chewed a valve, should I split the case?

2 replies to this topic
  • ACM

Posted October 21, 2011 - 06:21 AM


I've chewed a valve in a YZ450F. I have the engine on the table with the top end removed. Is it wise to also split the case and inspect, almost by routine, or would I be best advised to leave it alone unless something's obviously broken?

I've had a look around and I can't find an answer to the below, can anyone help?:

My (wifes) 2009 YZ450F chewed up a couple of valves. It was pretty extensive, resulting in one valve head being wedged sideways into the head, another bouncing around in the cylinder, and various bits of valve stem making their way into the exhaust header. It looks like I need a new piston, cylinder, cylinder head and at least 3 valves, not sure about cams.

When it happened there was a automatic hammer noise for a few seconds, after which the engine would not turn over. It would however turn freely until it got near TDC.

I've now taken the engine out the bike, and removed the top end. There was a valve head wedged sideways into the head, and the piston was hitting this near TDC. With the head and cylinder removed the engine appears to turn over no problem.

So, given it's on my table, should I just split the case for a clean out and inspection if nothing else, or should I let sleeping dogs lie?

My mechanical skills are willing amateur at best, but I'm not in fear of changing the top end and putting the engine back in the bike. I have a full engine gasket kit, a service manual, a pound-inch torque wrench, and have bought a 2007 top end on ebay for those parts.

Thanks for any advice you guys can give!


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  • MxSkater86

Posted October 21, 2011 - 06:32 AM


Personally I would. Especially if you already have it most of the way apart. Even if you didnt find anything it would probably benefit you to clean the oil screen inside the cases anyway. Its better to do it now instead of later because if something is down there then you might have to tear it apart again.

The only thing I can think could be wrong with the cams is that the gear spun on the cam. If it locked up instantly while you were on the gas it could have done this. Happened to my current 06 450 I have now

  • grayracer513

Posted October 21, 2011 - 06:49 AM


Since the piston collided with a valve, it's possible that the rod is bent, or the crank misaligned as a result. Can't hurt to have a look.

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