 oz to 500 ft lb. Can even do it with my impacts. Just today I used a 1/2" impact to zip ring gear bolts to a carrier. Final torque is 75 ft lbs. When I hit the torque wrench on the bolts, all only needed just a slight turn before click. I can do it with most all torque specs. It really depends on the importance of what I am doing but, its all relative. Cylinder bolts? TLAR.
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Re: Cylinder Hone for overhaul
The conversion I use is,,,,,,,, Yep, that's about right. Used to wrench many years ago, kinda like riding a bike.
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Re: Cylinder Hone for overhaul
I'm glad that i found this thread because i have been debating on weather or not to do the cylinders on my dl-100.It has a ring pattern in the jug rather than a crosshatch.Seems that there is some serious debate on this issue.Can anyone tell me why this may a ring pattern and not crossed
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California
Joined Jul 2006
4,329 Posts
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Re: Cylinder Hone for overhaul
Fast and cheap cylinder clean up. They still aren't true when you get them though. If you don't have 65 to 100 hours on the engine there's likely not much point in fooling with it unless the rings have an end gap greater than .015". In that event you would be looking at a new set of rings, but better to replace the entire top if piston/cylinder tolerances are loose.
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California
Joined Jul 2006
4,329 Posts
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Re: Cylinder Hone for overhaul
And you had what else to do?
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