Originally Posted by Creative Engineering
It's all a matter of tolerances,
An engine with a sloppy needle bearing fit will not hold up compared to an engine with a properly honed bushing.
An engine with a sloppy bushing fit will not last. An engine fitted with a precision wrist pin and needle bearing will last.
You can't blindly compare the 2, because either design can be executed improperly.
Every time the engine fires...it's a hammer on top of the piston. If there is any play in the wrist pin to rod fit, the bearing material,(no matter what it is), will get hammered until it fails.
I prefer phosphor Bronze bushings...so far all of my 2-cycles have had needle bearings. I haven't had the opportunity to do a longevity test on any of them...but my customers will!
Jim, From my 8 years of drag racing motorcycles and 23 years of MC repair and
engine rebuilds, I would only recommend a bushing for the wrist pin end. Like
you stated, "it's a hammer on top of the piston". The upper wrist pin end of
most engines has very little rotation as it travels up and down. This puts a
LOT of stress to the same area of the bushing or bearing during its limited
rotation. If one would examine a worn upper rod bushing you would see that
it always wears oblong due to the upper and lower "pounding" it takes.The
roller bearings do no not really allow rotation of the bearing rollers, which
causes early fatigue and failure of the bearings.
That's been my observation and experience from a few years of engine rebuilds.