I could tell that the bearing(s) where bad just by feel. It still ran fine. A sign that you have a bearing going bad is a flameout with a crushed glow plug element. A piece of the cage has gone thru the motor and killed the plug. This is why phenolic cage bearings are better, but more costly. If you have a bearing really go bad, the crank will run off center, and destroy its tight fit in the crankcase. This tight fit acts a a seal, now your motor will blow fuel from the front bearing. I plan on building an OS 70 (?) from SF, and SFN parts. I will use a longstroke SF crank and rod, with a short stroke SFN ABN piston/liner. The hardest part will be making a thick head gasket shim. The short stroke head extends farther down the liner than the long stroke. I think it will have a bore and stroke of 24 mm x 24 mm, I would have to check the specs. Not really sure of what the displacemant will be, just guessing.

Alan