Alternator pulley failure

[M20F-1968]

I took the plane out last weekend and was up about 20 minutes before I got a Bus Voltage Low warning on -20 amps, 11.8V.

When I got the plane on the ground I took off the top cowling and found that the belt was loose, but not broken, and the alternator pulley failed.  I cannot see the alternator part number just yet as it is behind the lower cowling and engine baffling, however, can one purchase and replace just the alternator pulley?  If I had a choice, I would prefer it to be steel rather than cast aluminum.  You can see the broken pulley in the second and third pictures.  Any thoughts or experience in this matter?

John Breda

[M20F-1968]

Pictures got rearranged - 1st and 3rd pictures show the broken pulley.  I seem to remember the alternator is a Kelley Aerospace alternator, but I may be wrong.

John Breda

[M20F-1968]

Is the pulley a weak part of the Kelly Aerospace alternator.  It would seem that this should not fail.  It looks like the Plane Power alternator uses a machined aluminum pulley.  Is this part a reason to use a different alternator?

John Breda

[N201MKTurbo]

I had a similar failure once in my M20F, the pulley didn't fail, but the fan behind it failed. My failure had much more serious consequences than yours. The piece of fan flew across the engine compartment and hit the oil cooler and made a hole in it. I was over inhospitable territory, but there was an airport nearby (Whiteriver AZ) and I landed safely. I was down to 2 Qts of oil when I landed. 

BTW, I think I have one of those pulleys in the hangar if you want to replace it.