Oops

[cheeseheadmike]

I've been slowly working on my 90 year old Craftsman 918. I just finished up with re shimming the main shaft babbitt bearings and replaced all but the drive belt. I was running it while checking the bearing caps with a laser thermometer when it started shaking. Before I could turn it off, something came flying out at me, and all the shaking stopped. It was running smoothly and almost silent.
What came flying out was the outside half of the drive pulley.

I don't know if the belt was too tight, the pulleys were out of line, or if the pulley was bad to start with. Any who, I bought a new pulley today and will pay close attention to tightness and alignment when I install it.

 

[OTmachine]

From what I can see in your picture, it looks like a fresh fracture, with the pulley being the weak point.

 

[Provincial]

Die cast pulleys are not very stout. I am of the opinion that die cast parts weaken with age. This is not an uncommon occurrence with die cast pulleys.

 

[cheeseheadmike]

Die cast pulleys are not very stout. I am of the opinion that die cast parts weaken with age. This is not an uncommon occurrence with die cast pulleys.

I was hoping to find a steel or cast iron pulley locally but no such luck. So I ended up with what I could get.

As nothing is ever easy, the threads for the set screw in the new pulley only went about halfway through. Fixed that, then noticed that something wasn't right with the Driven pulley. It's not the correct pulley, and it looks like someone tried to make it fit by using a Dremel in the bore. I cleaned up the bore with a reamer and now it fits like it should. I got the pulleys lined up and put a bit slack in the belt. Everything seems happier now.

 

[markba633csi]

It may be "zinc pest", a disease that affects zinc alloys when they haven't been made to a certain degree of purity

 

[Jake M]

Die cast pulleys aren't that stout, but you didn't do that in one shot with a drive belt. You may or may not have adjusted the tension with a four foot snipe, but that's not what they look like when they get "that" overtightned. Maybe a crack was growing, maybe the (normally) thin spot was worn down thinner from past use with a loose or worn belt? I dunno. I wouldn't get scared and "under tighten" the new one, just the same proper snug as any other belt that size, and move on...
Those new Chicago die cast pulleys are not that bad. They're not industrial, but plenty good. You'll never have to touch that one again if you don't want to.