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engine diagnosis

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hey guys,

I would post this in the suzuki 2 stroke but the responses there are very limited so i'll post it here. I have a 2003 RM85 and it seems to have a problem. There are a few symptoms and things that make me think something is wrong but it could be im just biased towards my $10,000 RM85 that sits on the other side of the garage. So, let me give you some background information, the bike is bored out to 100cc (52mm) and has a FMF fatty pipe. everything else is stock engine wise. When you rev the bike, it seems to rev REALLY quickly and the whole engine rattles and seems like its "unbalanced". Its been smoking excessive lately too (blueish white smoke) I just reringed the piston so its good and the cylinder is too. cleaned the power valve today so the problem doesnt lie there either. ive owned the bike for about 7 months and im not sure if the bottom ends ever been rebuilt but i do know this bike has been a race bike all of its life. What could the problem be??

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Pull topend off and Mic your cylinder and check squish. Also, make sure your motor mounts are strong.

I'd start there.

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First, check all the simple stuff. Are your motor mounts tight? Does the bike have a head stay? etc. Pull the ignition cover off and grap the flywheel--any up and down play means a new bottom end.

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Pull topend off and Mic your cylinder and check squish. Also, make sure your motor mounts are strong.

I'd start there.

What does that mean?? haha sorry im still learning. Im only good with the basic maintenance and engine building. :)

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First, check all the simple stuff. Are your motor mounts tight? Does the bike have a head stay? etc. Pull the ignition cover off and grap the flywheel--any up and down play means a new bottom end.

what is that??

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Have you cased any jumps really hard lately? Sometimes the crankshaft can shift out of true on a hard impact. This will cause it to shake like its out of balance and can damage the main bearings and seals allowing tranny oil to enter and burn blue smoke.

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to MIC something is short for use a micrometer to check the cylinder bore for tolerances and out of round conditions. If ya had your motor built by a race motor builder, he knows what tolerance he built the engine to. Squish can give ya a good indication of lower bearing wear. Ya might not be able to feel it at the flywheel. I think you're running about as big of a bore as that bottom end will handle. So, my assumption is that it was a full-bore race motor, and you were running the ragged edge of performance vs reliability. Prolly ran like a bat outta hell, for a short while though. If all your motor mounts are strong, I'm suspecting that your full-bore race motor has eclipsed it's cycle time.

BTW, a head stay is the part of the cylinder head that is attached to the frame of your bike. Some bikes don't have them, I believe your model does. Could be wrong though. If not, I could imagine that getting one would be to your advantage, but I don't think it's your real problem. I'm guessing crank bearings, seals, etc

Hope this helps

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Have you cased any jumps really hard lately? Sometimes the crankshaft can shift out of true on a hard impact. This will cause it to shake like its out of balance and can damage the main bearings and seals allowing tranny oil to enter and burn blue smoke.

thats funny, ive actually cased a 70 foot gap twice and landed HARD on the frame rails. this may be my problem!!

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to MIC something is short for use a micrometer to check the cylinder bore for tolerances and out of round conditions. If ya had your motor built by a race motor builder, he knows what tolerance he built the engine to. Squish can give ya a good indication of lower bearing wear. Ya might not be able to feel it at the flywheel. I think you're running about as big of a bore as that bottom end will handle. So, my assumption is that it was a full-bore race motor, and you were running the ragged edge of performance vs reliability. Prolly ran like a bat outta hell, for a short while though. If all your motor mounts are strong, I'm suspecting that your full-bore race motor has eclipsed it's cycle time.

BTW, a head stay is the part of the cylinder head that is attached to the frame of your bike. Some bikes don't have them, I believe your model does. Could be wrong though. If not, I could imagine that getting one would be to your advantage, but I don't think it's your real problem. I'm guessing crank bearings, seals, etc

Hope this helps

thanks man, i think its a combination of what you explained and the jump casing. thanks again to everyone who replied

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