Kostas1,

You are confusing pistons which have rings and bearings which support the crankshaft. Pistons come in ringed or non-ringed engines. Non-ringed engines have a tapered bore that gets smaller toward the top (refered to as the pinch). Ringed engines are not tapered and rely on the ring for compression.

Now plain versus bearing engines. Actually both are forms of bearings. A plain engine has a sleeve made of some softer material like brass. The crankshaft fits inside the sleeve and relies on the oil in the fuel to provide a lubrication layer between the crankshaft and the sleeve. A very effective and inexpensive method of providing bearing support. The sleeve is referred to as a bushing.

The other bearings are ball bearings used to support the crankshaft. There is a small bearing up front and a large bearing inside the front face of the crankcase. If you remove the coverplate in the back of the engine you can see the large ball bearing. The balls ride in a race, there is an outer race and an inner race. The same is true of the smaller bearing up front. The inner race supports the crankshaft and the outer race mates the crankcase.

Ball bearing engines are a little bit heavier than their cousins with bushings. Both are reliable and prefrom well. Ball bearings can be replaced and often suffer from rust, the bushed engines are not rebushed (it can be done but is very expensive compared to replacing ball bearings).

Many think that ball bearing engines have less friction due to the use of the ball bearings and thus rev up to higher RPMs. There may be some advantage there but the real advantage is being able to replace the ball bearings pretty easy. I have never heard of anyone replacing a bushing though I guess it is possible.

Ball bearing engines cost more, usually referred to as the "Pro" series in Thunder Tiger and Magnum 2 cycle engines. Almost all four cycle engines have ball bearings due to higher impact forces of the compression and firing implues.

Thus all OS LA engines are sleeve or bushing engines, all the OS FX series are ball bearing engines. Note the cost difference.

Cheers,

Chip