Shear strength of a bolt update

Went by the dealers yard today to ask him about the bolts he sells for my new cutter.

He said that he just buys a box of grade 2 bolts and nuts from bolt supplier and sells them for shear bolts. So I questioned why he sold grade 2 bolts for this cutter when the parts break down shows grade 5 bolts.

His comments were......
That cutter needs grade 2 bolts. Grade 5 will not shear quick enough to protect the mower.
He has even questioned the factory rep about the parts breakdown and was told the cutter was made for grade 2 bolts and could never get a good answer why the parts break down showed different.

He then showed me a new cutter with the factor supplied shear bolt.
It was a grade 2.
So while the factory parts breakdown shows grade 5 they ship the cutter with a grade 2 bolt.

So now that I know the bolts he gave me with the cutter were grade 2.
The mower has been preforming well with these bolts.
It shears the bolt if you hit something hard but does not shear cutting small trees up to the size the cutter is rated for.
I will be using grade 2 bolts even though the parts breakdown shows grade 5.

Thanks for all your help in this matter.

Very interesting. Thanks for the update.

Just a tip, I put a grease zerk on the yolk of my old cutter, so when the bolt shears it didn't weld itself together.

It never ceases to amaze me how dumb some OEM's can be when it comes to the equipment they make.

The other day I had a customer buy a brand new, $3000 plus, injection pump for his Komatsu excavator. The old pump had an electric solenoid activated start assist on it. It was normally off, came on when starting, and went off when started. The new pump had a hydraulic assist. It was normally on, but went off when it was hit with engine oil pressure.

The new pump came with no lines to update it, or anything other information. We weren't sure at first what was going on, but between a call to two fuel shops, and a stop at a hydraulic shop, I got it figured out and plumbed up.

Now I had called the dealership who, in turn, called Komatsu. According to Komatsu the part number on BOTH pumps was the same, and the new, hydraulic style, pump was what was supposed to be on the machine. and that's all they seemed to know about it... On the other hand, both the parts book, and the service book both show the electric type like we had just taken off.

No clue what the deal was, but we got it figured out. Funny though I've called mfgs many times over the years and been told that a part off their machine 'did not exist' even though I'm holding one of them in my hand. Like I said, it never ceases to amaze me....

Type-O?

I find the grade 2 bolts dont last more than a hour in heavy grass. The grade 5 will do light brush but still break in a couple of days of heavy work. If you only do grass fine. But if you have brush to clear, I have to replace bolts sometimes every 5 minutes. I just buy 10 grade 5 bolts at a time from tractor supply and leave them in the tractor with two wrenches. Since I am in 2 to 2.5 inch brush, they are going pretty fast. I have 600 acres of old pasture to reclaim.

I always used grade 2 on my baler I shared with a neighbor. He went to the NH dealer and got some, they were gr5. A soft bolt will shear under high but normal loads where a gr5 will not. Shear bolts are there to protect from shock loads.

More or less a typo, I've been shearing a few lately, and like you said it has to be something substantial, so it really works as it should, grade 2 bolts. Finally done clearing, and on the other tractor I have gone years without shearing one, seems the additional power/torque to the mower makes a difference when you hit a stump or larger tree. I'll often times just try to bend them over when working in reverse to keep the tractor out of the brush. Shred the top and listen to the mower, you can tell when its too much, lift up and drive away, but sometimes the remaining stub, will spring back and you catch it, that's when the bolt shears, did 2 of those in the same area yesterday. Vine covered/taken over trees, better to have sawed it off and run over the tops, but being so thickly covered I'll use the mower where it makes sense. Its nasty work, figured I'd widen things up and not have to deal with it again for a few years, at least the trees will be gone.

I remember well years go I worked for a NH dealer. A customer had a almost new baler and wanted to bale when it was very damp in the morning. Replaced soft bolts with grade 8! Gearbox ended up in about 3 pieces. The morning they blew it up it was so foggy we couldn't see 1 city block!!!

My JD has a slip clutch. Shear pins are not a problem. The extra expense of the slip clutch is modest compared to aggravation and lost of production.

I did the same (bought a bunch and put them on the tractor). Ever since I did that several years ago, I've only replaced one. I find that it's the tall grass that does it, not the occasional stump or large limb so I prevent it by taking smaller bites, moving to a lower gear.