Notices
Gas Engines Questions or comments about gas engines can be posted here

BME 44 losing rpm

Old 12-22-2014, 10:12 PM
  #1  
Meschmidt
Senior Member
Thread Starter
My Feedback: (15)
 
Join Date: Sep 2002
Location: Houston, TX
Posts: 906
Likes: 0
Received 0 Likes on 0 Posts
Default 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
Old 12-23-2014, 10:46 AM
  #2  
av8tor1977
My Feedback: (6)
 
av8tor1977's Avatar
 
Join Date: May 2003
Location: Tucson, AZ
Posts: 7,217
Likes: 0
Received 2 Likes on 2 Posts
Default

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

Last edited by av8tor1977; 12-23-2014 at 10:54 AM.
Old 12-23-2014, 11:03 AM
  #3  
All Day Dan
My Feedback: (5)
 
All Day Dan's Avatar
 
Join Date: Dec 2002
Location: MANHATTAN BEACH, CA
Posts: 4,606
Received 3 Likes on 3 Posts
Default

Av8tr, what is the acceptable ring gap when the ring is not compressed? Dan.
Old 12-23-2014, 11:05 AM
  #4  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Happy Valley, Oregon
Posts: 9,502
Received 172 Likes on 148 Posts
Default

I tend to agree, it's either worn or sticking some. My experience with Saber oil was all bad and that is the biggest factor in me thinking the ring may be worn.
Old 12-24-2014, 03:07 AM
  #5  
Lifer
My Feedback: (1)
 
Lifer's Avatar
 
Join Date: Aug 2008
Location: Kansas City, MO
Posts: 4,520
Likes: 0
Received 29 Likes on 28 Posts
Default

A big plus 1 on the Bowman ring. You might try contacting him and discussing your particular situation. Very nice guy and very helpful.
Old 01-06-2015, 08:16 AM
  #6  
Meschmidt
Senior Member
Thread Starter
My Feedback: (15)
 
Join Date: Sep 2002
Location: Houston, TX
Posts: 906
Likes: 0
Received 0 Likes on 0 Posts
Default

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!
Old 01-06-2015, 11:09 AM
  #7  
av8tor1977
My Feedback: (6)
 
av8tor1977's Avatar
 
Join Date: May 2003
Location: Tucson, AZ
Posts: 7,217
Likes: 0
Received 2 Likes on 2 Posts
Default

Originally Posted by All Day Dan
Av8tr, what is the acceptable ring gap when the ring is not compressed? Dan.
You can't measure a ring that way. The uncompressed gap will vary according to the tension the ring was made with. You have to put the ring in the cylinder, (nice and square and away from port openings near the top), to measure the gap.

AV8TOR
Old 01-06-2015, 12:14 PM
  #8  
Lifer
My Feedback: (1)
 
Lifer's Avatar
 
Join Date: Aug 2008
Location: Kansas City, MO
Posts: 4,520
Likes: 0
Received 29 Likes on 28 Posts
Default

I've installed about 8 Bowman rings, and quite honestly never bothered to measure the gap. They have all fit perfectly and improved the engines performance.
Old 01-06-2015, 02:25 PM
  #9  
Meschmidt
Senior Member
Thread Starter
My Feedback: (15)
 
Join Date: Sep 2002
Location: Houston, TX
Posts: 906
Likes: 0
Received 0 Likes on 0 Posts
Default

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.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.