Never heard of it.

[PitbullMidwest]

I started brush cutting this past weekend and with about 10 minutes left to cut I broke a shear pin.

No problem, run to Farm King and get another one, right? Wrong. To my amazement not a single employee knew what a shear pin was. "Never heard of it" was a popular response. I'm not talking about teenagers working part time, these guys have worked there for years. When I explained that the pin went in a PTO shaft and what it was for, they recommended that I go to a machine shop that specializes in drive shaft repair. Unbelievable.

I ended up sticking a bolt in it just so I could finish up but I know the grade is too hard to keep using.

So, where can I get shear pins or what grade bolt could be substituted?

 

[bandit67]

Take this for what it's worth as I'm no bolt expert, but the last time I broke a shear bolt on my tiller and couldn't get another one until the next day, I was told by the parts guy at a tractor dealership that I could use a Grade 8 bolt in a pinch.

When I said "what?!", he said the grade 8 has an extremely high tensile strength, but a lower shear strength than the grade 5 bolts, so would be safer in a pinch.

 

[VinnieNC]

I would have to call BS on using a higher grade bolt for a shear pin. Right now I am working on getting my Woods finish mower back together. I replaced the Grade 2 bolt with a grade 5 at the advice of the counter guy of my dealer a few years ago. I had sheared a couple grade 2 bolts and he told me I could increase to grade 5 and be ok. So I did. I managed to shear one or two of the grade 5 bolts, but rarely. Over the weekend, while mowing I had hit several red ant hills about 8 inches high. I mow at 2 inches. Later, I scalped a high patch of ground and stripped the bevel gears inside the gearbox. Gears alone are not replaceable, they are welded to the shafts, so shafts and gears are replaced together. Add in the cost of bearings and seals plus labor will cost upwards of $600. Woods has re-designed the replacement gearbox for this mower, but to use it, I will also have to upgrade the yoke on the gearbox end of the driveshaft. This $0.50 bolt is going to cost me around $500.00 after taxes and shipping costs.

Either use the correct manufacturers bolt or a grade 2 or less as a temporary substitute.

Upon re-reading my reply, I should have mentioned that I am not sure about the grade 8 bolt and it's tensile strength, as I am no expert either. I am just frustrated at my own stupidity and ruining a good gearbox, not to mention the cost of this lesson.

Personally, I will never do this again, not even in a pinch.



-Vinnie

 

[wushaw]

Grade 2 bolts are your sheer pins. Buy a bag of em or get a slip clutch.

 

[bandit67]

I used the grade 8 to finish tilling the garden. The next day, I picked up a 10-pack of the Grade 2 shear bolts.

Warning: 10-packs of shear bolts make you generous in handing out bolts to friends who are in a pickle. Suddenly you realize that your 10-pack is now a 4-pack, and you've only used 1 bolt out of the pack. I suggest getting two 10-packs, unless you have no friends (with tractors).

 

[PitbullMidwest]

I Googled "bolt grade shear" and it led me to Portland Bolt & Manufacturing Co's website which states:

Bolt Shear Strength Considerations
Question: What is the shear strength of carbon steel bolts?

Answer: First, unlike tensile and yield strengths, there are no published shear strength values or requirements for ASTM specifications. The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-2) states that shear strength is approximately 60% of the minimum tensile strength.

"As an empirical guide, shear strengths of carbon steel fasteners may be assumed to be approximately 60 percent of their specified minimum tensile strengths. For example, an SAE grade 5 hex cap screw has a specified minimum tensile strength of 120,000 psi. Therefore, for design purposes, its shear strength could be reasonably assumed to be 70,000 psi."

An SAE 7/16" grade 2 bolt has a Tensile Strength Min (psi) of 74,000lbs meaning that the calculated shear strength is 44,400lbs.

The SAE grade 8 bolt that I substituted has a Tensile Strength Min (psi) of 150,000lbs meaning that the calculated shear strength is 90,000lbs

I think I'll pick up a hand full of grade 2 bolts on the way home tonight.

 

[RobJ]

I would have to call BS on using a higher grade bolt for a shear pin. Right now I am working on getting my Woods finish mower back together. I replaced the Grade 2 bolt with a grade 5 at the advice of the counter guy of my dealer a few years ago. I had sheared a couple grade 2 bolts and he told me I could increase to grade 5 and be ok. So I did. I managed to shear one or two of the grade 5 bolts, but rarely. Over the weekend, while mowing I had hit several red ant hills about 8 inches high. I mow at 2 inches. Later, I scalped a high patch of ground and stripped the bevel gears inside the gearbox. Gears alone are not replaceable, they are welded to the shafts, so shafts and gears are replaced together. Add in the cost of bearings and seals plus labor will cost upwards of $600. Woods has re-designed the replacement gearbox for this mower, but to use it, I will also have to upgrade the yoke on the gearbox end of the driveshaft. This $0.50 bolt is going to cost me around $500.00 after taxes and shipping costs.

Either use the correct manufacturers bolt or a grade 2 or less as a temporary substitute.

Upon re-reading my reply, I should have mentioned that I am not sure about the grade 8 bolt and it's tensile strength, as I am no expert either. I am just frustrated at my own stupidity and ruining a good gearbox, not to mention the cost of this lesson.

Personally, I will never do this again, not even in a pinch.



-Vinnie

Vinnie,

I think you mower was about to have issues anyway. IMO you should not break a shear bolt by hitting an ant bed or a scalp. And certaintly not tear up a gearbox. My 4' bh has a 7/16" or 1/2" shear bolt!!! Never broken and I've wacked 2" trees before, I even put the question to TBN asking if it was to big. I think a grade 2 is the regular bolts you get from the big box stores.

Sorry to hear about your Woods, I have an RM360...using the loooong belt and the huge pulley. The pulley is driven by a straight shaft from the pto shaft. If I hit something I might just get a little belt squeak if it stops for s second. An old design (1999) but simple to.

Good Luck,
Rob

 

[Page2]

I started brush cutting this past weekend and with about 10 minutes left to cut I broke a shear pin.

No problem, run to Farm King and get another one, right? Wrong. To my amazement not a single employee knew what a shear pin was. "Never heard of it" was a popular response. I'm not talking about teenagers working part time, these guys have worked there for years. When I explained that the pin went in a PTO shaft and what it was for, they recommended that I go to a machine shop that specializes in drive shaft repair. Unbelievable.

I ended up sticking a bolt in it just so I could finish up but I know the grade is too hard to keep using.

So, where can I get shear pins or what grade bolt could be substituted?

Have a Tractor Supply or Farm and Fleet around? They carry shear pins. But then you would think any "farm" store, such as Farm King would.

 

[PitbullMidwest]

Have a Tractor Supply or Farm and Fleet around? They carry shear pins. But then you would think any "farm" store, such as Farm King would.

Unfortunately, no. The closest TSC is 45 minutes away and the closest Farm & Fleet is an hour. There was a time when Burlington had a Farm King, Orscheln, Town and Country and a Big Bear store. Now we're down to just Farm King.

 

[oliver28472]

Just about any place that has a decent bolt supply should have grade 2.