valve shims

10 replies to this topic
  • rocky1980

Posted October 30, 2014 - 12:12 PM


hi guys iv finally got around to checking my valve shim measurements today the exhaust is in spec but the intake i can't get any gauge under it at all i took the shim out and 2 are 180 and one is 185 what size would i need to get them in spec?

  • grayracer513

Posted October 30, 2014 - 12:24 PM


Can't answer that question because you don't know what the clearance (or interference) is yet.  You'll need at least one 175 or 170 to start with.  Insert that shim under each valve and recheck the clearance.  To speed up the process, don't bother to connect the cam chain, just place the cam in the saddle and torque it to 3-4 ft/lb (36-48 in/lb).  If this gives you some amount of clearance, you can use that measurement to figure out what shims to put under that bucket.  If there is still no clearance go to the next smaller size and recheck.


The problem is that once the valves go that far downhill, they can actually wear past a zero clearance condition.  This is in part because the head expands more than the valve does, and clearances are actually greater when hot than when cold. 


You should be aware that once a valve requires a shim more than two sizes (.10mm) smaller than its original build shim, the hard coating on the face is gone, and that valve needs to be replaced, and you will find that it will be out of spec again after only a few more hours of operation. 

  • rocky1980

Posted October 30, 2014 - 12:31 PM


thanks for your help again gray i have ordered both them sizes ill see what they come back as once there fitted.

its my own daft fault its just done a top end rebuild and i didn't check the clearances whilst the motor was out due to excitement of getting it in and started fast :/  i have a feeling this is going to be costly lol

  • rocky1980

Posted October 30, 2014 - 12:35 PM


so as a worst case scenario if the valves do need renewing is there any other work i have to do to the head or can i just drop the new valves in?

  • grayracer513

Posted October 30, 2014 - 09:23 PM


Year model?

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  • rocky1980

Posted October 31, 2014 - 01:02 AM


2003 yz450f 

  • grayracer513

Posted October 31, 2014 - 06:49 AM


Titanium valves.  You will need to take the head to a competent small engine machine shop to have the valve seats refinished.  Just dropping new valves in is an almost certain way to get them to fail early.

  • rocky1980

Posted October 31, 2014 - 09:27 AM


thanks gray looks like another costly job for this you know that feeling where u wish u never started!

  • rocky1980

Posted November 01, 2014 - 03:13 PM


hi gray today i checked my clearances with 170 shims 2 where still tight so i changed to 145 as a base line as there the only ones i had heres the results.


left = 004 with 170 shim installed

middle = 008 with 145 shim installed

right = 008 with 145 shim installed 


my question is for the left should i leave this or bring it to the 0.15 range?


secondly what size shim would i need to bring the middle and right into range i was thinking 150 or maybe a 155? 

Edited by rocky1980, November 01, 2014 - 03:16 PM.

  • grayracer513

Posted November 02, 2014 - 07:01 AM


You need to replace those valves immediately.  If you keep running them, you will at least damage the valve seat so that it needs an extra deep cut to be refinished, and there is a very real possibility that one of them will break off in the engine at speed and completely destroy the whole top end.

  • rocky1980

Posted November 02, 2014 - 07:09 AM


bloody hell think ill get rid of it its cost more than its worth already without buying valves oh well back to the good old cbr lol

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