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Message: [QUOTE="flyincat, post: 607443, member: 43178"] I just found this forum and after reading some posts, this is the most knowledgable crowd around so I need your help. To make a long story short, I bought a 98 cr250 and blew it up after about an hour on the first ride. I was told that it was a stock engine but when I tore it down I found a sleeved cylinder and a wiseco piston. Well I got the cylinder bored and all new top end. It fired right up so I thought I was all set. Then the mystery begins.... I heard a knocking/clanking noise in the top of the engine when I let it idle a little to break it in. I'm obviously not an engine expert but I wondered if it could be detonating and it sounded real lean (which could be a leaking seal, another potential problem). I tore the carb apart and cleaned it and found all stock jets in it. So I fired it up again and it was still knocking. I did a compression check with two gauges and both read 240psi!!!! What the heck is going on? I'm almost positive the head wasn't cut at all so I have no idea why the compression is so high. I still haven't got a consistent answer on the compression for the stock bike. I was told anywhere from 130psi to 235psi after a rebuild by dealers and local shops. As far as the knocking, I am starting to believe that the piston might be hitting the head stightly because I can hear a faint sound when I rotate the flywheel. As far as the high compression, the only idea I have left is that the sleeve is not positioned right. Could the Cometic head gasket be the wrong one? Is this compression even too high to run race gas? I was thinking I was going to use high octane pump gas since I thought it was stock. Give me all you guys got because I'm lost. [/QUOTE]

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