when is time for valve job?


2 replies to this topic
  • mdsharon

Posted July 14, 2014 - 07:17 PM

#1

  Lots of hours on bike 08 yz450 the exhaust valves are fine, but the intake have been adjusted a few times now the middle intake is at 130 shim .The shim kit only goes to 120 so figured it will need it soon. Outer intakes still at about 160-165. what do you guys think? Would hate to grenade it..



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  • grayracer513

Posted July 15, 2014 - 06:58 AM

#2

Time to go through that head.  Titanium valves are dependent on an extremely hard, extremely thin coating for their resistance to wear.  Without it, they won't hold up.  Once the valve has been adjusted to a shim size more than .10mm smaller than it came with originally, you can figure that it's shot.  This is especially true if the interval from one adjustment to the next gets significantly shorter.  Time from new to the first adjustment is often well over 200 hours, but after the second one, you might find that they will only go 5-10 without being reset.  That clearly indicates that the hard coat has worn through, and the valves need to be replaced.

 

Failing to take care of this in a timely manner can result in the valve breaking at the stem and dropping the valve head at high speed, which is normally catastrophic.

 

ALWAYS have the seats professionally refinished when replacing the valves, and NEVER lap a titanium valve. 



  • mdsharon

Posted July 18, 2014 - 09:18 AM

#3

Thanks kinda what I thought time  to take head to shop.  :thumbsup:







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