bent valves?

4 replies to this topic
  • Bigdong

Posted December 01, 2012 - 06:15 AM


A bike that a friend bought died the other week and we ended up after measuring the piston rings deciding it was way out of spec so replaced them and rebuilt. As we were doing the strip down when trying to change the oil filter the bolts opened with a Crack, Not good we thought. On inspection of the oil filter it became apparent that the bike, (09) has never had the filter changed as it was collapsed in. We continued anyways and when trying to set timing we lined the intake with the flywheel at tdc and we got the 13 pins in between but the 9 oclock and 3 oclock dont line up perfectly. stretched chain?

Also to finish things off when we measure the intake clearances it was showing 0.80 mm, could this be the valves bent or just from general bad maintinance that its got this far?

We re shimmed anyways but all we can get is an occasional backfire like timing is out.

When we had it apart we did have a look at the head and everything looked ok but we never had valves out and there was no obvious marks on the piston from hitting.

Im also aware that the oil/filter and valves should have been checked when we got it but this one never.

Edit:- ok got bike running but it was 12 pins in between not 13, does this mean chain has stretched?

Any ideas


Edited by Bigdong, December 01, 2012 - 10:26 AM.

  • crf450319

Posted December 02, 2012 - 07:42 AM


If I were you (or your friend) I'd spend the $20 and put a new cam chain in the bike, I replace mine every 50 hours of runtime.

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  • grayracer513

Posted December 02, 2012 - 07:50 AM


In the first place, the timing IS NOT set by counting pins between the cams. That's only a cross check and an assembly aid.


12 pins would be incorrect for any YZ450 up to '10, however.

The excessive clearance could be caused by bent valves, but also by damaged cam bores.

  • Bigdong

Posted December 02, 2012 - 08:19 AM



Yeah i realise you dont count the pins, its just the fact that once timing was set i was confused at to why we only had 12 pins instead of 13, 1 tooth one way or the other would make things worse. Hes ordered a chain now anyways. Im still not sure on the valves though.we checked the cam bore and its fine. Would the bike run with bent valves?

Edited by Bigdong, December 02, 2012 - 08:21 AM.

  • grayracer513

Posted December 02, 2012 - 11:42 AM


Maybe, but not well, and you run the risk of breaking a valve stem off.

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