Flail mower shear bolt — 12.9?

[LD1]

That's indeed a shear bolt. You can see the Shear bolt style yoke of the PTO shaft in the back.

Looks like this:

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No idea how a 12.9 grade bolt ended up there but it's not correct at all unless it will be powered by tractor with a lot of HP. Should be a grade 4.8 or 5.8 at max.

Keener eyes than mine to pick that up.

In any case....this is a NEW flail mower. Probably under warranty. And I didnt see any mention of problems or breaking a shear bolt....

What does the manual say? What does the warranting dealer say?

 

[ruffdog]

Does the manufacturer install that grade bolt if there is a clutch installed? There is no way I would install that high grade bolt. I would get a 5/16" (same as 8mm) grade 5 bolt and use that.

 

[ovrszd]

Since I couldn't remember, I went to the machine shed and checked my old Ford 917L flail mower. It doesn't have any shear protection or slip clutch. The gear box shaft is splined. The PTO shaft is splined on each end.

As LD1 mentioned, Flails are belt driven as is mine. They also use swinging cutters that will deflect when hitting a fixed object. So, in my case, Ford decided it didn't need any protection.

I'm wondering if the bolt in question is used to disconnect the PTO shaft, rather than provide protection?

Curious to hear the answer. If we knew the brand/model, we could investigate this more thoroughly.

 

[Tinhack]

Is it belt driven? If it is, it probably doesn't need a shear bolt and that's why it came with a 12.9 from the factory. My flail is driven by three monster belts, and even they slip--Especially when it found about 100ft of old barbwire. My flail doesn't even have a provision for a shear bolt.

 

[ovrszd]

Is it belt driven? If it is, it probably doesn't need a shear bolt and that's why it came with a 12.9 from the factory. My flail is driven by three monster belts, and even they slip--Especially when it found about 100ft of old barbwire. My flail doesn't even have a provision for a shear bolt.

neither does mine.

 

[S854]

PTSG, that’s my shear bolt…

I have a Betstco 60" Medium Duty Flail Mower, FH-EFG155… belt Driven… going to go on the back of my Kioti CK2610 HST…

I purchased it just before Christmas … I assembled it a few days ago and have been familiarizing myself with its workings… which is how I discovered this shear bolt…

Yes, the belts would probably slip if I pick up something in the field which would lodge in the rotor and keep it from turning…

I tend to take into account “worst case scenarios“… implement gearbox failure, PTO U-joint failure etc… so I’m gonna start with a grade 2 bolt and work from there if necessary…

 

[ovrszd]

That's a very good plan!!!

 

[S854]

Is it belt driven? If it is, it probably doesn't need a shear bolt and that's why it came with a 12.9 from the factory. My flail is driven by three monster belts, and even they slip--Especially when it found about 100ft of old barbwire. My flail doesn't even have a provision for a shear bolt.

I’m relatively new to tractors and an absolute novice when it comes to PTO shafts…

Is there such thing as a “solid” PTO shaft? (I.e. a U-joint on each end but with no provision for a shear bolt/slip clutch anywhere along its length…)

 

[ovrszd]

I’m relatively new to tractors and an absolute novice when it comes to PTO shafts…

Is there such thing as a “solid” PTO shaft? (I.e. a U-joint on each end but with no provision for a shear bolt/slip clutch anywhere along its length…)

Yes. I mentioned that earlier on my Ford 917L Flail Mower. Has a 6 spline shaft on the gearbox. Have a 6 spline shaft on the tractor. The PTO shaft is built with a slip in the middle.

 

[LouNY]

PTO shafts are available in a multitude of configurations with and without shear bolts.
For an interesting read you can browse this catalog,Bare Co USA - P.T.O. INDEX