Suitable Sheer Bolts

[RickB]

Thanks all. As I say the PTO shaft isn't particular to that snowblower, it's just a standard shaft that the previous owner used. However looking at a generic parts place, if I selected a PTO shaft to suit my tractor's output, it's right enough that it would have an 8mm shear bolt. I have some concern about the bolt rating. I still think I might just try it with 8.8 (your Grade 5), it's not a big deal changing it if that's too weak.

For the augur the manufacturer's diagram and parts list just describes it as "M6 x 30 bolt". I don't think it's ever been changed as it was still painted over when I removed it to grease up the joint. Again all I think I can do is try some standard bolts. That one's a bit more fiddly to get at, but not as bad as on our walk behind.

I understood what you said about the generic PTO shaft. That’s why my response references the OEM shearbolt spec for your machine.

 

[aesmith]

I do not have a clear understanding of the location of the shear bolt for the augur. Is it between the shaft and the drive sprocket or between the driven sprocket and the end of the auger shaft?

It's on the driving side of the chain, between gearbox and drive sprocket.

 

[aesmith]

I do not have a clear understanding of the location of the shear bolt for the augur. Is it between the shaft and the drive sprocket or between the driven sprocket and the end of the auger shaft?

It's on the driving side of the chain, between gearbox and drive sprocket. If this picture works, part 42 is a 6mm bolt, and looks like a deliberate weak link. It's only fiddly because it's screened from access except from the underneath. By comparison the augur shaft connects to the driven sprocket by four 10mm bolts.

 

[Captain Dirty]

It's on the driving side of the chain, between gearbox and drive sprocket. . . . It's only fiddly because it's screened from access except from the underneath. By comparison the augur shaft connects to the driven sprocket by four 10mm bolts.

Got it. My suggestion in comment #8 is moot.
If, after a season or two of use, you find replacement of that shear bolt is a frequent nuisance, you may be able to make a hinged or easily removed access panel in the plates that screen the top without compromising the bracing such plates might provide.

 

[PILOON]

I agree with LouNY.
Soft will stretch B4 shearing and become a bugger to drive out and also will tend to damage the holes they occupy.

Grade 5 still protects nicely but will shear clean.
Nothing is worst then trying to drive out a distorted shear bolt barehanded at -25 or -30 degrees.


Harder to determine is weather the shear bolt is metric or SAE as you really want a snug fit.
Think of the shear system like a pair of scissors, the cutting edges need to be sharp to be effective and sloppy fits create dull cutting edges.

 

[mykleh]

one thing to keep in mind in the aesmith diagram I didn't when I had my 3pt was taking the bolt out at beginning of season and make sure plates hadn't rusted together.. I blew up my PTO coupler and I was WTH till I realized it wasn't the grade 5 1/4" bolt that was the problem the two plates sandwiched together had rusted and it wasn't relying on the bolt as a shear point anymore..

 

[aesmith]

Thanks for the comments, looking at regular agri parts places it seems like M8 PTO shear bolts are normally 8.8 (Grade 5), and 10mm are offered in 8.8 or10.9. Also thinking about it I'm less concerned about the PTO as whatever sort of 6mm bolt or pin I fit to the augur drive is obviously going to break first. I'd have to be very unlucky to get something into the impeller that didn't block the augur on the way in.

The point about the flanges is well made, I've checked and greased them when checking the blower over just now.