Snow Shear bolt question

[SylvainG]

As I wait the arrival of my new 68" MK Martin Meteor snow blower, I have a question regarding its auger shear bolt. Not knowing if it comes with spares, I want to be prepared. According to the manual, the shearbolt (#16 in the following image) is bolted between the two metal plates, one attached to the sprocket (#17) and the other attached to the auger shaft (#15)



Now, since snow blower shear bolts usually have two groves where the auger and shaft meets to 'give' when too much force is applied to the auger, in the Meteor's case. these are useless, right? Would a standard 1/4" x 1-1/4" grade 2 bolt and nut would suffice? The manual mentions "Shearbolt 1/4x1 1/4 #2" but I have a **** of a time to find these. All I find are 1/4" x 1-7/16", 1/4" x 1-1/2" or 1/4" x 1-3/4", not 1/4" x 1-1/14".

 

[airbiscuit]

Any hardware store should have 1 1/4" bolts. They are listed on the Menards site. https://www.menards.com/main/tools-hardware/fasteners-fastener-accessories/bolts/cap-screws-hex-bolts/grip-fast-reg-1-4-20-x-1-1-4-galvanized-steel-grade-2-hex-bolt-8-count/g2hb14114-8sb/p-1508335479674-c-8730.htm?tid=-6948719105361415712&ipos=6
In any case, what difference would it make if it was slightly longer?

 

[oosik]

Check for the recommended length at a different hardware store OR buy on line OR 1/4 by 1 1/2 with proper number of plain old washers to take up the added 1/4" length.

If grade 2 is recommended - don't go to grade 5.

 

[mikester]

I use 5/16x2" grade 2 fully threaded black (un-plated) carriage bolts because I have a big box full of them. I also keep some spares with double nuts in the tractor tool box. Length doesn't really matter as long as you can put them in and no interference anywhere. I usually end up breaking 1 or two a season...easy enough to fix on the spot.

 

[SylvainG]

Thanks for the replies. I was looking at a video of someone with the exact same blower where he sheared the bolt by hitting a log. I think anything longer might be harder to slip in. I guess I could put it the other way but I think it would then be harder to screw in the nut (just by feel, not seeing it, specially with frozen hands ).

Here's the video where he tries (and fails) to get the bolt in

Hitting Firewood Pile with Tractor Snowblower - YouTube

So from what you're saying, any grade 2 1/4" bolt should do. It doesn't have to be a shear bolt with those two groves in them, right?

Thanks again

 

[jaydee325]

The owners manual is on Martin Meteor website. It specifies a "Shearbolt 1/4x1 1/4 #2". The parts list also specifies to obtain locally, so it's nothing special.

 

[SylvainG]

Yeah, I have the manual. That's where I got that clip from. Looking locally, I can only see snowblower shearbolt in a size longer than 1-1/4" hence why I asked if any type of grade 2 bolts would work since by the design of the safety shear method used by that blower, it's not going to shear at those groves anyway.

 

[rScotty]

Yeah, I have the manual. That's where I got that clip from. Looking locally, I can only see snowblower shearbolt in a size longer than 1-1/4" hence why I asked if any type of grade 2 bolts would work since by the design of the safety shear method used by that blower, it's not going to shear at those groves anyway.

I can see why someone might put grooves in a shear bolt for some special application, but like you are saying that means the grooves have to be at the right place. That's a hassle, so generally shear bolts are just standard bolts - often #2 - that are located where calculations show that too much torque on the blower shaft will cause them to shear.

In the shear bolt design you've pictured, the designer can vary the shearing force by changing the distance to the shear bolt hole .... which is a positive. The downside to doing it that way is that the shear bolt's clamping force and the friction between the metal plates are now also part of the shearing calculation - which are extra complications you hope that the designer was aware of. You'll want to keep an eye on that bolt to make sure it shears.

If you are driving the blower mechanically with a a tractor PTO, I'd also check that the tractor PTO output shaft has some protection. Most do, but not all. So check it and consider adding a standard friction clutch to the setup to protect the PTO if it doesn't have one already.
Doing that is not as much a concern if you are driving the rotor hydraulically.
Have fun out there,
rScotty

 

[SylvainG]

Yeah, I read a thread where someone said his Meteor blower is eating shearbolts for breakfast until he tighten it against the shear plates. Like you said, too much friction there would be counterproductive. I guess I'll have to see with times the best torque required.

Yes, the PTO shaft at the fan has a 3/8" x 1-1/2" grade 5 shearbolt. That's something else I'll need to get extra. Tractor is a dual stage wet disc clutch so I guess it's mechanical.

 

[Beaver Cove Deere]

I use shouldered .312-18 grade 5 bolts. Not full thread on my Normand.