BME 44 losing rpm
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BME 44 losing rpm
I have a 15 year old BME 44 (Echo) I've had since new. It runs fine but loses 800 - 1000 rpm from peak after running awhile. It has been in a WM Zero 14 years and never had cooling issues. The compression is really good and using Amsoil Sabre at 75:1. I rebuilt the carb a couple of times but no change. Even checked timing and tried another ignition. The engine bearings seem ok. It will run a full flight and has never quit so It is not overheating or getting too hot. It has gotten worse over the last few years I have never pulled the piston out of the bore since compression does not seem to be a concern It really looks clean thru the exhaust and carb port and on top of the piston and rings. Will buildup of carbon in the combustion chamber cause this problem? I'm stumped. Thanks, Paul
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Your ring(s) are most likely worn. I have seen engines that seemed to have great compression, and that ran and handled perfectly, be down on power due to worn rings. The ring gap on these little engines is supposed to be really tight, like around .003" which is the thickness of a piece of paper. I would bet if you pulled your engine apart it would have a much larger ring gap. I have seen engines like this gain 800 rpms with only a ring change. The best rings around, better even than original, are made by Frank Bowman, and cost only $11.00. They are high performance rings made of a superior cast iron, and seat quickly and almost always give an engine a performance boost over original. Some people even replace brand new rings with Frank's for the best performance.
(On engines with two rings, I generally leave the stock second ring in place, and only replace the top ring with a Frank Bowman ring. Only one is needed.)
Frank Bowman: [email protected] 505-327-0696
AV8TOR
(On engines with two rings, I generally leave the stock second ring in place, and only replace the top ring with a Frank Bowman ring. Only one is needed.)
Frank Bowman: [email protected] 505-327-0696
AV8TOR
Last edited by av8tor1977; 12-23-2014 at 10:54 AM.
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I took the engine off the plane and pulled the crank and piston out. Found the second ring stuck in the groove. The top ring was floating in the groove fine. Soaked the top of piston in laquer thinner to get the second ring free. Scrubbed the ring grooves and rings with a toothbrush. No crusty carbon buildup in combustion chamber or grooves. Just a sticky residue that will wipe off with rag and thinner. I think the Amsoil is ok to use as his engine has hundreds of flights. Miked rings with caliper and checked consistent. Could re-use them but have heard so much about the Bowman rings. Have Bowman rings on way and will replace top ring only and use old second ring as reccomended. I have another 12 year old BME 50 that seems to be slightly down on power too, so I'll check that one out the same way. Thanks for all your help as ya'll were right!
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I was checking the ring width to see if the top one was worn more than the bottom with the caliper. They both measured the same all around. I'll keep one as a spare.