check valve clearance. only 2 in spec

4 replies to this topic
  • rm125ridwe

Posted August 28, 2010 - 05:44 AM


i bouihgt a used yz450f a while back and havent really rode it only a hour on the meter. it had about 25 on it when i bought it. . any way i check the valve clearances yesterday and im a bit pissed of now.

the bike is only supost to have a hand full of hours on it and it was overall clean other then plastics, event he linkage bearings where packed with grease.

anyway here is the valve clearances.

0 0
.23 .18

0 0 0
zero .10 .30
195 181 160 shim pad size

i have no clue why the orginal owner put these shim pads in but do i have anything to worry about with the excessively large gap (.30mm) in the right valve. the only thing that should change is how late the valve opens right? i doubt i have to worry about piston contact since .15mm isnt that big of a gap but i could be wrong. im just going to order a 175-185 shims and that should get me in the ball park. didnt have a chance to see what the shims where in the exhaust side yet. just venting a bit pissed off that some one is that incompten to set the valve clearance that far off. funny part is i bought the bike from a little racing bike shop that sponsers a few of the local series. and not to mention that the valve caps had to be over torqued i could harley brake the bolts lose with a twrench.

  • grayracer513

Posted August 28, 2010 - 11:13 AM


The right and intakes need to be corrected, no question. Running valves out of spec is never acceptable. Interestingly, correcting them will put the shim sixes back in the range it would have been built with: 180-185 in both cases. Shoot for closer to .10 than .15

The exhaust at .18 should also be corrected while your at it. Out is out. This could be a simple case of settling into the seat, as sometimes does happen.

After shimming, check fairly frequently for a few times to see if it holds at the clearance you set. If it does, you're OK, if it keeps closing up, it's not.

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  • brentn

Posted August 28, 2010 - 05:36 PM


What does it mean when the valves keep closing up or expanding in clearance, what is exactly happening and what is the outcome?

  • Just_a_trail_rider

Posted August 28, 2010 - 10:35 PM


Well... the valves will probably get tighter rather than looser. I think that the valve seats will wear out more than the valves themselves. When that happens, you'll have to take the head to the machine shop and get new valve seats cut for it and possibly a couple of new valves. Around here that is about about $500 worth of work and parts.

  • grayracer513

Posted August 28, 2010 - 10:35 PM


Only in rare and unusual circumstances will the clearance increase. When the clearance decreases relatively quickly, it means the hard coat on the valve is worn through and they need to be replaced before they cause major damage.

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