Shear Bolts

[msb1766]

Broke the impeller shear bolt on my front mount snowblower, The manual says to use grade 2 bolts on the impeller and auger connections.
There are two bolts on the impeller one that goes through the shaft and another that connects the impeller to the shaft via and ear.
The parts list says the bolt that goes through the shaft (the one that broke) should be grade 8.
The bolt that connects the impeller via the ear did not break.
The shear bolt that broke is part #62 the ear is part #51 the ear shear bolt is part #8
This is the first shear bolt that I have ever broke on the blower.
Should the grade 8 break before the grade 2?

 

[Peter 315]

Grade 2 bolt should break first , If it was all rusted together the two ears with the grade 2 bolt, might have caused the grade 8 bolt to break

 

[PILOON]

If bolt # 62 broke it is because the key # 25 is missing.

#62 is simply to retain the fore/aft positioning while the key #25 does all the work/takes the strain.

While it is possible for the key to wiggle out it would be rare.
Probably never installed at factory.

That key will be simple 1/4 X 1/4 standard key stock available usually in 10 or 12 inch lengths for a lot less than the dealer will cost you for a short part #.
Auto parts should carry that or often bigger old fashioned hardware stores.

LOL, a friend actually purchased couple of dozen of those as he would break about every 15 mins until I showed him that the key was missing.

Lucky, your 'fix' is an easy one.

 

[msb1766]

The two pieces might have been rusted together, I could only see the impeller side not the other side of the ear.
I thought about the also but the key must be there as I think it is in the gear box on the back.
Part #8 (grade 2 shear bolt) had a little bend to it but it still came out easy, I can not tell what grade bolt it is due to wear on the head.
Should I put in a new bolt there? I got some from that have no marking on them, so I am assuming they are grade 2.

 

[Peter 315]

Put in a new grade 2 bolt in part #8 no marks are grade 2, Might want to put never seize where the 2 shafts meet

 

[msb1766]

I think I will put a new grade 2 bolt in there to be safe, never know what bolt they put in at the factory, I like the anti-seize idea thanks.

 

[finn1]

I don’t know who made the snowblower attachment, but I would question the design if they are relying on a key way to transmit load. A clamped joint, or press fit would be good design practice, but a key will always have clearance, ie slop, and will wallow out and eventually fail.

Keys are used for indexing and alignment in a design. Using a key to transmit load is bad design practice.

 

[PILOON]

I don’t know who made the snowblower attachment, but I would question the design if they are relying on a key way to transmit load. A clamped joint, or press fit would be good design practice, but a key will always have clearance, ie slop, and will wallow out and eventually fail.

Keys are used for indexing and alignment in a design. Using a key to transmit load is bad design practice.

Sorry to disagree but most tractor snowblowers use that method.
My 60" Bervac.
Friends 60" Kubota uses 1/4" key to attach his PTO shaft to the blower.
Lots of pulleys have key way slots as do many electric motors.
Most gas engine flywheels are tapered but also have slots.

 

[yanmars]

If a grade 2 is required it would not be good to substitute the stronger grade 8. The cheap soft shear bolt is supposed to break before more expensive parts do. Just my thoughts.

 

[msb1766]

Pulled out part #8 (grade 2 shear bolt) and took a wire wheel to the head to see what grade it is and it is a grade 5. has 3 dashes on it.
Manufactuer or dealer put in the wrong grade of bolt.
Took it all apart, coated everything in anti-seize and put in a grade 8 bolt (part #62) like the part list says and put in a grade 2 bolt (part #8) like the parts list and diagram says to.