Jetpack, Ed and Hobbsy...

I think it was when Carlsen or MECOA were first bringing in AME engines - the half-A's - that I saw a recommendation in the instructions to pull backplate (and head if a glow) to soak the opened engine several hours in 'white gasoline' before attempting to operate the beast. (I may have seen similar recommendation with one or two other Russian or mainland-Chinese-engines.) Then: clean, wipe dry, oil and reassemble. I've done this with several engines, particularly from those parts of the world, since, and invariably found some dissolved gunge soaked from the exposed innards. Subsequent running-in went pretty much as described in the manual - without problem, unless the engine had something else specific "off".

(To JP particularly) having the headbolts tight is not always enough. If they are socked home the way I heard had been done as a matter of course at one mfr's factory, it's worth going through the alternating triangular sequence I mentioned above. That one company had powered Phillips head tools on extension drives overhead, and the relatively low-skill line installers just went around the bolts in sequence, once. Not alternating. Just 12-2-4-6-8-10 (o'clock) and done! I don't even like the shape of Pringles in potato chips...

Further, some factories do initial bench runs before boxing up the units for shipping and sale. PAW and FOX, I believe, for sure. PAW claims an engine is not sold unless it meets the factory benchmark RPM. I haven't found swarf or crumbs inside either make's new engines, but a bench run may have blown such stuff through and away. No serious apparent damage ever conclusively noted...