Your summary re the problem is close enough, but there was a fatal detail which caught me out 100%.
THE TOP CRANK CAP HOLES ARE NOT BLIND. THEY ARE CONNECTED TO THE OIL GALLEYS*.
After the blasting, the cases were meticulously cleaned internally, and well enough (he thought ...) externally.
I never paid enough attention to these two holes, ASSUMING they were blind as many external holes are.
In my case they further 'seemed' blind as they their bottom was filled with sealant which resisted my air and water guns.
At the time I stupidly, missed the hint offered by Honda putting an o-ring around these screws, clearly shown in the parts catalogues ... but there you are
Had I realised this little-known fact, maybe the problem would not have happened. Regardless, I do agree glass blasting cases or even complete engines is a stupid idea, which however is quite common in the UK!!
I have now cleaned and re cleaned theses holes. However, when time comes to prime my newly rebuilt engine, I will leave the two crank caps out for a minute or so to get new oil pumped out of these two holes, further cleaning them, in case anything is left in them (which I doubt).
In any case and under normal servicing, these holes can get very dirty. Also I know of many people who drill and helicoil these as they are quite prone to stripping.
Chaps, beware of what ever is there after a long service life, or you inadvertently put there e.g. after helicoiling, as they are not as innocent as they look!
Best, Aris
*From data I have gathered in the last few months by asking around, in some engines these holes are blind, is some partially open, and in my case, the one on the left quite open (and hence the problem with rods 1 & 2) and on the right almost closed hence my no 6 rod staying healthy
.
), and only then fire the engine.
, sitting again onto the bike lift with carbs installed.