Shear Pin question

[Typhoon]

Obviously this is my first tractor. I have been doing a ton of research and through reading and word of mouth I have learned about the shear pin on the pto shaft that is supposed to shear before any of your major components are damaged. Anyways, my question is, 1. How often does a pin get sheared? Is this something that happens all the time, or very rarely (im asking those of you who have had rotary cutters for years).. and 2. Is the shear pin what I think it is? Just a grade 3 bolt that you can get at the hardware store or is it a special part? And 3. Is it a big ordeal to replace one or an easy task? Thanks and sorry for so many questions.
-Brad

 

[RonR]

My guess is mowing, the only time you would shear it is when you hit something.

My post hole digger has one, but haven't used it enough to know how often they shear.

The plan is they shear prior to any components breaking.

The grade of the bolt is what's important and you MUST use what the manual specifies UNLESS you want to have the bolt NOT shear and something break.

My PHD uses a 3/8 GRADE 2 bolt. I plan to buy about 6 of them and spray paint them YELLOW, so there's no danger of me replacing it with a grade 5 bolt.

Best wishes.
Ron

 

[Bird]

1) There's no pat answer. If you're in an area with rocks or you hit something solid, you may break a shear bolt. Otherwise . . ., well, I've never sheared one on any of my equipment even when I backed into a chunk of concrete I didn't see and once ran over a pile of 2 x 4s I did see. The one and only time I sheared one was on my neighbor's hay baler (failed to notice the bale starter didn't fall back into place when I dumped a bale).

2) Grade 2 bolt instead of 3; buy them at the local hardware store.

3) It may fall out, but there's a better chance that it won't. Just manually turn the PTO shaft until it lines up with the broken bolt and punch out the remainder of the broken bolt. You might want to use a drift pin and hammer, but if everything is lined up right, you can probably just insert the new bolt, tap it into place and it'll push the broken piece out.

 

[jinman]

Brad, I use a bolt that I think is grade 2 (no marks on the head) and they are bulk stock at Tractor Supply and most hardware stores. Depending on the type of cutting I'm doing, I can expect to break no shear bolts or several. Last weekend I broke four while cutting in some particularly rough areas with hidden rocks and stumps. I always carry about 3 or 4 spares in my toolbox. I also carry a punch, very large screwdriver or pry bar and a set of channel-lock pliers. When the shear pin snaps, the collar slips around the gearbox's input shaft and traps a small piece of the shear pin. You must move the u-joint collar or rotate the blades by hand to get the hole exactly positioned over the broken shear pin. Only then can you drive the piece out and replace it with a new shear pin/bolt. I always select a bolt between 1/2 and 1" longer than the collar's diameter. After putting on the the nut on the shear bolt, I grip the threads sticking out with the channel-locks and crush the threads to provide interference with the nut when it tries to loosen. Otherwise you will have to use expensive aircraft locking nuts with a nylon insert. I'm cheap, so I just crush the threads. /forums/images/graemlins/shocked.gif /forums/images/graemlins/blush.gif

A problem can occur if the collar is new and very tight on the input shaft to the gearbox. You'll need to slide it forward (away from the gearbox) until it hits the lockring on the front of the input shaft. That's about the correct position so you can get the hole directly over the sheared pin. This is what takes practice and the job is sometimes harder becase the PTO shaft locks at the tractor when it is disengaged. I used to carry a small pipe wrench with me to grip the gearbox's input shaft between the collar and the gearbox. I could turn the gearbox instead of the PTO and easily match the hole location. I'm sure you will hear several good solutions for this "exercise," but with experience, you'll find which method works best for you.

Here's hoping you never, never break a shear pin. /forums/images/graemlins/grin.gif ...but that is probably not going to happen. I joined the two-dozen-club a long time ago. /forums/images/graemlins/tongue.gif

 

[jinman]

Hey, Bird. Did you notice our posts have the same exact time? You must have hit the continue button only a split second before me. /forums/images/graemlins/smile.gif Hope your 4th was good. /forums/images/graemlins/grin.gif

 

[Gary_in_Indiana]

Shear pins are just regular hardware store bolts of whatever grade the implement manufacturer chooses. They will always shear at exactly the most inopportune moments and you will always need exactly one more than you have on hand to complete any task.

 

[Bird]

Yep, Jim, had a good 4th with kids and grandson, then just got back today from going down in the country to visit our former nearest neighbors and friends. No sign of rain here, but drove through a frog stranglin' gulley washer between Hillsboro and Alvarado, and several other pretty good showers, including the west side of Grapevine.

Hope your holiday weekend went well, too.

 

[Trev]

Hmm.. anyone know if a Deere 4300 has one of these shear pins? I ask because from time to time I've picked up a rock in my tiller, and what happens is that the tiller stops dead, and the tractor just slowly lugs down. I just shut off the PTO in time and it will stay running. Now if I had a shear pin, I assume stopping a tiller dead would shear it.. so I'm guessing it's some kind of clutch arrangement rather than a pin? I should look this up in the manuals. Maybe the clutch is part of the tiller rather than part of the PTO....

Bob

 

[Bird]

Bob, if you sheared a pin, the PTO shaft would continue turning and usually no load on the engine. If you have a slip clutch you should be able to see it on the PTO driveshaft to the tiller, should be towards the tiller end of the shaft.

 

[kubotasaurus]

I went through 3 shear bolts on my post hole digger today while putting in another 50 feet of fence. I've probably been through several dozen with this implement. The ground on my property is hard clay and lots of rocks!

Easy to replace them - I just carry a ratchet with the right size socket with me and half a dozen shear bolts, nuts and split washers.

First, make sure the PTO is disengaged. Better still, turn the engine off.

In the thrill of the moment, with the engine running, the PTO shaft shielding on and the Post Hole Digger (or whatever) just having made a big thwack noise you can forget to do this. You won't forget it if you take a peek inside the end of the cover to replace the bolt without disengaging though! You'll get flipped around like something out of those karate movies if you get your hand in there!

I cheat a little with the post hole digger. The bolt hole is a bugger to get to unless the PTO shaft is lined up just right with the guard. I usually engage and disengage the PTO a few times at low engine revs and each time go back and check the alignment. It's easier than skinning my knuckles wrestling with pipe wrenches / screwdrivers or whatever.

I also leave the post hole digger in the elevated position so once the PTO shaft is lined up with the guard all I have to do is rotate the auger by hand to get the internal bolt hole lined up. This all sounds involved but is quite quick - only takes a couple of minutes.

I put a split washer on my bolt and use that to punch the center section of the old bolt out. I then put another split washer on the other end along with the nut, tighten up and back to the digging.

What takes a heck of a lot longer is getting the auger out of the ground if it's really screwed in tight on a tree root or something. Always take at least an 18" pipe wrench with you. Preferrable something bigger! You won't regret it.