Hi Folks,
This may be a stupid question but I'm not sure whether valve clearances increase or decrease over time? I just checked the valve clearances recently and both exhaust valves were on the smaller end of the gap specified. A freind of mine told me that you have to be careful that the exhaust valve clearances aren't below the specified gap or you may burn a valve/seat. Is this true and if so presumably I should check tha they don' t tighten up soon? Thanks for any advice on this but I always thought that clearances got bigger not smaller!
The clearnace we measure will decrease with wear. The valve will actually wear into the seal cut into the engine head, which makes the valve stem ride closer to the bucket adn the bucket closer to the cam. We measure the gap that should exist between the lowest or shortest side of the cam lobe and the top of the bucket.
If clearance is too tight, as will eventually happen with normal wear, damage, or misadjustment, the valve will not come all the way donw to rest on the seat long enough to lose its heat to the head. The valve then gets too hot and erodes rapidly. Thus, tight valves get tighter quickly. But, if you get 'em too loose, the valves will not be open long enough to let the engine "breath".
prs