Shear Bolt.........Am I doing this right?

[DrRighteous]

The 4' Rotary cutter has a sheer bolt gear box. This I've not see before. The ones I've used in the past had splines. It didn't come with the shear bolt so off I go to Tractor supply to purchase them.
The shear bolts they had appear to be 5/16" bolts, but I found the hole in the input shaft is 1/2". I didn't think to much about it so I just put the bolt in.
Well, I've use the cutter probably an hour at the most, so far I have gone through 2 shear bolts. Is the size difference part of how the shear bolt action works, or am I suppose to have a 1/2" shear bolt for this thing and I just got the wrong size??

 

[SSdoxie]

The diameter of a shear bolt/pin needs to be same as the hole otherwise the movement between the shaft and PTO create it's own shear action. Use a soft grade (#3) 1/2" bolt with a self locking nut. Do not toque nut down tight, just snug it up.

My 4' TSC cutter also has a 1/2" bolt. I believe with a bolt this size the cutter was intended to have a slip clutch on it rather than rely on shear pin. I have stalled mine a couple times, it killed the engine before shearing the bolt. This is very hard on the tractor PTO drive. I was lucky no damage occurred.

 

[Ford850]

My King Kutter rotary mower uses the 1/2" bolts as well. TSC or Rural King bulk bolts, grade 2, are what it uses. I either punch the threads to hold the nut on, or use the nylon lock nuts. It only shears on sharp impacts, but it does shear occasionally.

 

[DrRighteous]

The diameter of a shear bolt/pin needs to be same as the hole otherwise the movement between the shaft and PTO create it's own shear action. Use a soft grade (#3) 1/2" bolt with a self locking nut. Do not toque nut down tight, just snug it up.

My 4' TSC cutter also has a 1/2" bolt. I believe with a bolt this size the cutter was intended to have a slip clutch on it rather than rely on shear pin. I have stalled mine a couple times, it killed the engine before shearing the bolt. This is very hard on the tractor PTO drive. I was lucky no damage occurred.

Yeah, I gotta have the wrong size shear bolt. That is the only thing that makes sense. This thing is breaking them too easily.
BTW, where are you on the Plateau?

 

[ch1ch2]

Are you engaging the PTO properly?
Slow engine, Slow engage letting the implement slowly start spinning.

 

[LD1]

^^^what they said. Need a 1/2" grade 2 shear bolt in a 1/2" hole. I think rural King sold 5pk of king litter brand shear bolts with nuts for like $7.99 last time I was there

 

[DrRighteous]

Are you engaging the PTO properly?
Slow engine, Slow engage letting the implement slowly start spinning.

Yes Sir.
This old tractor is pretty low tech. One of the things I like about it. Bare functionality. There is very little to break on it that cannot be easily fixed. It does not have a live PTO. I always engage the PTO at low RPM.

 

[KennK]

To be clear ... not all shear bolts are Grade 2. My CountyLine Post Hole Digger manual calls for a Grade 5 Hex Cap 5/16” x 3” bolt fastened with a lock washer and hex nut. Of course that is for a post hole digger - NOT a rotary cutter.

 

[newbury]

To be clear ... not all shear bolts are Grade 2. My CountyLine Post Hole Digger manual calls for a Grade 5 Hex Cap 5/16 x 3 bolt fastened with a lock washer and hex nut. Of course that is for a post hole digger - NOT a rotary cutter.

That probably should be rephrased to "not all equipment that requires shear bolts use grade 2 standard bolts".

As usual check the manual, there are some "shear bolts" made with grooves in them so they shear differently than the vanilla zinc bolts bought at TSC for about $2.50/lb (last time I looked). And some use different grades.

 

[PILOON]

Shear bolt need to cut clean otherwise burring will result making removal difficult.
Like scissors you need clean sharp cutting edges.
A soft bolt will stretch and bend B4 shearing but a moderate graded bolt will shear clean.
In my case I have found that grade 5 works best on my snow blower fan and later discovered that that was what was actually specked by the manufacturer, LOL that is what comes buying used equipment without any user manual.
At that the manuals probably only refer to a PN thus grabbing crazy profits on off shelf items.
On most snow casters (example) just about all parts are standard 'off shelf' components.
Very much like lubricants, as long as the spec is met you are good to go.

Years back courts fought and won cases that were fought over engine oil specs as some manufacturers attempted to deny warranty due to 'non OEM oil usage'. I suggest shear bolts would be in same category.