Shear pin?

[BMW]

A buddy of mine gave me an old Woods Cadet 60 rotary mower. I tightened up the spindel to take up the slop in the bearings and it works fine now. What should I use for a shear pin? It just has a 1/4" bolt (I didn't check what grade).

 

[kadonte]

grade 8

 

[Anonymous Poster]

Most all shear pins are Grade 2

Confirm with a Woods dealer to prevent any damage.

 

[Boondox]

Wow! Maybe this depends on the manufacturer? All the shear bolts on my King Kutter and Woods implements are grade 5. Had a friend with a Woods snowblower who got tired of replacing the grade 5s and replaced it with an 8. Next hunk of firewood he hit tore his blower all to h*%@.

Best advice I can offer is to check with the manufacturer.

Pete
www.gatewaytovermont.com

 

[DaveNH]

And a cheap grade two at that!
When one breaks, buy two!

We're all in this together! (3)
Executive Yuppie Tractor Owner

 

[kadonte]

shear pins rely on "brittle", not bend. Grade 2 will do a good job of elongating pin holes.

 

[kadonte]

I defer...preferred use is probably a grade 5. I have luck and less problems using the 8's. I would not want to steer someone in a wrong direction based on my usage of a particular grade of bolt.

 

[hayden]

I just checked the manual/parts list for my woods 4" mower. The manual covers the larger models too.

In BIG BOLD type is says to use only grade 2 bolts for the shear bolts.

My snow blower also calls for grade 2.

I strongly suggest NOT using grade 5 or higher. The softer bolts are used on purpose - so they shear under stress. I blow out one or two every time I use my snow blower because I keep picking up rocks. When I first blew one out, I didn't have a grade 2 replacement so I used a grade 5. Next rock I caught blew out the #50 drive chain. Now I only use grade 2 and I buy them a half dozen at a time.

If you find you are breaking them frequently, as I am, switch to a slip clutch. That's what I plan to do this summer. Changing the shear bolts is getting old - but it still beats replacing the gear box or chain.

Peter

 

[Keoke]

Peter, the best setup is a combination of shear bolt and clutch pak; with clutch set to slip just before bolt shears. The down side of clutch paks is that they tend to rust up locking up the drive to driven plates together when they sit for a time. The shear bolt would protect unit against this. In use, if you shear the bolt then it is time to unstick the clutch pak. I use two pipe wrenches to break the clutch loose when they lock up.

george

 

[Jag]

George... WD40

 

[Von]

Jag, I don't think you want to spray oil on any dry clutch. It would cause the clutch to not grip therefore slipping and in effect not work.

 

[GlueGuy]

BMW,

Go with John's advice, use the grade 2 bolts. You want the bolts to blow, not your equipment. Kinda like a circuit breaker in an electrical circuit: you want the fuse to blow before the wires melt (or catch fire /w3tcompact/icons/shocked.gif!!!).


The GlueGuy

 

[Bird]

<font color=blue>Go with John's advice, use the grade 2 bolts.</font color=blue>

Amen!

Bird

 

[MarkJC]

Just so everyone is clear, a grade 5 bolt has 2 lines on it. A grade 8 bolt has 5 lines on the head strike. A bolt without lines on the head strike is buyer beware, you don't know what you're getting, but it's probably soft, so it would have a lower shear strength than a higher grade bolt. The difference in grading primarily relates to tensile and shear strength and is derived from different alloys and heat treat processes. A properly designed shear pin protected drive train should have the shear pin fail as the first line of defense to damage, using a higher shear strength bolt puts the whole thing at risk for damage.

 

[Jag]

Von, just a light shot to keep the rust away... What is best, slip to soon or slip to late...

 

[TWINKLE_TOES]

Just to make it clear'er/w3tcompact/icons/smile.gif

<font color=blue>a grade 5 bolt has 2 lines on it. A grade 8 bolt has 5 lines on the head </font color=blue>

This is from Thomas J. Glover, pocket reference on bolt grades.

SAE Grade 0 -1-2 no lines
SAE Grade 0 -1-2 no lines
SAE Grade 0 -1-2 no lines
SAE Grade 3 two lines
SAE Grade 5 three lines
SAE Grade 6 four lines
SAE Grade 7 five lines
SAE Grade 8 six lines

Please note that just because a bolt is grade 2 does not mean
it will break easily. Grading only refers to the minimum strength, not the maximum. Thus, if a machine uses a soft bolt as a safety shear pin, and you happen to replace it with a grade 2 bolt that was actually manufactured to grade 8 specs (but was marked down because too many of the bolts in the lot failed, so the whole lot was marked down) you could create some serious problems. Replace safety-related items
with proper stuff! Also beware of improperly-marked forgeries.

Al

 

[Von]

Jag,
But what if you now have constant slipping and have to buy new clutch packs? I still say no oil on dry clutchs with no exceptions! Unless you have money to burn on new parts every year. You are better off removing the pressure on the clutch pack so that rust will not be a problem.

 

[hayden]

Or for those of us who are memory impared - the grade is the number of lines plus 2.

 

[ddl]

Question: Is not the bolt markings molded into the bolt head when the formed? If so, how can a grade 8 be changed to grade two when bolt fails specs? Am I missing something?

Dan L

 

[RJohnson]

The grade designation comes from the automotive industry, their specification SAE-J429. There are ASTM standard bolting specifications that have compairable bolts. The problem with the two standards is that the marking requirements are different. An SAE Grade 2 for example has no markings, it also has two different strenght levels depanding upon the diameter of the the bolt. For 1/4 through 3/4 the bolt has a 74,000 psi tensile strength as a minimum, over 3/4 through 1 1/2 the tensile strength drops to 60,000 psi. The ASTM A307 is a compairable bolt (with no markings) but its minimum tensile strength is 60,000 psi no matter what the diameter. This is exactly like MarkJC stated, you don't know what you are getting and with a minimum tensile strength specification you can end up with bolts of the same grade with drastically different mechanical properties. I am going to scan a bolt head identification chart and will try and post it tomorrow.

Randy