Vlv Clearance question

4 replies to this topic
  • makncan

Posted June 11, 2010 - 06:47 AM


I have an '03 wr450f, my 1st dirtbike ever. I bought it used a few months ago and just yesterday checked the vlv clearance and most were pretty close to spec maybe just a little bit under spec EXCEPT for the middle intake lifter to cam clearance was next to nothing. I couldn't even get a .0015" feeler under it. the others were right around .004". The exhaust was right around .007"

Rather than get new pads I simply took them to work and ground .002" off of the exhaust and the outer two intake pads which brought me to the high side of the tolerance. Intake tolerance is .004-.006" and exhaust is .008-.010"
However I ground .005" off the middle intake pad and after installing I am still unable to get .0015" between the lifter and cam.

since I was unable to determine the exact gap or lack there of I started at grinding .005" off the pad and since its still tight I plan on grinding off another .005" tonight at work. Is this unusual to have all other gaps be near spec and have one that is way out?

Thanks in advance,

  • grayracer513

Posted June 11, 2010 - 08:12 AM


Your engine needs a valve job. The center intake has worn completely through the hard coating on the valve face, and is wearing into the base metal of the valve head. This is true whenever you have a valve in need of a shim greater than .10 mm thinner than the original build shim, and may be true sooner than that. The center intake usually wears out first because it handles the bulk of the fuel in the intake, which keeps it freer of any deposits, which ironically help protect the faces of the other two valves. Once through the coating the wear accelerates immensely.

Allowing the engine to run like this is to risk dropping a valve head into the engine at speed; an exceedingly ugly experience.

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  • makncan

Posted June 11, 2010 - 08:17 AM


Thanks for the insight, I'll search here on TT and see if there's any instruction on getting it done.

  • grayracer513

Posted June 11, 2010 - 08:46 AM


To start with, obviously, the head has to come off. The best course is to find the shop that does the bulk of the head work for the local dealers and just give him the head and let him do the whole thing. He'll need the cams and associated parts so he can set up the clearances.

You will probably have to provide the parts yourself, since the shop will generally be a small machinist business without a big parts department. The valves will have to be replaced, since they cannot be refinished. The seats do need to be refinished, which is the primary reason you need the machine shop. How well the seats are finished is the key to how long the valves will last.

Before you hear otherwise, you absolutely cannot just drop in a new valve and lap it to the seat, no matter what the manual or anyone else says. It damages the hard facing on which the Ti valves depend, and does a poor job of refinishing the seats.


  • makncan

Posted June 11, 2010 - 05:22 PM


Thanks for all the help!


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