BMW 326rb build thread...

[ctnewman]

Originally Posted by Def

I guarantee you the temperature the crank/oil gears run at doesn't reduce their strength any measurable amount. If you're shearing things off a rotating assembly after some period of time, it is 99.999999% of the time a vibrations problem. The load of spinning the oil pump isn't that much, the load of an assembly vibrating around against another piece can spike quite high and cause fretting and eventually fatigue failure.

I disagree. Loading the drive gear off-center AND partially is a huge stress riser.

Inline 6 cylinders are very well balanced.

[Def]

Originally Posted by ctnewman

I disagree. Loading the drive gear off-center AND partially is a huge stress riser.

Inline 6 cylinders are very well balanced.

Balance has nothing to do with torsional vibrations. You are speaking of external vibrations anyway, which is not what I'm talking about.

The crank twists back and forth like a tuning fork vibrates, which is why the factory puts on a harmonic damper(i.e. the crank pulley).

Let me put it this way, you externally spin the engine to 8000 RPM and the oil pump gears won't feel much load at all. You start running the engine and the torsional vibrations in the crank will rise and fall according to the 2nd order mechanical response of the engine's rotating assembly. This vibration GREATLY loads things.

Yes, the structural design of the gear probably isn't ideal, but the reason why it is failing is because it can't put up with the stresses it experiences due to torsional vibrations. It's probably easier to calm TVs on the crank than to make things strong enough to deal with an unfavorable vibrations environment.