More Bush Hog shear pin issues.

[Tsagoth]

I read one of the other posts about mower shear pins and was a bit surprised. I've never heard of Grade 2 bolts nor Grade 10 for that matter. Anyway, I have a five foot wide bush hog that I've been using 3/8"x3" Grade 5 bolts in as the shear pin. I doubt the deck would even spin up with a Grade 2, lol. The problem is that I break bolts constantly, maybe four or five per hour. Now I'm not hitting rocks or otherwise stalling the blades from an impact as such. One of two things will break the bolt: heavy grass/weeds or a small sapling (3/4-1.5 inch dia.). The little saplings, what usually happens is I hear the bang as the mower cuts the tree off and the bolt breaks at the same time. The blades are still spinning after the bolt breaks, but it's irrelevant at that point.
The heavy grass/brush is the most annoying, at least with the little trees I can see them coming and raise the deck a bit. Yesterday I broke a two Grade 5's in twenty minutes, with the deck 9-14 inches off the ground mowing 4 foot high grass and whatnot, no dogwood or anything. I've tried Grade 8's in the past and they aren't much better, they are a little tougher, but they still snap on the little saplings and they are a d@mn sight more expensive.
I was about to replace the bolt with a plain steel rod, hammered over at the ends to keep it from falling out when I saw the post about Grade 10's, and the different sizes. It also occurred to me that maybe the cheap steel rods they sell here are no tougher than a Grade 5 bolt. Anyway, I've always used 3/8" carriage bolts because that's what this ancient deck came with, but given how loose they fit, a larger bolt might fit, so I bought some 7/16 and 1/2 inch bolts to try, and I have Grade 8's of both coming tomorrow. I'm sure the 7/16" will fit, less sure about the half-inch.
I'm using a 1970 (I think) IH 444 diesel to run the deck. I'm not too worried about stripping the gears out of, if it dies, it dies. I generally mow in 2 low, revs at near max. I can't tell you what that is, because the tach has been broken since I bought the tractor 27 years ago. 1 low is just too slow, and 3 low is too much for the heavy stuff, but it's fine for normal mowing. If I'm working near the treeline and the bush is all dogwoods and crap, then I'll shift to 1-Low, the tractor has to work pretty hard in that stuff.
So how much tougher is a Grade 10 bolt ? I was thinking of getting a skinny drawbar pin that would fit through the bolthole, I'm pretty sure that thing won't break even if I hit an anthill. Any other suggestions as to what else might not break as a shear pin ? I haven't yet looked into where to buy Grade 10 bolts, I'm hoping a fatter bolt will help.

 

[Ericp351]

Basics. Your grade 2 is just a cheap, upgraded bolt. Traditional shear pin stuff. Your grade 10 is unrealistic. Common graded bolts top out at 8. Would not be specified, any way. 3-8 is too thin, even for a "OK " grade China machine. My woods cadet, probably a bit heavier than yours, probably specked at half inch. Note, increasing diameter increases shear resistance faster than your buying hard, thin bolts. Baseline is soft bolt at max provided dia. Better is to adapt or upgrade to a clutch set up. Use one on my demolition work cutter. You adjust them by adding spring tension (squish). Good luck. Keep weak point adequately, but cheap. Your gear box , pto, or transition is not.

 

[joeysmith]

Had decent luck drilling them out an using the low grade bolts in the bigger size

 

[mhb@ufe]

It sounds like you are using the wrong size bolt. If a 7/16 will fit that is what you should use. If a 1/2 in will fit that is what you should use.

 

[Jim.ME]

Do you have the manual for your cutter and are you using the shear pins called for?

What make and model is it?

In the US grade 8 is a harder bolt. When you go beyond that it will be a socket head (12.9) unless you get a special alloy bolt.

Metric grade bolts are like 4.6, 8.6, 10.9.

You might consider investing in a slip clutch.

Worn out holes in the yoke and shaft increases breakage.

 

[Wdj]

If the bolts sloppy in the hole there's your problem. Grade 2 oughta work with snug fit. Mine uses 1/2 "
.

 

[lodoc]

Shear pin is your friend. It fails before anything else like the shaft, gearbox, etc.

There's something off with your dynamics. Too much power for your mower, angle of shaft, loose components, oblong holes, resistance from the mower or overtaxing it by expecting it to do too much (small mower / powerful tractor}. Suggest start from scratch regarding how your rig is designed to function, laid out, set up. Putting in a 'stronger shear pin' will lead you to expensive repairs and education.

