Best Guess for PTO Shear Bolt

[Beltzington]

I would go with a grade 2, 3/8, and if you start shearing bolts under normal load then go up to grade 5.

Concur, bolts are cheap, belts and gears not so much. Besides look at it as your daily exercise, cardio and legs getting on and off the tractor and flexibility and arms turning the PTO shaft to align the holes. Also, after mowing the field a couple times you will have found and eliminated most the obstructions, I havn't sheared a grade 2 bolt in at least a dozen mowings.

 

[CobyRupert]

Well - - IMHO - what does your Chinese Op manual have to say about the shear bolt. I've had three implements with shear bolts - 3-point snow blower- Grade 2 Wallenstein Bx42S- Grade 5
Walenstein BX62S- Grade 8. Sooooo.........what do I know.

Probably:

使用最适合拖拉机马力的剪切螺栓。

 

[Citydude]

Probably:

使用最适合拖拉机马力的剪切螺栓。

If I close one eye, I can read that.

 

[Slowpoke Slim]

No way in h*ll I'd put a grade 8 bolt in a Chinese gear box shear bolt. Don't know how you say "BOOM!" in Chinese, but I bet you'll be able to tell me after you try it.

Start with a grade 2 bolt.

Maybe go up to a grade 5 if you're breaking them under "normal" use, but no way would I go grade 8.

 

[CalG]

No way in h*ll I'd put a grade 8 bolt in a Chinese gear box shear bolt. Don't know how you say "BOOM!" in Chinese, but I bet you'll be able to tell me after you try it.

Start with a grade 2 bolt.

Maybe go up to a grade 5 if you're breaking them under "normal" use, but no way would I go grade 8.

From the description by the OP, this is the PTO shear pin.

Run the numbers on shear values if you want, but with a 100 hp tractor, a 3/8ths ungraded bolt will like last half as long as it takes to get the flail hammers up to speed.

But it is safe to start with a weak link and work your way up. ;-)

If the shear bolt were large diameter, I would rethink the implications.

Devil is in the details, but even the Chinese have good steel. They just don't sell it to US. ;-)

 

[4Papa]

Unfortunately, the manual (neither operating or parts) even indicates it uses a shear pin. So, I知 on my own to figure out what it uses.

 

[CalG]

Unfortunately, the manual (neither operating or parts) even indicates it uses a shear pin. So, I知 on my own to figure out what it uses.

Make sure the shear bolt fits the hole! A sloppy fit does not reflect clearly on any bolt grade selection. And TIGHTEN that nut! Torque it to spec.! (whatever that may be ;-)

Chi-com! I hate it all.

 

[Fallon]

Make sure the shear bolt fits the hole! A sloppy fit does not reflect clearly on any bolt grade selection. And TIGHTEN that nut! Torque it to spec.! (whatever that may be ;-)

Chi-com! I hate it all.

A sloppy or wallered out hole gives the shaft a running start to begin sheering that bolt. If it's not tight in the hole it will be failing prematurely.

 

[Rock knocker]

PTO shaft shear bolts are often grade 8

You could do the math, but a 10mm grade 8.8, or 3/8 " in grade 8 (if that is a good snug fit in the holes) is where I would start.
100 hp is gonna take some toll on an ungraded piece of steel wire.

Note : grade 8.8 is 120ksi material while Grade 8 is 150ksi. so not that much to say one over the other as far as "strength" goes.
shear being about 75% of tensile.

Anecdote: Meteor Snow blowers use grade 8 or 8.8 shear bolts on the PTO. ungraded (G2) for the fan and auger.

Boy, we have different math. I get that a metric Class 8.8 is about 87,000psi, which is about the same as a SAE Grade 5

I have never seen a SAE Grade 5 used as a shear bolt

 

[CalG]

Boy, we have different math. I get that a metric Class 8.8 is about 87,000psi, which is about the same as a SAE Grade 5

I have never seen a SAE Grade 5 used as a shear bolt

Right

Grade 5 and grade 8.8 are both about 120ksi material.

I just read from the first google return
Grade 5 vs Grade 8 Fasteners - TineLok
I have no reason to question the source.

Of course, there is not 1 square inch of material to shear in a 10 mm bolt, and shear is always some percentage less than tensile. Call it 70%, or so. Absolute shear values are never called out for commercial values that I have ever seen, and I worked in aviation for many years.

Regarding grade 5 in shear applications, Around here, when people get sick and tired of replacing pricey shear bolts in their sidewalk snow blowers, they often put in a grade 5 bolt and call it done. I'm not in support of that, but it is "seen". ;-)