Grade 8 'shear-bolt' on cutter

[hsvhobbit]

Got home friday and my step-son told me he broke the shear bolt on my Rhino SE6 cutter. HUMMM thinks I, the cutter's got a slipclutch on it and it's not supposed to HAVE a shear bolt. He shows me the bolt head and darned if it didn't have those 5 star points on it, yup, grade 8...

Now, I haven't been a good boy and loosened up the slipclutch and let it spin like I'm supposed to so maybe it froze up on me. While replacing the bolt we loosened it up and it spun under hand pressure, sure didn't seem to be rusted or frozen.

Not sure just what's going on there. Any hints? (oh yeah, the springs were compressed pretty much just like the spec said they should be)

 

[deereguy]

How did it shear? Did he hit anything?
It takes a heck of an object to shear a grade 8 bolt.

 

[hsvhobbit]

Says that all he hit was a clump of grass. I figure it had to be a cumulative thing on the bolt because the area of the property he was cutting has no big rocks, no stumps, nothing to even give pause to a riding mower, let alone a cutter.

 

[JerryG]

Normally I go by the manuals on equipment, but this is one instance where I don't. Instead of doing it the way the manual says to, I tighten the bolts until the springs are compressed a small amount while keeping the amount the same between all bolts. Then I try it out in thick grass. If it slips, then I will tighten them one turn each. Usually I have to stop twice to get the adjustment that I want.

 

[heymack]

My cutter calls for a Grade 2 bolt. Well when I sheared the first bolt, I went down to the dealer looking for a Grade 2 replacement. All they had were 5's and the parts guys said that's all anybody uses. I installed the Grade 5, but kept an eye out for some 2's. When I found the correct bolts, I replaced the 5 with a 2 (month or so later). Much to my surprise the 5 was bent to heck but not broken. It was evident that the bolt took some pretty hard knocks when hitting rocks and stumps. I don't believe I did any damage to the unit, but will only be running 2's from now on.

 

[Birdhunter1]

How big of a bolt is it?

I used to have an old Bushhog that called for a grade 8 bolt as the shear pin, but it was a 5/16" bolt. My current bushhog takes a 1/2" grade 2 bolt.

 

[heymack]

How big of a bolt is it?

I used to have an old Bushhog that called for a grade 8 bolt as the shear pin, but it was a 5/16" bolt. My current bushhog takes a 1/2" grade 2 bolt.

Mine takes 1/2" x 3" bolts.

 

[Farmwithjunk]

Slip clutches will "freeze" (rust) to a point where they won't slip even if adjusted properly. They need to be forced to slip and slipped enough to "shine" the mating surfaces. A mower equipped with a slip clutch that is stored outside will most likely need the treatment more often than one kept out of the weather, but none-the-less, I do it with my mowers AT LEAST twice per season.

On the shear bolt... Is (was) the bolt that sheared of proper size? (Still, it SHOULDN'T have been grade 8, even with a slip clutch) Too small of a diameter bolt will shear with quite a bit less resistance than a properly fit bolt.

Heavy grass can offer up quite a bit loading on a mower. I've waded into a tall stand of bermuda grass before that stopped a 60+hp tractor with a 6' cutter, almost dead in its tracks. The only thing that kept it from killing the motor was when the slip clutch went up in smoke.

 

[MarkV]

Is it possible that the shear bolt was replaced by the factory or dealer with a grade 8 because the mower was being shipped with a slip clutch? Of course that would not explain why it sheared unless the slip clutch was frozen.

MarkV

 

[Dieselmh]

How many hours are on that mower? It may have failed due to age and abuse over time. Kind of like "the straw that broke the camel's back" kind of thing. Hours and hours of stress on a bolt will eventually break it, slip clutch or not.