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Has anyone seen this happen before?! What can cause this. 2009 YZ250F. All stock. 45 hours. Havent split the cases yet but wow...

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well i bought this bike on tuesday. guy said it had a loud noise and just wanted to get rid of it. i started it briefly when i got it home but immediately shut it off. it sounded like there was an elf inside the case trying to break his way out with a jackhammer haha... i just hope there wasnt too much case damage. the one lobe is completely separated from the crank. the only think holding it in there is the fact that the crank housing is circular

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yummy, whats the top end look like? thats what usually heps me. is there alot of black junk around the piston and inside the cylinder? that will tell you if he rode it entirely too hard or not. this happened to a buddy of mine. its probably best to rebuilld the whole thing depending what the gears and clutch plates look like. check out your clutch plates and basket and it should be easy from there to determine what to do. :smirk:

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everything else besides the crank looks good. at least on the top end. guy said it was just rebuilt 45 hours ago by dealership. new clutch, suspension, valves, piston....the bike is in beautiful shape. got a steal at $1700. ordered a new crank, bearings, and gaskets last night. should be an easy fix if the cases arent shot. we'll see. either way for that price i think i come out ahead on this one!

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well if you don't have a visible crack or hole in the cases right now you should be ok, you might have some scarring inside - just smooth that out before you reassemble everything, that's a very strange break, almost looks like a defect of sorts in the casting - might be worthwhile shooting Yamaha a picture of it - maybe they will send you a free crank.

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All of that was rebuilt on an 09 bike, then you find the broken crank...... I'd be a bit wary and go through every nut, bolt, fastener, and bearing on the entire bike. Sounds like it was riden HARD.

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Very possible that is was just a casting flaw and it finally just let go. Very rare but I have seen it happen on cars. These engines are like single cylinder formula 1 engines if you think about it. Amazing they stay together in the first place. Some great engineering in these bikes if you ask me.

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