What size of shear pin bolt??

[NewClimber]

This past weekend I was using my brush hog and hit a stump covered over by a bunch of back berry bushes. I was enough to stall my tractor but not break the shear bolt on the brush hog!!! Luckily everything seems to be still working.

My question is, I replaced the shear bolt last year after breaking it, and installed a #2 bolt that was I think 1/2" in diameter. Was this correct??? The 1/2" diameter was the same size that I pulled out, so I guess I am concerned that the #2 bolt was not correct. Do they make something different at tractor supply shops that is made for shear pin applications??? Thx

 

[Soundguy]

I'm concerned that your tractor didn't shear the pin vs stalling. Yes.. size the pin for the hole.. if it's a 1/2" hole.. use a 1/2" bolt.

Grade 2 is a good safe 'guess' if you don't know the manufacturer spec.

Double check that grade 2 bolt.. make sure it has no hash marks on it's head. Sometimes bolts get placed in the wrong bin.. etc.

Soundguy

 

[NewClimber]

I checked today and yes, the bolt has no marks on the head of the bolt. Any other suggestions?? It is a B7100 Kubota, maybe a smaller diameter bolt, or will this cause other problems??

 

[BB_TX]

I would not put a smaller bolt in the 1/2" hole. You may end up deforming the hole.
I am curious. Did it stop with a bang? Or did it lug down and then stop like within 2 or 3 seconds? Were you running at rated PTO rpms or slower? I am thinking maybe the blade(s) didn't actually slam into the stump, but the combination of the blackberry bushes and scraping the stump was enough to load it down slow enough to stall the tractor without shearing the bolt.

 

[NewClimber]

Good point about deforming the holes..I will keep the same size bolt.

I want to say a little of both...I definitely hit the stump but it didn't die instantly. I was at full throttle or at least just under full throttle, I usually go off of the sound from the engine but I was wearing ear plugs and just noticed that I was almost all the way on the throttle when I throttled back to restart the engine. I am somewhat new to using my tractor, just got it last year, and from reading I should be at 3/4 to full throttle when using the brush hog...is this correct? I was in some deep black berries so it could have been what you described. Last year when I hit a different stump it broke the shear pin right away. Scared the heck out of me, but I guess the shear bolt did it job. I was just out of commission until I could get to the hardware store.

Thanks for the advice and any other info please pass it my way.

 

[BB_TX]

My tach has a mark for rated rpm and another for max rpm. I set mine close to the rated mark when running the rotary cutter (or brush hog).
I shear 3 or 4 bolts a year so I keep several spare so I will have one when I need it. Reminds me, I need to pick up some more.

 

[RonR]

One of the things I did for my shear bolts (grade 2) was to spray paint the heads of the replacements I bought the color yellow. That way, when I see them around, I know what they are for and I also know not to put an unpainted one in for a shear bolt.

ron

 

[LoneCowboy]

The shear bolt can also get stuck (galled) in there and it won't rotate on it.
That's why most units have a grease zerk to grease that so it slips.

I use nasty worthless made in china cheap 1/2 bolts.
They shear really fast.

Which is perfect.

It's weird how sometimes you go for months without breaking a shear bolt, then you'll break 3 in a day.

 

[slaveToHorses]

I use nasty worthless made in china cheap 1/2 bolts.
They shear really fast.

Oh, you mean ANY bolt from Home Depot?

I also paint my shear pins, but for a different reason. When they shear I have a better chance of finding the remains. Don't what the disks,tiller or finish mower to find them for me.

One of these days I am going to break down and get a shaft with a slip clutch on it and be done with the shear pin thing.

 

[kenmac]

Oh, you mean ANY bolt from Home Depot?


Yep, that's the ones I use (1/2 ") & they will shear. I have replaced several