Snow Attachments Shear Pin Question

[hiker88]

So I went out last night to practice replacing shear pins - I mean I went out to clear the driveway.

I'm a first time tractor owner and I bought a used Meteor 60 inch snow blower to use with my Kioti CK30. We got about 5 inches of heavy wet snow yesterday, so I went out last night to give things a try.

I went through a bunch of shear pins right at the PTO connector until I figured out the bolts were snapping when I let the clutch out at anything but idle power. So, if I reduced the power to idle, released the clutch, and then brought the throttle up to 2500 rpm I would be fine. At anything other than idle, the bolts would shear no matter how I released the clutch, and I was trying to be pretty careful without slipping the clutch excessively.

The person I got the blower from gave me a shear pin, so I just went out and bought more of the same. It's marked SJ 3074 and it fits an 11mm wrench.

So, I am just wondering if that is normal operation (having to be at idle when releasing the clutch) or if maybe the shear bolts aren't strong enough. The guy I bought the blower from was using the blower on a 20 hp hydro, and he said it was a bit too big for his tractor, so maybe he wouldn't have had the issues I'm having.

Once I figured out this "work around" it sure beat the walk behind blower I've been using the last 7-8 years. Even with the heavy wet snow, the volume of snow this setup was moving was amazing, I just put the tractor in 1 low and it was awesome. It was great doing the snow bank at the end of the driveway the plow guy leaves. My driveway goes up hill to the road and the walk behind would always ride up over the snow. The weight of the meteor just kept it right on the ground.

If I can figure out the shear bolt issue - bring on the snow! Thanks everyone.

 

[kevin37b]

Make sure those shear bolts fit tight in the holes , as in a light tap with a hammer . Slop in the holes will slam the bolt when you engage . And no , stronger is not always better . What kind of angle do you have on the shaft when you engage . Set it down when you engage , sounds like it works good on the ground. Can you pick it all the way up with it running ?

 

[PILOON]

Soft ungraded bolts will stretch and tear B4 sheering and eventually cause holes to get oval which in turn will make sheer bolts sheer rapidly.
You want a neat round hole for best action and I like a grade 5 bolt for nice clean cuts.
My 2 cents.

In fact if a 1/4 hole is messed up and sheering frequently the best option might be to ream out to 5/16 as I did without adverse results.
(still sheer more than I'd like. LOL )
Even chunks of hard ice can cause a sheer.

 

[JerryK]

As to your question about having tractor near idle when engaging the PTO... that's the way you should always do it if possible. Idle down, and be easy on the clutch when you engage. If it is a hyd PTO type clutch, it should have an accumulator on it to take some of the shock load when the PTO engages. You can go to higher grade bolts, but then you take more of a chance of destroying your blower gear box, putting extra stress on your PTO shaft joints, and possibly bending the blades on your impellor fan. [ Sadly, I know the latter from experience... ]

 

[hiker88]

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?

 

[JerryK]

The shear bolt assy in the pto shaft has a little slop in it. When you lift the blower all the way up it puts a lot of strain on this shear bolt area and actually trys to pull the shear bolt longer. That can break them, and at least streach them so they are not tight anymore. The low grade shear bolts will strech some and it is almost impossible to keep them tight. If you go to a higher grade, they don't stretch as much, just snap... but you want the low grade easy to break shear bolts. If you can, try to find some bolts that are of resonable lenght, but do not have threads in the area that usually breaks. The threads make the the shear bolt area weaker, but also chew up the steel they are bolted to. That's what adds to the elongating of the bolt holes... Most orginal shear bolts have long unthreaded areas and are Grade 3. Grade 5 bolt heads have three hash marks on them...

 

[Woody65]

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?

The top of the bolts have markings on them to denote the grade of the bolt.
No markings = grade 2
3 hash marks = grade 5
6 hash marks = grade 8
If you don't know, the higher the grade the harder the steel. I always try to engage the PTO at idle with any implement. Less stress on all components.

 

[hiker88]

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.

 

[JerryK]

Also, a new blower is tighter than an old loosy goosy unit... and that tends to make the shear bolts fail early. Once you get the op trained and the blower run in... you should be not hardly ever changing the shear bolts. Unless you find some big rocks, ice blocks, neighbors lost chain, etc....

 

[JerryK]

Sorry, the bolts without the hash marks are Grade 2.... been a long day.... Most 'real' shear bolts have no threads in the shear area, and only have enough thread on the end to put the nut on... The common bolts that people replace them with are what gets most people in trouble with hole elongation and since they usually have a long thread area, they tend to be weak in that area. But are lots cheaper...

 

[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.