[namba209]

Actually, it's the reciprocating mass that causes the problem. Think of the piston and rod combo as being a jackhammer on the crank journal. With shell bearings the impact loads are spread around the journal, whereas with a needle or roller only a very small pencil line is where the impact loads are at. Because that's all the area the needle or roller will have on the journal. So they eventually will flatten out and the bearing is destroyed along with the journal. At least that's what my instructor told us, and if you think about it, he's right. It's the ol' bed of nails trick, you can lay on a bed of nails, but try standing on just one, pointy side up and it'll go right through you. It's the old area/pressure rule, more area, less pressure. Using this same scenario, needles will work much better in a rotating mass, because of less friction from less area scrubbing on the bearing journals. You're right about this going off topic, too. Sorry Bob.