2000 yz426, valves are to tight to get a reading

2 replies to this topic
  • disccat

Posted October 09, 2013 - 12:09 PM


First question, rode the bike and noticed it leaking some oil. Saw some other posts said it's probably over fill issue. Any way parked and hav'nt rode for over two years. Finally want to start riding again and can not get it to start at all. So I pulled valvre cover to check valve clearance. Could not even get  a feeler into the intakes at all. So pulled camshaft and found each valve had a shim of 1,7 under each bucket, After reading everything I can find, 1.2 is the smallest shim I can find. just wondering what else I might look at before buying a complete shim kit. What would make the valves so tight?

Any help would be great.

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  • grayracer513

Posted October 09, 2013 - 01:20 PM


Wear is what makes them tight.  As the face of the valve wears, the top of the stem moves closer to the camshaft.  That will continue until the clearance is zero unless something breaks.  Because the aluminum head expands more than the steel of the valves does, a valve that wears to zero clearance at operating temperatures can actually have negative clearance when cold, and the valve may need a .5mm smaller shim just to get the valve to close all the way. 


If you have that much less than the specified valve clearance, it's probably time to rebuild the head.

  • jamracing

Posted October 09, 2013 - 01:38 PM


Sounds about right... However, you can take a chance and throw in a really thin shim and maybe you'll be OK...
Personally, I'd take the head off and rebuild it..

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