I thought the top end issues came from no one cleaning out the oil filter because Honda screwed up royally and made accessing it a huge pain in the ass. I believe that is what puts it on bypass. I bought one that hadn't been run in 25 yrs. once that did have a wiped cam bearing surfaces, but it's filter looked like it had a couple tubes of silver solder in it.
The 'solder' came from the cam bearings after they failed,and was not the cause of failure. Normally its like dark grey cardboard in there.
Its a centrifugal filter which doesn't really need cleaning out as it just gets a smaller inside diameter after 5~10 yrs constant use.
It works best at high rpm which is when the cam bearings fail.
Oil is fed in through the center, centrifuges any heavier particles then returns to outside of feed hole ( also pretty close to center). When pressure relief opens almost all the oil sprays back into clutch cover.
The big ends and main bearings don't need much oil, and, as the big ends don't have any pressure feed, they survive very well in the oil mist. However, when the pressure drops the oil stops going up cylinder studs to lubricate cam bearings and rockers.
The points side always fails first in my experience.
Drilling out the restrictor holes in crankcase allows more oil up studs and drilling a feed hole in bearing surface also helps to lower pressure in filter while increasing lubrication to top end
. It doesn't seem to have any effect at low rpm.
I think the extra oil to top end may also have some limited effect on cooling, picking up extra heat and delivering it back to sump.
PJ
