Newbie PTO Question - Sheared Pin

[mculik5]

Hi.

New Kubota B2650 owner (since October 2020). Earlier today, I was using an aerator/slit seeder (old Olathe 37/38) I purchased to renovate my lawn. Things were going great until I caught a rock that got stuck in the aerator and caused the PTO shaft shear bolt to shear. Fortunately, no damage and I got the rock out without too much hassle.

Setup background:

- The PTO shaft is an old, unguarded tri-lobe. I believe the brand is Eurocardan based on the logo, yellow paint and tri-lobe, but not 100% sure. Regardless, the U-joints are tight, it slides freely and the connector button operates nicely.

- The only place to put a shear bolt through the shaft is on the implement end.

- The shear bolt hole appears to be threaded. Looks like a fine thread. 5/16 bolt fits without threading and a 3/8 bolt doesn't fit. M8 bolt also fits without threading. I don't have a M9 bolt to test.

- Both the shaft and aerator gearbox input have keyways in addition to the shear pin holes.

A few questions:

1. Is a key used in addition to the shear pin? I know it had a shear bolt, but not sure about a key, as I never removed the shaft before using it.

2. Does anyone know the specs for the replacement shear bolt? Diameter? Thread? Breaking force?

3. I always thought shear bolts had a non-threaded shoulder. Are there also fully-threaded styles?

Thanks in advance!

 

[BigG]

Put the 5/16 bolt all the way thru it and put a nut on the outside. You do not want a bolt to thread into the hole. How would you get the broken piece out of the hole? Unless it was a bolt threaded all the way up and you put the head of the bolt on the threaded side. But this is still not a good idea.

 

[Russell King]

No key with a shear pin. I assume that a key may be required if you use a slip disc in place of the shear pin.

 

[UpNorthMI]

Use 5/16 and nyloc. The bolt should be low or no grade. Better to change bolt than damage anything else.

I have a similar set up on a toro leaf blower, just buy a bag of cheap bolts.

 

[mculik5]

@BigG, @Russell King, @UpNorthMI - Thanks!

You're all saying what I was thinking. Will check my local stores for Grade 2 bolts tomorrow.

Interestingly, the lowest grade McMaster has is 5. I see lots of 1/2" OD shear bolts online, but none 5/16". Any sources?

 

[NCL4701]

By all means use a soft bolt if you don’t know the actual spec, but if you can find a manual for the implement, check the spec for the shear bolt.

We used to shear bolts on the Howse 500 rotary cutter pretty often until we downloaded the owner manual and saw it specifies a Grade 5. A lot less shearing going on now. Bought it used many years ago and didn’t have the manual for the first decade or so.

 

[JimmyJazz]

They sell shear bolts at Tractor Supply. I have bought more than my share. Good luck.

 

[UpNorthMI]

There does not appear to be a 5/8" commercial shear bolt for PTO shafts, at least I will say that I could not find them, there are lots of snowblower shorter shear bolts of this diameter. In the end it is just trial and error to find a bolt that works for you without it regularly shearing too often. If it shears too often for no valid reason then I agree with NCL 4701 try moving up to a grade 5 bolt.

The only attachment I have this size shear bolt on is an old Toro 2613 Debris Blower. As I go back and look at a manual that I recently found it shows a Ratchet Torque Limiter on the attachment end of the PTO shaft part diagram. I purchased this old blower used and it did not come with a pto shaft. The input shaft on the blower was 1.5" diameter and had a small hole through it, I guess in reality I don't have the correct PTO shaft setup as per the setup when the blower was new. Maybe the OP has the same issue with his old attachment.

If I'm careful with clutching in the PTO on the blower I have no issue with it, it gets used a couple of times a year on the back of my L3200, maybe I will try a grade 5 bolt next time. I'm certainly not buying a new PTO shaft with a ratchet torque limiter for it! Original parts are no longer available and I have no clue about the strength of torque required for this unit.

Better to shear the bolt than anything else!!!