Re: What causes the OHV's to go out of gap ?
Couple of random thoughts here.
Assume this is an OHV engine and requires adjustment much more frequently than the manual recommendations, poor fitting adjusting nuts or jam nuts or the studs might be working loose. Depending on engine, studs may be pressed in or threaded.
You might try putting a mark on the nut/stud after the next time you adjust. After a time, if the valves go out of adjustment again, check to see if the marks are misaligned, indicating the adjusting nut is loosing grip and allowing it to back off. At the base of the stud where it enters the head casting, you might try the same thing. Mark it with a scratched line. A pressed in stud will be harder to detect, and may require a depth gauge to compare before and after stud to casting height. A screwed in stud will show the misaligned marks if it is working loose from the head casting.
Check all contact surfaces too. Improperly heat treated valve tips or other contact points can wear.
Not sure if overheating can impact valve adjustment, maybe someone with more experience with overheating can comment.
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