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.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • 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..

Related Content

WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  106 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.