PTO Shaft to Gearbox Bolts Keep Breaking!

[airbiscuit]

I'm wondering if it's a combination of variables:

1. The hole in the collar or shaft is slightly oversized or wallowed
2. The bolt isn't long enough (collar rests on threads)
3. The bold isn't tight enough - allowing it to spin and degrade
4. There is some unusual vibration at the gearbox
5. There are demons at play

First I would use a longer bolt (so no threads in the collar), use a lock washer and tighten it tight. Maybe wrap the nut end with duct tape so you can retrieve it if it fails.

If that fails, see if a 14mm bolt will fit in there snugly.

 

[SPYDERLK]

Using a 6** type Loctite and a grade 8 bolt would stop this problem. Heat would be needed to get it apart later.

Unless you unfortunately happen to use #620, which is strong up to 232C. This formulation is one of the strongest to start with, and gets stronger as it ages at mild heat. Youll be melting seals and blueing bearings to get this one off.

-- #638 would be a good choice. Highest strength but loses almost 50% by 100C.

 

[wirlybird]

Nothing new to report as I have been very busy in between storms mowing.

Idea: What do you guys think about using a "pin", something like you'd use on a toplink instead of a bolt to join the PTO shaft to the gearbox? This could give a uniform diameter all the way through. I know, just use a longer bolt, but I was wondering about why not a pin?
I haven't looked yet but I'm sure I could get a grade 5 or 8 pin. I'm not sure what the downside might be yet.

 

[airbiscuit]

I still think, use a longer bolt tightened down firmly, or a slightly larger (14mm) bolt that will be more snug. You don't want a pin spinning around in there wallowing out the holes.

 

[ning]

Nothing new to report as I have been very busy in between storms mowing.

Idea: What do you guys think about using a "pin", something like you'd use on a toplink instead of a bolt to join the PTO shaft to the gearbox? This could give a uniform diameter all the way through. I know, just use a longer bolt, but I was wondering about why not a pin?
I haven't looked yet but I'm sure I could get a grade 5 or 8 pin. I'm not sure what the downside might be yet.

My guess is that a bolt is much cheaper than a "pin", and is a presumably known quantity as for shear value (grade 2/5/8 etc) vs the pin being whatever it is.

 

[DarkBlack]

Another vote for staying with bolts.

Wrap some duct tape around the pto shaft - bolt/nut assembly so it doesn’t fall out when it breaks
This should help with the big mystery of how it can break off only one side.
With duct tape wrapped a few times around everything, you will need to end up with 3 pieces for the pto shaft to loose drive

 

[wirlybird]

My guess is that a bolt is much cheaper than a "pin", and is a presumably known quantity as for shear value (grade 2/5/8 etc) vs the pin being whatever it is.

I am sure on cost a bolt is cheaper. If I did try a pin I'd make sure to order one that is a specific grade such as 5. Haven't looked yet.
I may try it just to see how it goes.

 

[ning]

I am sure on cost a bolt is cheaper. If I did try a pin I'd make sure to order one that is a specific grade such as 5. Haven't looked yet.
I may try it just to see how it goes.

Only advantage I can see is how trivial it is to put the lynch pin in to hold it.

That brings up another disadvantage - there will potentially be some shear -- probably not much but non-zero -- on the lynch pin holding the main pin, and who knows what those are made of. Of course you can use a bolt and nut there... with a washer... ok now we're way beyond the cost of just a bolt.

 

[airbiscuit]

I still think, use a longer bolt tightened down firmly, or a slightly larger (14mm) bolt that will be more snug. You don't want a pin spinning around in there wallowing out the holes.

Another vote for staying with bolts.
Wrap some duct tape around the pto shaft - bolt/nut assembly so it doesn’t fall out when it breaks
This should help with the big mystery of how it can break off only one side.
With duct tape wrapped a few times around everything, you will need to end up with 3 pieces for the pto shaft to loose drive

Why do you seem to prefer a pin to a bolt?

 

[DarkBlack]

Why do you seem to prefer a pin to a bolt?

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