2007 YZ450F with 1 Different Valve?

11 replies to this topic
  • mxman47

Posted May 22, 2015 - 12:39 AM


I was doing a valve adjustment on a newly acquired bike and the intake valve closest to the timing chain measured .40mm clearance. Upon lifter removal that valve looks like it is different. It doesn't sit as high out of the keepers. Is this common? It also looks a little bigger in diameter than the others. I also noticed a blue mark on tge head by that valve.

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  • grayracer513

Posted May 22, 2015 - 06:16 AM


That valve has a damaged stem tip.  The hardened cap of the stem has failed and the stem has "mushroomed".  Needs to be replaced.

  • mxman47

Posted May 22, 2015 - 09:56 AM


Thanks gray. What would cause it?

  • grayracer513

Posted May 22, 2015 - 10:00 AM


Probably just a bad part.

  • mxman47

Posted May 22, 2015 - 11:07 AM


Will it be ok to shim it for now?

  • grayracer513

Posted May 22, 2015 - 11:59 AM


I wouldn't.  Ever seen what happens when one of these drops a valve at speed?  Me$$y.

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  • mxman47

Posted May 22, 2015 - 01:56 PM


Ok so it's looking like I need to buy a set of valve springs, a valve, stem seal, stem guide, and have a machine shop cut the valve seat and valve guide. Does that sound right?

Edited by mxman47, May 22, 2015 - 01:57 PM.

  • grayracer513

Posted May 22, 2015 - 02:35 PM


You probably don't need the guide (see what the machinist says), and you'll want all 5 seals.

  • mxman47

Posted June 11, 2015 - 09:28 PM


The head went out to Dave at Mxtime with a set of new oem valves springs and seals. I took it to my local Yamaha dealer and wasn't too impressed with their tooling and method for cutting seats, especially considering the premium $72/hour labor. Not to mention the price they charge for the parts.

I also picked up a new oem piston kit with gaskets and timing chain. Really looking forward to getting it up and running again. I've gone through the forks, shock, all swingarm and linkage bearings, new updated stem bearings, and carburetor since I've been waiting.

Edited by mxman47, June 11, 2015 - 09:29 PM.

  • mxman47

Posted June 11, 2015 - 09:33 PM


Also, I didn't find the hardened tip anywhere. It's not magnetic so it would stick to the magneto. And I didn't see it when looking into the "sump" with the mag cover off. Any ideas? I don't want it the find the gears or crank before I find it.

  • grayracer513

Posted June 12, 2015 - 07:44 AM


Might not be anything left of it.  It may simply have worn through the hardening and then downward.

  • mxman47

Posted June 19, 2015 - 08:20 PM


Got it running today. Everything turned out great. Thanks for the insight grayracer

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