The air cooled Volkswagen engines I ran back in the late 1960's were notorious for burning valves until I learned to run the exhaust valve clearance a couple of thousandths loose. Stovebolts don't have quite as much of a problem because they're liquid cooled, but too tight is always more likely to cause rough running and/or valve burning than adjusting the clearance a bit loose and putting up with a little tick noise.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!