Alan

I believe that valve overlap is still taught within the first 2 years of tech college training courses (According to the apprentices log book) so I could not accept that this basic information would not be known.
I fully accept that forums are often difficult places for posts to reflect all the thought processes and things do get misunderstood or are interpreted differently by everyone that reads them. It is also easy when you “know” to forget that not everybody does but this was such fundamental knowledge for any technician that I found it surprising. I don’t really want to call anyone’s professionalism into question directly without actually knowing the person but the thread speaks for itself.
I guess that the OP maybe someone much younger than I am and may not have had to set 1000's of tappets over the years and this may just about explain the term not being recognised, although a simple Google search brings up numerous pages that could be used for self learning.

Steve