Shear pin for rear cutter

Gun guru · Sep 11, 2011

I broke the shear pin on my rear cutter a few weeks ago. However, I put a low quality carriage bolt in place of the shear pin. I decided to get a real shear pin at TSC and they sell a set of 5 grade 2 1/2" bolts with lock washers and nuts. Now Wouldnt you want a 1/2" bolt with a .125" hole in the center so it is the weak point? Is the grade 2 bolt weak enough?
What do you guys use?

Aaron SEIA · Sep 11, 2011

I would want watever the mfg called for as a shear bolt. 1/2" anything sounds pretty big to be a shear bolt, but if that's the size of the hole then thats what has to go in it. I've never seen a special bolt with a hole in it to make sure it's a weak point. Buit there are a lot of things that I haven't seen.
AaronSEIA

BushogPapa · Sep 11, 2011

If the weaker Grade 2 bolt does the job, I would prefer it to a Grade 5, for a Shear bolt..
Now, if it shears too often, maybe the called-for Grade 5 would be a good choice..

Ron..

Paul from MI · Sep 11, 2011

I have seen shear pins/bolts for industrial applications that had the diameter reduced or turned down at the shear point to make the shear torque more consistent. I have never seen one like this in an agricultural application. If tthe shear pin holes get worn or distorted from having been shorn many times it will make the pin shear at lower torque than expected, Sometimes the pin holes are in bushings that can be replaced for that reason.

JML755 · Sep 12, 2011

(quoted from post at 21:06:18 09/11/11) I broke the shear pin on my rear cutter a few weeks ago. However, I put a low quality carriage bolt in place of the shear pin. I decided to get a real shear pin at TSC and they sell a set of 5 grade 2 1/2" bolts with lock washers and nuts. Now Wouldnt you want a 1/2" bolt with a .125" hole in the center so it is the weak point? Is the grade 2 bolt weak enough?
What do you guys use?

I just use 1/2" bolts from the hardware store, making sure they're not Grade 8. I don't shear many on the cutter anymore, since the ground I'm cutting has been pretty cleaned up by now of logs, stumps and other hidden gems like cinder blocks. I expect I'll shear more in the future as I've got about 10-15 acres that I've never touched and is pretty tall and overgrown. Probably get to it next year and I'll keep a bunch of bolts on the tractor. I shear more on the post hole digger nowadays.

As for your question on the hole, it would certainly weaken the bolt and is easy enough to do on a drill press, so might give one a little more peace of mind.

However, I can't ever recall hitting something where I thought the shear bolt should have broke and didn't. Most stuff I hit nowadays (limbs and such) just makes a big clatter as it gets run over. :lol:

souNdguy · Sep 12, 2011

all the mowers I have that use shear bolts, use the soft grade 2 bolts.

never had a problem cutting them when hititng something.

soundguy

David G · Sep 12, 2011

My King Kutter 5' rotary cutter had grade 2 1/2" bolts for shear pins. I got tired of that and bought a slip clutch.

Shear pin for rear cutter

Gun guru

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Aaron SEIA

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BushogPapa

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Paul from MI

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JML755

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souNdguy

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David G

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