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bown top end

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i have an 06 crf250r and was at the track bike ran fine all day then towards the end of the day i came of a jump gave it some gas and i heard a wineding noise followed by a backfire and it died now it has no compression at all just wondering if anybody knows exactly what happend and what i need to change thanx

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yeah open her up. it's not that hard just get a manual. could be a number of things. you probably dropped a valve and f*****ed up your piston and cylinder. have a couple beers and perform some surgery!

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just tore her down found the right exhaust valve stuck open and hit the top of the piston but just knicked it what exactly do i need to replace besides the piston i was thinkn about putting a athena big bore kit would that pretty much fix it all?

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just tore her down found the right exhaust valve stuck open and hit the top of the piston but just knicked it what exactly do i need to replace besides the piston i was thinkn about putting a athena big bore kit would that pretty much fix it all?

Be very careful here... That "nick" on the piston put a phenomenal amount of side shock on the connecting rod. I and a few others have had the top end of the connecting rod crack and even break off because of breaking a timing chain and having valves strike the piston top or the same thing because of breaking a valve spring or loosing a valve stem keeper. Race pistons have almost no skirt to keep the sliding friction to a minimum, and any side loads can cock the piston sideways stressing the connecting rod. The fact that you mentioned only one valve striking the piston top makes your failure even more likely to have stressed the top of the connecting rod due to the sideways stress the valve put on the piston.

Not to put a damper on the discussions, but I would not only rebuild the valve train - there is a good possibility that the exhaust valve was bent during contact, necessitating, at minimum, replacement of that valve and valve guide. This is a great opportunity to replace the exhaust valve(s) with Kibblewhite SS valves. I think the machining quality, coatings and tolerances of the KWs are actually better than stock.

The piston, wrist pin, rings are obvious replacement parts, but I would take a really close look at the top end of the connecting rod.

BTW: You might consider getting a $250 replacement crank assembly just to be on the safe side. If the top of the rod breaks, it usually lays down and punches out through the right side engine case making a major mess and one expensive repair. Parts alone for this type of rebuild can run $750+.

As far as going with an Athena kit... it is a great upgrade, but I would never put one on with a questionable crank due to the extra power loads.

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