I can safely say that the intake valves get tight, because 5 out of 6 of mine (Triple 955/595) have zero gap. However, is this also the case with the exhaust valves, or do they get progressively wider (though I guess this wouldn’t make sense), with only one of my exhaust valves being on the edge of spec by being on the wide range. The reason I ask is I have the head off and the opportunity to switch a few shims around to get the best out of the tolerances over the long term.
Thanks, TD, I know it seemed an obvious question, but I just wanted to check because one of the exhaust clearances was borderline out of spec, making me think it was either a wrong choice or that the gaps increase in the exhaust? Clearly then the best option is to have them shimmed at their widest specification if there are shims going begging? Many thanks again!
As TD has said, clearances reduce with use, not due to cam/follower wear so much as the fact that the valves hammer down into the seats but it can vary massively between different engines which is why some specify long valve clearance check intervals. I always aim for a clearance some where in the middle of the specs. In theory, setting them at max reduces valve lift and duration while minimum gives the the opposite with a risk of burnt exhaust valve seats but in reality it's much more critical in highly tuned race engines. JMO
Many thanks, Pegscraper, I’d never visualised it quite like that before, re the length of time that the valve is open, etc. Truly appreciate you taking the time.
The major stress/load on any combustion engine is on the valve train at idle or low rpm mainly due to the spring pressure keeping the valves closed so its no wonder the seats get hammered.
