ball bearings--support the crankshaft. Most have them at the front and back--this is the best setup. The other alternative is a bushing--basically a polished metal to metal point of contact--much more friction using this setup than with ball bearings--therefore, the ball bearing engines aren't robbed of as much power as the bushing engines are.

ABC--aluminum, brass, copper (I think). Some are now nickel plated. This refers to the cylinder--non-ringed engines are lined with a combination of metals that allow for hardness, but also allow for expansion so that the piston just fits as it reciprocates up and down. This allows for the piston to not use a ring--compression is maintained by the tight fit between the piston and the cylinder wall.