 

[Tsagoth]

Well I tried some new bolts, and 1/2" will fit, the threaded part is snug, whereas the blank section slides easily enough. So tomorrow I'll take the deck for a spin and see how it does with the new bolt. The Grade 8 1/2" bolts arrive tomorrow as well, so if I snap the the Grade 5 I can try again with the 8. No, I don't have a manual for the mower, it has no markings or stamps anywhere on it, not even on the gearbox. I think I paid $50 for it twenty years ago at an auction. I'm not too worried about busting gears, the square baler will stall the engine outright when it suddenly jams choking on too much hay. The slip clutch on it only stops the PTO from forcing the baler to spin, it doesn't stop the baler from forcing the engine which is spinning at almost max rpm to go to zero rpm in a split second. So if the baler hasn't killed the tractor in these past twenty odd years, I'm not too worried about the mower killing it; I do a lot more baling than mowing. I don't mind the little trees snapping the bolts so much, but I will not put up with thick grass making them shear, that's just nonsense. Hopefully you guys are right and the 1/2" bolt will make all the difference. I'll find out tomorrow.
The other thought I just had is maybe replace the gearbox with something else. It occurred to me that if I could get the blades spinning at say 1500 rpm or better, then nothing short of a small tree should be able to stall the deck. The rivets holding the blades on look like 3/4", and the blades are 3/4" too looks like, so they ought to be able to take a lot of force. Something to think about anyway.

 

[Tsagoth]

Putting in a 'stronger shear pin' will lead you to expensive repairs and education.

I live by the motto "If it jams, force it. If it breaks, it needed replacing anyway.". I use a four foot two inch diameter steel pipe for leverage on my breaker bars, with the not uncommon result of snapping them off at the head, resulting in yet another warranty replacement, under the no-questions lifetime warranty for hand tools.

 

[Ray,IN]

Well I tried some new bolts, and 1/2" will fit, the threaded part is snug, whereas the blank section slides easily enough. So tomorrow I'll take the deck for a spin and see how it does with the new bolt. The Grade 8 1/2" bolts arrive tomorrow as well, so if I snap the the Grade 5 I can try again with the 8. No, I don't have a manual for the mower, it has no markings or stamps anywhere on it, not even on the gearbox. I think I paid $50 for it twenty years ago at an auction. I'm not too worried about busting gears, the square baler will stall the engine outright when it suddenly jams choking on too much hay. The slip clutch on it only stops the PTO from forcing the baler to spin, it doesn't stop the baler from forcing the engine which is spinning at almost max rpm to go to zero rpm in a split second. So if the baler hasn't killed the tractor in these past twenty odd years, I'm not too worried about the mower killing it; I do a lot more baling than mowing. I don't mind the little trees snapping the bolts so much, but I will not put up with thick grass making them shear, that's just nonsense. Hopefully you guys are right and the 1/2" bolt will make all the difference. I'll find out tomorrow.
The other thought I just had is maybe replace the gearbox with something else. It occurred to me that if I could get the blades spinning at say 1500 rpm or better, then nothing short of a small tree should be able to stall the deck. The rivets holding the blades on look like 3/4", and the blades are 3/4" too looks like, so they ought to be able to take a lot of force. Something to think about anyway.

Sounds like the ½" bolts you're using have rolled-on threads, bolt with cut threads fit correctly= same dia. from head to tip.
I always want the cheapest, easiest to replace part be the first to break. I carry spare ½"X 3½" bolts and Nyloc nuts in tractor toolbox all the time. I can replace one in 10 minutes and return to mowing.

 

[hurleyjd]

Try some longer bolts make sure that the length is sufficient that all of the un-threaded portion of the bolt is in place for it to shear in the un-threaded portion of the bolt and not the threaded part of the bolt.

 

[Ericp351]

I think I covered your issue reasonably well. Following responses repeated my points also. My logic is what ya paid for a tool is now irrelevant. Replacement cost, fair market current value, usefulness, cost of upkeep, et cetera , interesting. Sometimes. Bottom line, to run it properly ain,t that difficult. If breaking your own stuff is practically desired, weld her up. Easy. This is still America, just don,t tell the woke, weenies and revisionist. Your fight. Keep lube in the gear box, add a proper shear pin, and weld and police deck cracks and your good to go, usually for years.

 

[showcrop]

Are you tightening the nut onto the bolt with correct torque for its size and hardness?

