Snow Attachments Shear Pin Question

[hiker88]

These are threaded all the way. Maybe I will try a grade 5 and see how it goes. I still plan on engaging the PTO at low rpm, but with these you don't get a second chance if you forget.

The blower is used so I don't have any documentation. Is there an OEM bolt I can buy?

 

[Woody65]

These are threaded all the way. Maybe I will try a grade 5 and see how it goes. I still plan on engaging the PTO at low rpm, but with these you don't get a second chance if you forget.

The blower is used so I don't have any documentation. Is there an OEM bolt I can buy?

The bolts should be smooth the length of the shaft that it is going through. The threaded part of the bolt should not contact the shaft if it is the correct size. It sounds like you have bolts and not shear pins. As stated before, you can use them but they are not as reliable as the correctly sized shear pins. I have, in a pinch, used regular bolts to get me through the project.

 

[JerryK]

If you Google MK Martin and shear bolts you might get lucky. First pdf file I got listed a 6 X 40 metric shear bolt/nut assy, but don't know if that was your blower. Amazon and Ebay is a source for pins, but they are pricey.... You have to figure out what you are looking for size wize, then try to find something that fits. Unless, you have a source for MK Martin parts. Anyother thing you can do, is buy a bolt with a shoulder the lenght you need, then cut off the threads long enough for the nut. Trick is to put a nut on the thread before you cut them so the taking the nut off will clean up where you messed up the threads cutting it. This isn't that hard, just a pain in the arse.... Good luck, Jerry

 

[kco]

These are threaded all the way. Maybe I will try a grade 5 and see how it goes. I still plan on engaging the PTO at low rpm, but with these you don't get a second chance if you forget.

The blower is used so I don't have any documentation. Is there an OEM bolt I can buy?

The manufacturer is MK Martin. I called them once and they were very helpful. You can download free manuals for their blowers here:

MK Martin | Support

I see a copy for the 54 & 60" model that may apply to your blower. I did not attach it since it is 4 MB in size.

If your blower and PTO assembly (a Comer T20, made in Italy) are the same it appears you need a metric 6mm x 40 mm grade 10.9 bolt (item 71 on page 21). I believe metric 10.9 and 8.8 roughly relate to SAE grades 8 and 5. So the 6mm, 10.9 would be close(.24") to a 1/4" grade 8.

 

[chim]

Does the PTO shaft telescope freely? If it doesn't I suppose it could put some extra stress on the pin.

 

[hiker88]

Thanks, that does appear to be my unit. So I have been using a grade 2 bolt, with the threads in shear so I can see why it went so easily. I will check around and get something more appropriate. I read the docs and it advises to bring the blower up to speed after it is engaged so I will continue operating it that way as opposed to engaging it at higher RPMs.

Thanks again everyone.

 

[HillStreet]

I have a SB 51 by Meteor and here is the manufacturer spec on the shear bolts:

PTO shear bolt is M8 x 50 - 8.8
Auger shear bolt is 1/4 x 1 grade 2

My blower is 3 years old and only sheared the auger bolt once-- wound up a tarp that was buried in the snow.

Also broke the PTO bolts twice, caused by lifting the 3PH too high and stretching it to failure. I do usually engage PTO at low rpm.

 

[joeyd]

This is a copy of the email I received from MK Martin when I questioned them about shear bolts for my MK68.

Shear bolt are standard fasteners, for auger drive should be gr2, and shear bolt in pto is metric gr8.8 (metric bolts are graded different, gr8.8 is comparable to gr5)

 

[SPYDERLK]

OK. No hash marks on these bolts - just SJ 3074. I think I should get some grade 5s. Hope it snows again soon - it was a lot of fun except for replacing the bolts.

Thanks for the responses. I will try to sum up my answers. When I say shear pin - it's actually a threaded bolt marked SJ 3074 - don't know if that makes a difference. The bolt hole where this goes is a nice snug fit, there is no slop in the hole.

Here is what seemed to work last night: I got into a practice of pulling up about half a foot or so of where I wanted to move snow, drop the blower to the ground, put the shuttle in reverse, downshift the transmission to 1st (I stayed in low range all night) and then I would ease out the clutch and start backing up. As soon as I start moving, I would step on the foot throttle and bring it up to the red triangle on my tacometer.

One of the times I broke a shear bolt I think it was from lifting the blower to the top of the 3 point travel. In retrospect, I think I must have compressed the travel in the blower drive shaft too much and it snapped the bolt in that instance too. The PTO was engaged at that time.

These must be shear bolts because they snap clean as anything. I would find one half sitting on top of the hitch area right below the pto and the other half would be in the collar and I could pluck it right out. Both side had a near perfectly flat surface to them with no bending.

I wonder if the bolts I have are not grade 5?

Yes, Gr5 will be good. You should also assure that the PTO shaft does not compress fully at any point in lift or any condition of use.
larry

 

[smfcpacfp]

Why not simply buy the bolts suggested by the manufacturer rather than getting a variety of answers from people on this forum?

I always engage my blower at idle and then increase the RPM's as someone else mentioned.