Talking about the rated rpm for piston pin bearings is meaningless. They oscillate! This means a very different strain. Therefore, these bearings have to be different from normal needle bearings. Here extremely strong dimensioned and hardened steel cages are required.
(Click twice to enlarge)
Different bearings from the left:
Original INA KZK 16x22x12; Stage6 No. S6-802002/XL which is 10x14x15; original INA KBK 10x14x13; China HT bearing of my 48cc engine.
Here is the piston pin bearings with more details:
This must be avoided at all costs here. The needle must not look out from the connecting rod:
This failure occurs because the piston bosses are to far from each other. One notices that the piston was designed in the time of bronze bushings. This design should have been changed for needle bearings. But they didn't.
The most important step to get the rod in the center of the piston: The crankshaft must be mounted at its center. It must not move during operation. My had about 1,5mm axial play. I suggest 0.3 mm axial play which should be set with the fitting hardened washers betweeen each crank and its 6202. When that is done, the play between the bosses should be reduced to about 0,5mm at each side.
My goal is a long lasting HT Engine - Multipaul