Rotary Cutter Need weaker shear bolt

[Snowman9000]

I have a 4' cutter on my JD 755. For a shear bolt where the PTO drive shaft connects to the gearbox, it came with a 1/2" bolt. The bolt head has no markings on it to indicate that it is high strength. It does have SJ stamped on it.

Anyway, the bolt is too stout. I have hit things that have stopped the motor, RIGHT NOW. Maybe it's because the tractor is on the small side HP wise. But whatever the reason, I need a weaker bolt.

Assuming it's just a plain steel bolt, what other ideas do you have? I can't say that I've seen brass or aluminum in half inch.

My best idea is to grind grooves in the bolt at the two spots where it needs to shear. Probably not a bad idea, but I'm open for anything else that has worked for you.

 

[Mousefield]

I have been looking for a ½ inch shear bolt for my auger, stores seem to carry grade 5 and up. My understanding, depending on the implement, grade 2 would be a good shear bolt.

 

[wrenchturner]

The SJ would be the manufacturer of the bolt. My guess is the pto shaft came off of a much larger bushhog it being 1/2 in diameter. Is it possible to drill another hole for a 1/4 bolt and place a grade 0 bolt in it. If too small then drill for 5/16.

 

[fredhargis]

How about a bronze bolt? In industry (at least in the one I participated when I had a day job) our shear bolts were all 1/2", but then we machined a groove into it that our engineers spec'd to give the right shear force for the machine. You could do this your self (I think) on a drill press using a small file.....though unless you do the calculations it would be a trail and error effort.

 

[Slacker]

Replace it with the same size bolt from Lowes or Home depot. They shear VERY easily on my 5ft Howse bushhog run by a 36PTO HP machine. I finally went and bought some grade 2 at Fastenall. I think the Lowes bolts are pot metal, but that may be a good thing for you're situation. Before you drill holes or buy expensive bolts, try the chinese crap that the box stores sell.

 

[kday64]

Have you verified that you have the correct bolt in place not just a bolt that fits.

The wrong type and strength bolt can result in injury to others.

What does your manual say?

 

[Snaker]

A 1/2" shear bolt on a 4' mower? Thats pretty big. Are you talking a 1/2" bolt diameter or 1/2" wrench size?

Are you sure that it is actually intended to be a shear bolt or could it be a mounting bolt.
If it is indeed a shear bolt, then you should see some sort of retaining setup (retaining clip?) to keep the PTO shaft from falling off.

 

[Transit]

Home D has a wide selection of bolts. The grade markings are a sires of lines on the bolt head. no lines indicates a grade 2 bolt.

 

[wrangler6831]

Tractor Supply carries grade 2 bolts. Replace it with a grade 2 and try it before you do anything else. We bought a brand new HOWSE and twisted the PTO shaft in too and also broke the u-joint. took the whole assembly back to the dealer and he accused us of replacing it with a grade 8. I suggest he look at his HOWSE on inventory and sure enough about 5 of them had grade 8 bolts. Howse stood behind it and gave us a brand new drive shaft with the correct bolts.and it shears them correctly now.

 

[unbidden]

I agree with using a grade 2 bolt. If that is still too rigid, just a thought, try using a fully threaded bolt. That at least in theory should break eaiser.