So after my discussion with Eddie on the possible interference with the valve I start looking at the rockers
One is quite damaged - which is to be expected - it takes a while but eventually I notice some wear on some of the rockers.
It is actually quite hard to see unless you get the light right - I took a bunch of photos and you can only make out the wear in a few so I'm posting those.
not damaged
damaged - note the ridge where the tip roller slot ends.
a slight bevel has formed.
with the flash on you can see that almost half the rockers have formed this bevel.
I have a dual pattern cam and the intake lift is greater than the exhaust lift - so this would support the idea that the intake rockers may have been interfering with the spring cap and perhaps introducing a little side load.
Given the very slight nature of the wear it may be something that has developed recently.
A note on blame:
I feel compelled to try to cut off any criticism of the engine builder here.
I ordered the push-rods before the engine was assembled not realising that they should be specifically measured.
When I picked up the engine the push-rod length difficulty was pointed out to me and it that it was 'a lot of stuffing around to get them to clear' and that was over 8 years ago.
I could have done something about it in that time but let it go.