Shear bolts - Grade 2 or Grade 5?

Big Trees · May 19, 2016

Hello to everybody. I know some people use grade 2 and some use grade 5 for shear bolts with a bush hog. What do you all use?

Grade 2 seems to be too soft, but is grade 5 too hard?

Thanks in advance!

BarnyardEngineering · May 19, 2016

Shear bolts are there to protect the machine from more severe damage. Using too hard of a shear bolt will generally result in something else like an expensive gearbox, or even the PTO on the tractor, getting damaged.

Your bush hog likely requires a special grade shear bolt somewhere between 2 and 5. They probably cost $3 each at the machinery dealer, which is why you are trying to use $3/lb grade 2 bolts.

IMHO, you've got a choice to make:
1. Constantly be replacing bolts.
2. Chance breaking something really expensive.
3. Use the right bolts even though they are more expensive.

Big Trees · May 19, 2016

(quoted from post at 07:01:08 05/19/16) Shear bolts are there to protect the machine from more severe damage. Using too hard of a shear bolt will generally result in something else like an expensive gearbox, or even the PTO on the tractor, getting damaged.

Your bush hog likely requires a special grade shear bolt somewhere between 2 and 5. They probably cost $3 each at the machinery dealer, which is why you are trying to use $3/lb grade 2 bolts.

IMHO, you've got a choice to make:
1. Constantly be replacing bolts.
2. Chance breaking something really expensive.
3. Use the right bolts even though they are more expensive.

Thank you for the reply, BE. I didn't know there were specific bolts that I needed. I thought grade 2 or 5 was my options. I will call the dealer and see what they say.

I appreciate that.

Big Trees · May 19, 2016

I called Kubota since that's the brand of tractor in question and they didn't know the grade of bolts they sell LOL they said they get them from Bush Hog. Since that's the brand of rotary mower in question I called the local Bush Hog dealer and he said to use grade 2 but if that's breaking too easy to try grade 5 but don't go over grade 5.

I explained my situation to the Bush Hog guy and he confirmed that the bolt that I was asking about is not being used as a shear bolt, it's only holding the shaft onto the tractor pto since the shaft splines would take on the pressure and not the bolt in the case of hitting a stump.

I will be replacing the "shear" bolt on the mower though because I'm not sure what grade that one is.

WI Dan · May 19, 2016

Interesting...thanks for the follow-up.

RustyS · May 19, 2016

The one thing I would add to BE's list would be a slip clutch on the drive shaft. You do have to slip the clutch before season. IT is nice to know your machine is protected and that you dont have to replace a bolt when you run over an unseen object.

jeffcat · May 19, 2016

The bolts are really cheep. Case 2 and be happy not to break some high dollar item.

Big Trees · May 19, 2016

Does anybody know the name of the "c shaped" clip that holds the pto shaft to the mower gearbox when a shear bolt fails?

A picture would be even better if somebody has one available. I'm trying to find out what they are before I head up to TSC. You know they won't know if I describe it to them! LOL

Any help is greatly appreciated!!

Russ from MN · May 19, 2016

I think you are talking about an external snap ring, Google it and find out! You need to know the shaft size. Use grade 2 shear bolts only unless you want to replace some more expensive parts!

David G · May 19, 2016

I like the grade 8 ones.

Note, do not take this seriously.

Big Trees · May 19, 2016

(quoted from post at 10:48:59 05/19/16) I think you are talking about an external snap ring, Google it and find out! You need to know the shaft size. Use grade 2 shear bolts only unless you want to replace some more expensive parts!

Thank you, Russ. I was told about it but the guy didn't know the name. They said I didn't have one and needed one unless I wanted to die after a bolt sheared. I don't want that. On to find out where I can buy one at. Thank you!!

James Howell · May 19, 2016

We buy grade 2 by the pound; much cheaper than gearbox or JD PTO parts by the piece.

Ken Macfarlane · May 19, 2016

Read the manual. We had a MF baler that went through shear bolts like candy. Turns out we were using grade 2 where it calls for grade 5. The soft bolts had smeared when they
broke and damaged the shear bolt mechanism too because they would bend over and stick out beyond flush while the flywheel spun down. Pain to remove too.

Big Trees · May 19, 2016

I called 3 local Bush Hog dealers and got 3 different answers.

1 said - Use grade 2 and nothing else
2 said - Use grade 5 and nothing else
3 said - Use grade 2 and if those shear easy then use grade 5

So I called Bush Hog corporate in Alabama and the gentleman told me to use grade 5. He said grade 2 will shear way too easy and it bends usually instead of shearing. He said grade 5 shears properly and isn't too hard or too soft.

There was a grade 5 in there when I bought it used so I'll leave the 5 in there.

Thanks to you all

David G · May 19, 2016

I put a slip clutch on mine and used the shear bolt as backup, get on/off a lot less now.

notjustair · May 19, 2016

Not once in 40 years have I broken a shear bolt on
a mower - and I have three between five and fifteen
feet. I'm pretty finicky about keeping mowed down
areas free of obstacles. I've broken a couple on the
post hole digger and a slew of them on the 24T
baler, but I get those flywheel bolts right from
Deere.

jm. · May 19, 2016

IF you are breaking the one at the tractor It would be safe to bet you need to grease the slide part of you PTO shaft. No reason for the bolt that holds the joint to the tractor to shear unless the shaft is TOO long and when you lift the unit you are shearing it or as you lift and lower the shaft is binding and causing that bolt to break. Most cutters come from the factor with grade 2 but folks move up to grade 5 pretty quick. Think you got the right answer from the bush hog guy.

rpllr · May 19, 2016

Just a note, the MF baler shear bolts that Ken McFarlane talked about
are Actually a special size from Massey. They are a little bit bigger
than 5/16 and using a small bolt in the hole let's it shear easily
especially on a baler.

Den N Ms · May 19, 2016

Big Trees ,If you are shearing the bolt off at the PTO shaft at the tractor connection.The PTO shaft is to long and is binding when you are raising the hog up with the 3ph.If that is what it is doing,then you need to slide the PTO shaft apart and cut a inch off each of the shaft ends that will let it go 2" closer together and not bind the PTO when raised up.

MarkB_MI · May 20, 2016

This is one of those perennial questions that pops up every so often with little agreement and no resolution. I use grade 5 bolts on my brush hog, which gets pretty rough service. I'd be replacing pins hourly if I used grade 2. Obviously softer bolts would be easier on the gearbox.

I try to avoid using grade 2 fasteners for ANYTHING. I like to think of them as "grade UNKNOWN", because you really don't know what you're getting when you buy Chinese "grade 2" bolts at your local hardware store. After all, a grade 2 bolt has no markings.

Big Trees · May 20, 2016

Great posts. I expected I'd get different opinions but I surely welcome and respect every single one.

Den n Ms - I will look into that and see if that's my problem or not, thank you. The bolt I was using to keep the shaft to the pto was a thin bolt, probably too thin and soft to hold the pieces together. It was just a regular soft bolt and it was only 1/4" thick. I think maybe I was asking too much from that little thing.

I put the grade 5 bolt back in that place to keep them connected. I hadn't had a problem using that bolt, only the other one, which was thinner and softer.

Thank you all for your replies

WI Dan · May 21, 2016

Lots of good ideas on this topic. I'm watching close...still haven't decided what my opinion is! It probably depends mostly on how the implement is used.

Shear bolts - Grade 2 or Grade 5?

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