merv
as pointed out above detonation is unlikely to be noticed in an aircraft engine. I doubt the Jab engine will detonate anyway, although given the right circumstances with low octane, hot temps etc you might be able to. But not easily.
Preignition you will likely not hear or feel much there either until you have a trashed piston.
Your description of what you found is not very diagnostic at this level so maybe none of our collective somments are of any use.
The likely issues are valve guide wear then damage to the valve as a result. High temperatures will not help either.
Complete lack of data along with so many experts having their opinion along the ay mean finding the truth is almost impossible.