shear bolt question

maxwell99

Well-known Member
I have a 3 pt hitch post hole digger.
its on the road a lot, if you know what I mean.

I want to be sure the shear bolt, from pto shaft to input shaft on the gear box, is the right hardness.

as I suspect, if anyone were to shear that bolt, they might pickup whatever they could find and keep on digging.

is the shear bolt a hard bolt or a soft bolt??

what grade??? and how do you tell a hard/soft bolt by looking?

so I can buy some extras bolts and let them go along with the digger, if a neighbor want's to borrow the digger.

bolts appear to be 5/16" bolts

thanks,
 
If it"s a common bolt, no special shoulder, it"s typically a grade 2, no markings on the head. Three slashes is a grade 5, six slashes is a grade 8.
 
Manufacturers, if they were smart, put in a hard bolt (grade 8) so someone could not put in one harder and tear things up.
 
I would find a spot on the frame to weld about 4 nuts. Thread in 4 new shear bolts and point them out each time you loan it out. A post hole digger is something that tears up easy if they use a grade 8 because it is just laying there. The other option is to thread some extras through the holes on an old leather belt and hook that up to it. If you want it to be treated right you have to supply the parts (sad but true).
 
But they can sell more parts when someone tears it up, or better yet they occasionally make the shear bolt a unique diameter so you need to buy it from them
 
I use the cheap grade that TSC sells. Must be ok. I'll shear one every now and then but haven't damaged the digger yet. I've gone this route for a long time. I tape a few extras on the frame.
 
I sold my 3PH digger cause I didn't want the liability of lending it out to a fool. Most dangerous machine on the farm. Now I dig with a hydraulic powered front mount, on the skid loader. You can't get off the machine, without the bit stopping.
 
(quoted from post at 16:28:16 07/15/13) If it"s a common bolt, no special shoulder, it"s typically a grade 2, no markings on the head. Three slashes is a grade 5, six slashes is a grade 8.

+1 on this reply. Grade #2 is what you want. It will be the smooth head with now dash markings. The Cheap grade of bolts at TSC.

FWIW: I also make a wrap or two of duct tape around the entire shearbolt jounal after installing a new bolt. Why: My post hole digger flings the bolts like a bullet when they shear. While it will not fling them at the tractor operator, it will fling them to the sides so if you have any helpers around could cause injury. Or it flings them hard enough to dent a car or metal siding on a barn. One of two wraps of duct tape helps prevent this and catches the broken pieces too boot.
 
with a little research I found this:

http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

hope it opens for you as it shows the bolt hardness markings

so currently I have a grade 5 bolt in the shear bolt location.

but the two bolts that I have in my tractor tool box for backup replacement shear bolts are grade 8.

so I need to buy softer replacement bolts as backups.

Thanks for your help on this:

replacing a soft shear bolt is much easier than replacing a busted gear.
 

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