Valve Adjustment

[matadorCE]

Good question, but, No. Shims really don't wear to any appreciable degree. However, valve faces and valve seats do wear and get pounded down over time, which causes the clearances to get tighter. Going to the loose end reduces the chances that the clearances will drop dangerously low before the next checkup.

Ok thanks for the great info. The shims must be designed to wear different on car engines since anytime I've checked and adjusted clearances I've aimed for the mid range and end up using a mix of old and new shims

 

[acruhl]

Yeah good point. I think it's still too hard to adjust to the range though. Mine are out of spec now where they were in spec before the adjustment, although on the limit.

 

[ReidMcT]

Mine are out of spec now where they were in spec before the adjustment, although on the limit.

I appreciate the discomfort at finding a clearance at the limit, but changing a shim to deliberately put the clearance beyond the limit??

Imagine you were just starting the job to check your valves, and you found that one was out of spec. Wouldn't you feel the need to change the shim to bring it into spec - even if the available shim increments only allowed you to set the clearance at the limit of the range?

 

[acruhl]

Yes. Math vs. reality. My intakes were right at the .08mm lower limit. I put in a shim that was .05mm smaller by math, and by the tolerance of my measurement tool, but in reality my clearance now measures .13 and .14, slightly above the .12 upper limit. The other problem is the factory shims don't seem to be right on the .05 increment of the shim kit I bought. So I could have used one of my shims to get maybe .01 or .02 mm more clearance, but there's not much point in doing that. Different points on the cam might be bigger than that clearance. Better to just make them loose because they are going to come back anyway.

I've adjusted lots of valves. This happens.