[PelotonToPodium]

My alternator belt fell off (but did not get sucked into anything ) and I quickly determined the cause to be a completely exploded deflection pulley. Looks like the part had seized with majority of internal bearings gone. Belt tensioner and belt are in good condition. What was left of the deflection pulley was covered in black gunk (probably oil?)

Any guesses on what could have caused failure? Seems like a pretty random part to just go out like that.

[Orion4]

How many miles on the pulley? I typically change the belt, the tensoner and that pulley every 50 k without issues. I'm at 178000 as of total.

[PelotonToPodium]

Originally Posted by Orion4

How many miles on the pulley? I typically change the belt, the tensoner and that pulley every 50 k without issues. I'm at 178000 as of total.

Just hit, 86k miles

[F32Fleet]

Normal. The grease dries out with age which allows the bearings inside the pulley to cook themselves.

[McGyv3r]

Yeah, you shoulda changed the pullies and belts around 50-60k miles.

I don't know if it's true or not, but I heard that the new belts don't crack when they wear out. Then just kind of stretch until the eventually snap or get forced through your front crank seal. It's cheap insurance to just change everything every 50k miles or so.

[PelotonToPodium]

Originally Posted by F32Fleet

Normal. The grease dries out with age which allows the bearings inside the pulley to cook themselves.

That makes sense. Nothing like bearings flying around in the engine bay. The bimmer gods let me live for another day.

[MTWO]

Originally Posted by McGyv3r

Yeah, you shoulda changed the pullies and belts around 50-60k miles.

I don't know if it's true or not, but I heard that the new belts don't crack when they wear out. Then just kind of stretch until the eventually snap or get forced through your front crank seal. It's cheap insurance to just change everything every 50k miles or so.

Ouch.