Broken intermediate shaft pulley

[peterman]

I cannot find a single instance of this happening to anyone else online. Which makes me think think theres some funky things going on inside.
Relavent specs:
Fresh rebuild
M50b28 crank
Je pistons
325i rods
Replaced the intermediate shaft bearings - spun freely but no excessive play.
Pulley is the sintered version
I havent pulled it apart yet but looking for thoughts. Has anyone seen this happen before? The only thing I can think of is that the pump locked up. I had a good 40 psi at idle.

[hasa]

Does the shaft pulley turn by hand?

[digger]

Maybe bolt came loose (insufficient preload or it wasn't seated correctly) and rattled around pounding the pin and bolt. I have seen the pins broken off before.

[peterman]

The broken bolt has a consistent 45 degree helix break associated with a torsional failure. My thought is that the pin broke, then the bolt continued to tighten because of some crazy drag or hard stop in the oil pump or pump shafts. Essentially, timing belt constantly tightening the bolt until failure.
I have not tried to spin it yet.
I am glad to hear that you have seen that failure though, digger

[digger]

The broken bolt has a consistent 45 degree helix break associated with a torsional failure. My thought is that the pin broke, then the bolt continued to tighten because of some crazy drag or hard stop in the oil pump or pump shafts. Essentially, timing belt constantly tightening the bolt until failure.
I have not tried to spin it yet.
I am glad to hear that you have seen that failure though, digger

i have seen the pin break off but as it wasnt my engine idk what the bolt looked like or the outcome

The witness marks suggest the gear spun on the end of the shaft so it was atleast loose for quite some period of time so that will likely be why the bolt failed. If the bolt came loose then this could explain why the pin sheared off.

the belt tension and resulting torque probably isnt enough to over tighten the M10 gr10.9 bolt as it acts over a fairly small radius so the gear just slips and can oscillate