comp. leak

Originally posted by 125 rider
Someone else has told him that his problem is that the compression is leaking right out of the crack in the pipe.

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that someone else has BS leaking out of the crack in his face!

you are right, the pipe should have little to do with compression, but a lot to do with how the bike runs. It sounds like the dude either did a bad job of installing the top end (eg dirt) and an equally bad job of break in and the top end is worn out already.

Maybe you should suggest he buy a book on motorcycle maintainance (there is a good one for dirt bikes by eric gorr) and have another look at the top end (when the bike is clean), he might be able to get awy with new rings.

But it also might be that he got a wrong size piston or the bore is worn and needs the next size pistion, if he takes everything apprt and gets it all measured that will hhelp, if the top end is looing compresion the piston will slap a lot within the bore and things can get very ugly, very quickly!

it will never work properly with a cracked pipe either!

How does he know he is getting low compression did he measure it or does he think that because it is not running right now. Like bclapham said a cracked pipe will not alter compression but could make it run as you described. make sure to do a compression check with a guage dont just take it for granted

This happened to me and a friend with his 80. Same situation, bike started and ran for like 5 mins, then no comp. There was about 1/8" of piston to cylinder clearence. I took the old piston and sanded all the carbon off the top. It was a 1mm oversize.