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Repair or replace?

Yes, over the damaged end to keep it all together. Drill the collar where the cross pin protrudes, or grind the pin flush .
 
When assessing risk, I like to try to put things in terms I can relate to.
10 inch diameter sheave spinning at 1750 RPM means the outer edge of your sheave is doing about 50 mph. If it's 3600 RPM, it's about 100 mph.

I've been hit in the forehead by a bee while doing 60 mph on a motorbike. Sure glad it wasn't a few ounces of steel.

I'm trying to understand what would have caused those cracks in the first place. My guess is this is not steel, it's cast iron (maybe nodular iron), and I'm guessing it was pressed on. Does it run true, or does it wobble?

Failure would likely mean one of the small chunks flies off from adjacent to the shaft (where the visible cracks are). Their velocity would be much less, so that's good. But, what the rest of the sheave does after the hub comes apart is anybody's guess.

This has a skookum belt guard around it, right?
 
Elektrishun said:
I found hairline crack on the main pulley driven directly by the motor:
Click to expand...

My very first question on reading this was: What caused the cracks to happen?

The pulley is cast iron no?

This tapered pin is...... ?

If it is tapered, is the fattest diameter of the pin bigger than the hole? Could it have been tightened enough to initiate cracking?

I don't think all these radial cracks suggest overloading of the pulley shaft or relative movement between the pulley and shaft. However, they could be formed by overtightening the tapered pin.

I think the reason for a tapered pin is to take up all the clearance in the hole so that the pulley cannot move relative to the drive shaft. Likely, the first design was a straight pin. That was changed to a tapered pin when the hole started to wear from relative movement of the pulley and shaft.

But I'd bet there was a tightening spec on that pin. Either for driving or torque.

I think those cracks are from overtightening the pin - either driving it or torquing it.

I'd favour an exact fit shear pin over a tapered pin.

I also like @Darren's collar idea. But when you make the collar keep in mind that these cracks are likely caused by the pin not by the shaft load. So the collar should be installed and tightened before the pin.

I don't think brazing or welding will help. The expansion caused by the pin must be dealt with or it will just crack elsewhere.

Do you have an owners or Service Manual for that machine? If so, look up that pin and the install procedure.

I could also be all wet. But those are my thoughts on it without the benefit of being there.
 
FatherWes said:
When assessing risk, I like to try to put things in terms I can relate to.
10 inch diameter sheave spinning at 1750 RPM means the outer edge of your sheave is doing about 50 mph. If it's 3600 RPM, it's about 100 mph.

I've been hit in the forehead by a bee while doing 60 mph on a motorbike. Sure glad it wasn't a few ounces of steel.

I'm trying to understand what would have caused those cracks in the first place. My guess is this is not steel, it's cast iron (maybe nodular iron), and I'm guessing it was pressed on. Does it run true, or does it wobble?

Failure would likely mean one of the small chunks flies off from adjacent to the shaft (where the visible cracks are). Their velocity would be much less, so that's good. But, what the rest of the sheave does after the hub comes apart is anybody's guess.

This has a skookum belt guard around it, right?
Click to expand...
IMG_20241030_173228.jpg
IMG_20240104_202305.jpg

Guard is on left of first picture.
You can kinda see it in place in the second picture (back left corner).
 
Susquatch said:
My very first question on reading this was: What caused the cracks to happen?

The pulley is cast iron no?

This tapered pin is...... ?

If it is tapered, is the fattest diameter of the pin bigger than the hole? Could it have been tightened enough to initiate cracking?

I don't think all these radial cracks suggest overloading of the pulley shaft or relative movement between the pulley and shaft. However, they could be formed by overtightening the tapered pin.

I think the reason for a tapered pin is to take up all the clearance in the hole so that the pulley cannot move relative to the drive shaft. Likely, the first design was a straight pin. That was changed to a tapered pin when the hole started to wear from relative movement of the pulley and shaft.

But I'd bet there was a tightening spec on that pin. Either for driving or torque.

I think those cracks are from overtightening the pin - either driving it or torquing it.

I'd favour an exact fit shear pin over a tapered pin.

I also like @Darren's collar idea. But when you make the collar keep in mind that these cracks are likely caused by the pin not by the shaft load. So the collar should be installed and tightened before the pin.

I don't think brazing or welding will help. The expansion caused by the pin must be dealt with or it will just crack elsewhere.

Do you have an owners or Service Manual for that machine? If so, look up that pin and the install procedure.

I could also be all wet. But those are my thoughts on it without the benefit of being there.
Click to expand...
I found some basic information but nothing too detailed about the tapered pin. Knock it out and put it back in is essentially all of the instruction.
 
If the crack is there, then there must be some load on the metal. Unless it was dropped on the floor or hit with a hammer, that load comes from the pin somehow. The idea that the pin has simply been overtightened makes a lot of sense.

I wouldn't be too concerned about it for 2 reasons. First there is a lot of metal and the force from the regular shaft load can't really act on the cracked section. For it to fully fail, the pin would have to pop out a wedge shaped section and there should be a bearing that makes that difficult.

Second if it does fail, you expect a loss of power and not much else. Even if the guard is off, the fragments won't a ton of energy and it would be a fluke if they hit anything. Something like large chips

I also agree that a roll pin is a much better choice. and if you are worried about it, drill a new hole. The part probably has a lot of life left if this is the only damage
 
Tom O said:
I wouldn’t worry too much about it, the tapered pin still goes through the shaft and the other side of the collar so it shouldn’t give a problem, if I was worried about it I’d cut a groove down the crack and braze it. Or even easyer drill another hole 90 deg to it and use a taper reamer to size for the pin.
Click to expand...
And don't drive the tapered pin out from the wrong side and crack it.:oops:
 
Susquatch said:
^This.

Which might also totally explain what happened in the first place!!!!
Click to expand...
I was thinking about it and the pin came out rather easy. It is definitely tapered and will only go back together one way. Therefore, I don't think I was the culprit. Maybe someone before me made that mistake.
 
You could mill that end off down to the last crack and start a new roll pin hole 90 degrees to the first. That way there is no further chance of crack propagation.
 
I like the shaft collar idea. It reminds of what an old gray hair told me many decades ago: "Just do it right. You'll sleep better." It's likely the "do nothing" approach would be just fine.
But...
 
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