RE: Old Soviet Union 10cc engine
Well, that is what the instructions are showing. Yes it does appear to be ABC on the inside. But yes I can agree those are odd instructions for a ABC type of engine.
Of course they might have recycled a instruction booklet from a older ringed engine at the time.
The 4 hour engine longevity statements are interesting. I think the thought that it was to avoid warranty issues was probably the best reason for it.
I don't know if anyone tried to make or run a .60 size engine with a mehanite piston in it. How much vibration one gets would be interesting.