yz450f cam chain slip after engine kick back

4 replies to this topic
  • desert-rat660

Posted August 06, 2008 - 08:14 PM


i had the cam chain slip on the exhaust cam on my 06 yz450f. it was running fine then i shut it off. went back to start it and after i kicked the engine kicked back, then it had no compression. went to kick it again and it locked up.
The bike just got faction mx valves and kibblewhite double valve springs. Its got a JE 13:5:1 piston. the bike had been running good up until this. I oredered a new chain and tensioner. Anything else i should look for? what could have caused this? what can i do to prevent it from happening again? Thanks for those who reply

  • grayracer513

Posted August 06, 2008 - 09:23 PM


How long had the chain been in the bike?

Occasionally, a weak tensioner can cause the timing chain to become kinked, and that could have lead to this. The tensioner cannot be pushed back, no matter how weak it gets. It's like trying to push a bolt through a nut without turning it. But, the tensioner can be so weak that it doesn't tighten the chain enough in the first place.

Other than regular inspection/replacement, I doubt there's any way to prevent it. But it does seem as if it's not particularly common.

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  • desert-rat660

Posted August 06, 2008 - 09:34 PM


i dont really know how many hours the bike has, i took the old chain out and it seems stiff and has some kinked spots. i think the double valve springs might have something to do with it too. lot more effort to turn the cams now. i just recently did the top end and im guessing i should have just changed the chain when i had it apart to begin with. Im lucky the engine wasnt running when this happened or i would be replacing valves again :\.
how do u feel about manual chain tensioners? i dont think they offer one for the 06. thanks

  • grayracer513

Posted August 06, 2008 - 09:51 PM


Manual tensioners require constant attention. I don't don't like them.

The OEM tensioner is a very good, effective, very simple design. Unfortunately, there have been some issues with the latest rendition of it. Hopefully, adjustments will be made in production, and they will once again be as reliable as they were originally.

  • desert-rat660

Posted August 08, 2008 - 07:39 PM


ok the problem was the chain. it was about a 1/4 inch longer than the new one. it was also stiff

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