PTO Shaft to Gearbox Bolts Keep Breaking!

[wirlybird]

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

It was just a thought.
Main idea is a constant diameter of the pin, no threads.
When you're out doing a 15 acre field with no obstacles you get time to think of things!

 

[wirlybird]

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.

Yea, I was thinking a small bolt.
Anyway, it was just an idea.

 

[old and tired]

Taking another stab at this.

The PTO only breaks the threaded side of the bolt.

My guess (correct me if I'm wrong) you would pull out the broken bolt and insert another bolt in the same direction (yes? or no?).

Try inserting the bolt in the opposite direction, if it still breaks the threaded side, I'm at a loss...

Are you still breaking them?

 

[SPYDERLK]

Taking another stab at this.

The PTO only breaks the threaded side of the bolt.

My guess (correct me if I'm wrong) you would pull out the broken bolt and insert another bolt in the same direction (yes? or no?).

Try inserting the bolt in the opposite direction, if it still breaks the threaded side, I'm at a loss...

Are you still breaking them?

I dont think he has ever sheared the longer bolt he put in that has a shank spanning both shear points. ???

 

[airbiscuit]

I'm not sure he ever tried a longer bolt, a bigger bolt (14mm), or duct tape around it to preserve the evidence. Until that happens, these are just theoretical solutions.

 

[SPYDERLK]

I had put a longer bolt in it and it has about an hour or so on it.
Going to take a look once the storms pass.
Thing is though I use the 1/2 by 3 bolts on all of my cutters and this is the only one having issues!
May also swap out the shaft and see what happens.

I dont think he has ever sheared the longer bolt he put in that has a shank spanning both shear points. ???

I'm not sure he ever tried a longer bolt, a bigger bolt (14mm), or duct tape around it to preserve the evidence. Until that happens, these are just theoretical solutions.

Yup. The problem is fatigue at the stress riser in the thread root.
- The longer bolt should do it.

 

[wirlybird]

Yup. The problem is fatigue at the stress riser in the thread root.
- The longer bolt should do it.

Yes, longer bolt seems to be doing better.
Going to pull it when I get time to see how it looks.

 

[Travis_R]

wirly bird,

Did you ever find out what the problem was?

 

[airbiscuit]

Yes, longer bolt seems to be doing better.
Going to pull it when I get time to see how it looks.

Maybe the longer bolt worked

 

[wirlybird]

Longer bolt is holding up so far. Been busy so not much time to look at it!

 

[Maka]

I had an Iron Craft customer breaking shear pins and found he was buying grade 2 from harbor freight. We put the OEM bolts in and no problem after that.

 

[wirlybird]

I had an Iron Craft customer breaking shear pins and found he was buying grade 2 from harbor freight. We put the OEM bolts in and no problem after that.

Well, since a "shear pin" is a grade 2 bolt was the issue the Harbor Freight bolt specifically?

 

[ning]

Well, since a "shear pin" is a grade 2 bolt was the issue the Harbor Freight bolt specifically?

Some units call for a grade 5 pin/bolt.
I'd expect if the grade 2 were consistently breaking, the situation called for grade 5.
Best to check the manual / manufacturer.

 

[SPYDERLK]

Some units call for a grade 5 pin/bolt.
I'd expect if the grade 2 were consistently breaking, the situation called for grade 5.
Best to check the manual / manufacturer.

Every double shear situation calls for having the bolt shank across both shear lines.

 

[wirlybird]

Some units call for a grade 5 pin/bolt.
I'd expect if the grade 2 were consistently breaking, the situation called for grade 5.
Best to check the manual / manufacturer.

I currently run 7 brush hogs of different makes and models and not one manual calls for a grade 5.

If grade 2 bolts are constantly being broken then my first thought is the cutter is not set up correctly, cutting too low for the terrain and/or frequently hitting or running over stuff it shouldn't be.

 

[ning]

I currently run 7 brush hogs of different makes and models and not one manual calls for a grade 5.

If grade 2 bolts are constantly being broken then my first thought is the cutter is not set up correctly, cutting too low for the terrain and/or frequently hitting or running over stuff it shouldn't be.

That's great!
(insert "big thumbs up" meme here)

I also don't have any equipment with grade 5 shear requirements, but they do exist.
Not everyone's equipment is the same, and you're not the only one reading this.

 

[SPYDERLK]

I currently run 7 brush hogs of different makes and models and not one manual calls for a grade 5.

If grade 2 bolts are constantly being broken then my first thought is the cutter is not set up correctly, cutting too low for the terrain and/or frequently hitting or running over stuff it shouldn't be.

Hmm. I have a Woods HC-60 that came used "like new" with a 1/2" Gr5 shearbolt. We have sheared 2 of them. -- Not myself. I only did the replacing. The shank crosses the 2nd shearline comfortably. I dont know the circumstances that sheared them. Im surprised that much torque can be applied to 5' bushog having a stump jumper. Maybe somebody is engaging the PTO WFO and not owning up.

 

[RayIN]

I use gr 2 bolts. I want the part that breaks to be the easiest to replace, and the cheapest. I usually break 1 bolt every time I use my KK rotary mower. Seems like there is a fallen tree limb hidden down in the grass every time. I carry 2 spares in the tractor toolbox all the time.
I can be back up and mowing in 15 minutes. If the yoke breaks instead of the bolt, it gets expensive, in both time and money.

 

[Maka]

Well, since a "shear pin" is a grade 2 bolt was the issue the Harbor Freight bolt specifically?

We used grade 2 from Iron Craft and no problems.

 

[Maka]

Well, since a "shear pin" is a grade 2 bolt was the issue the Harbor Freight bolt specifically?

I think yes, the problem was they were Harbor Freight. He brought it to us and the bolts he was using and they broke when engaging the PTO at as it should be. We put in OEM bolts and zero problem. Its been a month now and he has come in several times for other things and he has not broken one of the OEM bolts.