Shear Bolt Broke On New Deck. PTO Shaft & Gear Box Holes Don't Align.

[bearthebruce]

I read all pages because I'm always interested in learning something I've never seen happen. My brush cutter has two blades that swing from one end of the blade. When I hit something, as too often happens, stumps and rocks, the blade gets nicked, but it swings out of the way. I thought they all were built like that; not so? Does that mean my type doesn't need a slip clutch or shear bolt?

Most are built as you described. You still need a shear bolt or clutch to prevent destruction to the gear box on the mower or the PTO of the tractor should something get caught in there and stop the rotation of the main mover of those blades.. Remember, you are dumping a lot of power into that mower. If things get bound up, they get messy.. right? Something has to let that power be dissipated and the swinging arms are not enough in all cases. The shear bolt or slip clutch protect the main power delivery systems from catastrophic damage.

 

[pop4dogs]

The tractor is a John Deere 990 and the Rotary Cutter is a Frontier RC2072. I bought the Cutter brand new in November of 2020. I used the cutter only about 6 times to mow a 2 acre pasture. I live in SW FL so the ground is relatively flat, soft and the pasture is just now starting to develop having previously been part of a nursery that we cleared and fenced for horses.

I was mowing last week and had 3 passes to do when I noticed the sound of cutting grass stopped. I looked back to see that about 60 feet of my current row had not been cut. Investigating I found the shear bolt in two pieces right under the gear box. I was a little perplexed by this because the mow deck this one replaced (another Frontier) came with the tractor and I had used it for over 10 years and in some pretty high, thick brush on other properties, numerous times and never once did the shear bolt break. I wasn't the only one driving and you know how other people are less careful with equipment that isn't theirs. And here I am with a brand new deck and a broken shear pin after only 6-7 uses on new pasture.

The original shear bolt is a 1/2"X3.5" grade 8 bolt. I looked without success to purchase one from various local Lowes Depot type stores. TSC had a pack of five, same dimension grade 2 bolts. I bought them because I was going to use them to keep me going until I could locate a grade 8 bolt. I called our local John Deere. They ordered me the recommended bolt for the cutter (which I bought from them). The guy first tried to tell me that the grade 8 bolt was wrong and that I should have a softer bolt. I asked him if this was the case then why did the cutter come new with a grade 8 bolt.

I have turned the PTO shaft to align the holes up to the shaft on the cutter gear box. They align perfectly from top of holes to bottom of holes but not from front to back. Neither the old bolt or the new bolt will move beyond the edge of the hole. It's not even a matter of a tight fit or getting half way and getting stuck. There should be a round hole to slide the bolt through but it looks like one of the two components is jacked at an angle. One one side it looks like the gear shaft hole is too far back at the front of the PTO hole and on the other side the Gear Shaft hole is too far forward in the back of the PTO hole. Is this a manufacture defect?

The original bolt has wear and damage at both spots where the holes would touch the bolt Is this normal wear? Notice how the PTO shaft has wearing on the front of the hole on one side, but on the other side it is at the back of the hole. Is this normal?

I would like to remedy this problem myself if I can. I would like to avoid taking it to the dealer because they will keep it for weeks before they actually look at it and another few weeks before they fix it. But if it looks like it's a defect issue then I'll deal with it appropriately.

I am including photos of the original bolt and images of the PTO shaft and Gear Box shaft holes from both sides. Your advice and wisdom is appreciated.

I have the same RC2072 for about 10 years now. I have a clutch to try and avoid shearing the 1/2" bolt. Have sheared it 4 or 5 times in pretty rough service anyway. I have replaced the stump jumper pan and even launched a blade. Bolt in tack blade split at the hole(Never found it either) Grade 8 is what I started with and what I have there now but grade 5 held up about the same. You just need a pointed taper pry tool to align the holes. There may be a little metal displaced that a rat tail file can clean up to. It's possible to gall the shaft and coupling it you are spinning it with out the bolt. My last break left the bolt in the shaft and cut both ends off. It still just required driving out the slug which aligned the holes and tapping a new one in.

 

[Gary Fowler]

It is obvious that part of the sheared bolt is stuck in the hole. Find a punch of equal or a bit smaller than the hole and try to drive out the stuck piece of bolt.

 

[Gary Fowler]

If punch fails, try drilling out the holes from both sides using a 1/2" drill bit.

 

[SPYDERLK]

To me a grade 8 is a pretty standard shear bolt, some times shear pins just want to be replaced. The fact that these holes are not lining up on either 180 degree suggests to me that they haven't been since new so putting the pin under more pressure (as it seems unlikely to be the pressure of work that broke it). I would re-drill the hole, I know that will affect the warranty but you have already proved it is not up to much anyway and you have a machine you can not use at the moment.

A shear shaft and mating collar that can handle a grade8 shearbolt is going to be very hard. - Drilling in place will take a carbide bit and good control to avoid breaking it. Perhaps a 1/2" double cut carbide round nosed burr could be run thru carefully to clean up the hole.