 

[Ericp351]

Post script. I wanted to tap out of this silly thread thingy, but am now inclined to add one thing. I need not be part of a pending Darwin Award. In the unlikely event you figure out a way to spin at nearly 3x the advised rpm, and 2x the design Rpm, it will fail. It is also possible, probably unlikely, that it may take you out with it. Physics. Square function. Enjoy! If the Woke, milleminial type rainbow Post Police management need to pull these comments, so be it. Ain,t no shrapnel, blood on my hands this week. At least checking bolt torque will also prove most silly, irreverent. For the record, you confused a Slip clutch with an Overide clutch, above. Surprised the showcroppy didn,t notice.

 

[Texasmark]

Grade 2 smear when they shear rather than snap like higher torque range bolts.....makes finding the hole in the shaft to punch out the remnants easier to find. I had problems with bolts shearing (including Grade 5) on worn equipment until I used a self locking nut and didn't screw it all the way down....left it a little slack. Seems the action of a worn interface moves back and forth as the load/drive changes and that is what causes bolts to snap if high torque type and torqued down.

 

[paul]

This is a confusing issue/ thread.

Shear bolt needs to be the right size for the hole. Usually needs to be tightened tight, not loose. Holes need to be squared up round, not egg shaped.

Brush hog should rarely even shear anything, it has pivoting blades. If you somehow catch the spinner in the middle if it doesn’t have a stump jumper, I guess, otherwise bush hogs are designed to give without shearing 95% of the cases. One of the least likely implements to ever shear.

Do you actually have a finish mower with lawn mower blades?

Then, why are you talking about different sized bolts, or using hitch pins that wouldn’t clamp tight.

Shear pin fills the hole properly, and is tightened normal tight as you would a bolt.

Grade 2 is a common bolt, and often a good shear bolt that will cut, or shear, you will notice it bent sides a little as it shears.

Grade 5 is sometimes a shear bolt, they have less give or stretch, and more likely snap off straight and hard.

Grade 8 rarely is called for as a shear bolt, they are very tough but can be a little brittle and might snap on a shock load more easily than a grade 5 - depends on the way the shock hits it.

It is pretty common for us home owners to move up a grade in an effort to not break as many bolts. If a grade 2 is called for we cheat with a grade 5. It is what it is.

Grade 10 bolts are very special, can’t see them ever used on mass produced implements.

Reasons bolts break too often is:

1. Something overloaded.
2. Holes are deformed, egg shaped.
3. Bolt is too loose, or egg shaped holes create a stretched loose bolt.
4. too small for the hole.
5. has threads in the shear area where it should have full size smooth bolt at the snapping point.

Not picking on anyone here, just seems a lot going on that wouldn’t fit what should be going on.

Paul

 

[ford4wd08]

First, which type driveshaft do you have?

There are shear bolt protections that are perpendicular to the drive line, then there are shear bolts that are parallel to the driveline.

Mine is parallel and had a 6 spline with the push button lock on both ends of the driveshaft. One at tractor end and one at bush hog gear box end.

When I bought my 6 ft bushhog brand brush cutter used, someone had swapped the driveshaft around where the inner portion of the PTO shaft was driving the outer portion. This also made the parallel shear pin be at the tractor end of the driveline.

This made the shear bolt shear constantly on startup of the bush hog.

All this to say, make sure the driveline is installed correctly, and the outer sleeve is towards the tractor on the driveline.

 

[Tsagoth]

This is my little riding mower:

Well that was interesting, I can't believe I was so stupid. The 1/2" Grade 5 bolt worked just fine, I mowed all sorts of different stuff and I didn't break the bolt. A couple of times after a good bang, I looked back, sure I had snapped it, but it was still there. Never had to break out the Grade 8.
This is what snaps those 3/8" bolts. This one is a little on the large size, I wouldn't normally try to run this over, but even half this size will snap a bolt.

This is what the HOA would call "overgrown", also snaps 3/8" bolts. Those dogwoods can have up to 1/2" diameter trunks at ground level, easily snaps bolts if there's a bunch of them together.

Yes, the mower really is a bush hog, has the spinning disk with the two 3/4" thick blades that look riveted on, and swing freely when the mower is at rest. I usually torque the nut as tight as I can with a 12" ratchet, but occasionally the nut just spins off, even if it's a nylok. The bolts usually snap off at both ends, I'll find the head and say 3/4" of the bolt with the nut still on laying on the deck and the rest of the bolt is inside the pto drive. Once I line the holes up for a new bolt, the old one usually just falls out, but sometimes it's a little deformed and I have to poke it out with the new bolt.
Anyway, the problem seems to have been solved by switching to 1/2"x3" bolts. Good stuff, and thanks for the ideas.

 

[Texasmark]

Well I'm glad I backed out of this post.....it's getting complicated....and when I retired from industry in 2005 I decided I was tired of complicated calculations/situations!!!!!!!!!