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2010 YZ250F broken crank rod

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I recently bought a 2010 yz 250F bored to a 269. This past weekend, I took it out to ride for the first time. Before riding I inspected valves, changed the oil, replaced the oil filter, cleaned the air filter, etc., everything was ready to go. I got out for 4 20-minute practice sessions, bike ran great. Then the 5th practice session, I went out for 2 laps, and while approaching a jump, the bike made a terrible noise that pretty much sounded like somebody grinding something with a bench grinder. Took the bike home and removed the top end down to the cylinder. The crank rod is completely snapped right at the big end, the cylinder has a big crack right at the bottom of the sleeve, the piston is obviously destroyed, the crank balancer shaft is broken in half, and from the looks of it a chunk of my inner cases is missing too. Needless to say i'm pretty f**king pissed. The bike was supposedly completely rebuilt from the bottom up and since been ridden 5 times for a total of 10-15 hours. My main question is: What causes the crank rod to break like that?? Thanks in advance.

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Did you change the oil after the break in? Last thing you need is little metal particles floating around clogging oil passages. Not saying that was the cause, just throwing out possible ideas. Another possibility is that the low end was not rebuilt correctly i.e. A bearing installed incorrectly or defective parts. Is anything seized?

Can you post pics?

I know bikerdude and nokickstandsallowed just went thru some major lower end tragedy so you might want to PM them a link to this and see if they have some words of wisdom.

I could see how you'd be pissed.

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I bought the bike rebuilt, I didn't have anything to do with the break in, etc. I just changed the oil when I bought it to be safe. The mechanic who did the work is a local guy who is also andrew short's old mechanic, so I would assume he would know what he is doing.... Either that or the kid who sold me the bike lied and the bottom end has never been touched. I can't see the rod snapping in half on a 10-15 hr old crank.. and yeah I will try to post some pics today.

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Sounds like he lied about the crank being replaced. But I do believe that is a weak spot for these cranks. I bought a 250f blown up that had that exact same thing happen. But it could have also been a defect in the crank

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Are you using a synthetic.. I just rebuilt a bottom end for a buddy. he had old non synthetic oil wound out on a gravel road and the rod went. I tell him now to break it in with a non syn and switch it to syn when he is winding it out and for god sakes keep the oil clean.. I would guess yours was worn but consider the oil too. good luck

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well, freak things do happen, but I never believe anybody unless I see receipts. Anyone who is good about preventative maint. keeps receipts, for service records. Its also a good case for fraud and refund of your money if you were deliberately deceived. Did you take seller at his word or did you see receipts?

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its a common fault for 2010 cranks snapping, i never seen one go but have read up that they have been snapping. so to me the lad lied about having new crank.

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I agree, probably a used crank. Plus you don't know if the previous rider hit the rev limiter every 2 seconds like Justin Barcia on his CRF......good lord I would hate being that kid's mechanic...

Also the added mass of the bigger piston may have had something to do with the connecting rod's premature failure. I would say the rev limit needs to be reduced with more mass flying around, and I am willing to bet nobody messed with the ignition curve/rpm limit.

250F's regardless of make are probably the hardest bikes on parts because they need to spin so darn high. I would imagine a crank would last more than a year, but at 16,000 rpm, nothing ticks, it just goes BOOM before you hear anything wrong.

I hope you get her fixed soon and remember: It's only money, you'll make some more tomorrow. At least you didn't get hurt, that takes much longer to fix.

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I agree, probably a used crank. Plus you don't know if the previous rider hit the rev limiter every 2 seconds like Justin Barcia on his CRF......good lord I would hate being that kid's mechanic...

Also the added mass of the bigger piston may have had something to do with the connecting rod's premature failure. I would say the rev limit needs to be reduced with more mass flying around, and I am willing to bet nobody messed with the ignition curve/rpm limit.

250F's regardless of make are probably the hardest bikes on parts because they need to spin so darn high. I would imagine a crank would last more than a year, but at 16,000 rpm, nothing ticks, it just goes BOOM before you hear anything wrong.

I hope you get her fixed soon and remember: It's only money, you'll make some more tomorrow. At least you didn't get hurt, that takes much longer to fix.

They rebuild the engines after every race so it doesnt matter. I wonder what would happen if they installed an extreme high rev limiter would he still hit it?

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Called the mechanic that did the work today. Sure enough, he says he does not recall putting a crank in the bike. This is complete bulls**t. Now I am left with well over $1000 in damage done to a bike that I just bought less than a week ago. Not to mention the fact that the guy lied to me about replacing the part that broke.. I'm definently going to try to get some money out of him to help fix this thing!

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Called the mechanic that did the work today. Sure enough, he says he does not recall putting a crank in the bike. This is complete bulls**t. Now I am left with well over $1000 in damage done to a bike that I just bought less than a week ago. Not to mention the fact that the guy lied to me about replacing the part that broke.. I'm definently going to try to get some money out of him to help fix this thing!

If you have his add and can get a signed affidavit from the mechanic tell him he can either refund the $$ or you will take him to small claims court. If he failed to give full disclosure at the time of sale, that is illegal.

Good luck.

Edit: Unless he can come up with the work order stating the crank was

repaired/replaced to new bike specs.

Edit 2: If the mechanic is a business owner he should have a copy of the work order or at least a parts list of what was replaced on the bike.

Edited by psmcn

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I called him and he says "Oh no, I never said we put a crank in it, we just put in cams and the 270cc bore kit." So he's already trying to lie about it and unfortunately, I have nothing in writing form him to prove he said it did... I can quote him word for word on what he said when he told me it did have a new crank, but still nothing in writing...

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I called him and he says "Oh no, I never said we put a crank in it, we just put in cams and the 270cc bore kit." So he's already trying to lie about it and unfortunately, I have nothing in writing form him to prove he said it did... I can quote him word for word on what he said when he told me it did have a new crank, but still nothing in writing...

Bummer!

You may try looking for a used motor instead of rebuilding the blown one. It may be cheaper to rebuild an intact salvage motor then the one you have. With out a complete tear down you do not know the full extent of the damage yet. When things that spin really fast make crunchy sounds while running it is never good for the entire motor and trans.

Good luck!!

Paul

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You know what really sucks is that I found a brand new take off motor from a 2010 YZ 250F on ebay that sold for $1275 but I missed the auction.. :thumbsup::banghead::ride::worthy::bonk::worthy:

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There was a thread on here months back that a guy installed a WR motor with electric start and YZ transmission for racing into his aluminum framed YZ. Came out pretty trick. Just throwing that out there to get the ol' noodle a spoolin'

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print out this thread, get something in writing from mechanic, document your call to him and the mechanic, and file a small claims suit. It sounds fraudulent to me

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print out this thread, get something in writing from mechanic, document your call to him and the mechanic, and file a small claims suit. It sounds fraudulent to me

How does he prove that seller "said" there was a new crank installed?

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^^ Exactly, i have nothing in writing from the seller saying that he put one in, so I really can't do anything about it outside of him and I. And I finally got the cases split, how do I post pics to the thread?

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