shear pin vs. slip clutch

[TomG]

Shear pins are on the PTO shaft. The ones perpendicular to the shaft on the spline collar. Maybe there are other arrangements as well.

Decent bolts are made with an ID code on the head so you can tell exactly what a bolt is, if a bolt book is available. I wish I had one when I worked on early '70's British motorcycles. Sometimes you could find American SAE, several metric standards and British Whitworth bolts on the same machine.

 

[W5FL]

SAE bolts are marked with the marks on the bolt head, ungraded are kinda use at your own risk - made from old beer cans. /w3tcompact/icons/laugh.gif See post below for details. (the edit function is great)/w3tcompact/icons/smile.gif

 

[MChalkley]

Wen - Actually, the marks are:

None, no writing - Could be Ungraded, Grade 1, 2 or 4
3 Marks, equally spaced, no writing - Grade 5
3 Marks, all on one side of the head, no writing - Grade 5.2
5 Marks - Grade 7
6 Marks - Grade 8

There are others, but they're specialty bolts that aren't very common. (Actually, the Grade 5.2 bolts aren't real common, either.) But the important thing to remember is that 6 marks is Grade 8, not Grade 5 and should never be used as shear bolts unless they're specifically recommended, which I've never seen.

Mark

 

[W5FL]

Oops...The only ones I have ever used were the 1/2 hard (3 marks on head) and the hard bolts (6 marks on head) and the ungraded types. /w3tcompact/icons/smile.gif

 

[MChalkley]

Also, you'll note that I erroneously used the expression 'Grade 3' in my earlier posts. Technically, by SAE standards, there's no such thing, but unmarked bolts are often called Grade 3 in stores, for some reason.

Mark

 

[MChalkley]

Wen, I think I like your designations better. Let's call them half-hard, hard, and "huh?" from now on. /w3tcompact/icons/laugh.gif

Mark

 

[Djwalker]

On my mower I have a shear pin and I typically blow through 3-4 a year in mowing the pasture. On my auger I finally bought a slip clutch. Our soil has a real rocky layer (3" - 6" rocks) about 18" down and it wasn't uncommon to lose 3 or 4 pins per hole. With the clutch I just back off and start again. So, I think it depends on your conditions. If you don't break pins much I would stick with them because they are much cheaper. If you spend all of your time changing bolts I would get a clutch.

Dave

 

[W5FL]

Yeah, I personally would NOT have an auger without a slip clutch. I have the same problem with chunk rock soil (as well as solid rock). I find that most people with slip clutches don't know that they must maintain them properly or they would be MUCH better off with a shear pin. /w3tcompact/icons/smile.gif

 

[Bird]

JerryG, when I bought my first two Bush Hog implements, the dealer didn't have any shear pins in stock and wasn't sure which grade should be used, so I called Bush Hog and they just mailed me some spares.

Bird

 

[John Weaver]

Thanks for all the information. I bought the Bush Hog SQ600 with shear bolt arrangement. Used it about an hour, works great. Could have cut longer, but I read the instruction manual first (really). Looking at the shear bolt, it is in a collar that will allow it to spin free if the bolt breaks. I don't see what keeps the PTO drive shaft attached to the bush hog once the bolt breaks. It seems that the teliscoping action of the drive shaft could allow the drive shaft to come off of the splined attachment at the bush hog end. Is this possible? Normal?