Bush Hog BH25 yokes breaking

[JWR]

I see torch marks on the back end of that toggle/flex link and there shouldn't be any. Has it been shortened enough so it aligns with the failing bars? If they are aligned and parallel in tension the link won't work as designed in compression.
The fore/aft centerline of that flex link needs to be at a lesser angle from horizontal than the center line of the black bars.

Not so sure those are torch marks (?) That part of the flex link is meant to be limited in downward travel in order to prevent a fold "under" instead of fold over the pivot bolt. The ragged edge may be the result of banging on the bolt ?

 

[wirlybird]

I still think the problem is coming from backing into stuff and forcing the cutter up with too much force.
Looking at pictures of the original set up of the BH25 I think the two bars are not the same.
The "bend" in the bars is much closer to the rear mounting tabs in the pictures of a new one.
The bend in the bars on his is much further toward the front of the cutter. You can see in the picture that it seem to contact the rear mounting tab at a bit of an angle which could create a binding point.

ing point.

 

[RickB]

Not so sure those are torch marks (?) That part of the flex link is meant to be limited in downward travel in order to prevent a fold "under" instead of fold over the pivot bolt. The ragged edge may be the result of banging on the bolt ?

The paint is burnt on the edge. The end has obviously been flame cut. The bolt that the part strikes against would make a small mark on it. There would be no contact along the entire end. There is nothing there for the entire edge to hit.
The link is obviously not designed to fold under. It is also not designed to be parallel with the failing bars.
Rough ground or unique operating conditions can also demand more travel than the flex link can provide. Replacing the bars with chain is still an excellent alternative.

 

[JWR]

Wirlybird -- I agree for sure. That is the only mode in which I broke mine and I bet that's how all of them get broken -- backing too hard into something creating unpredictable upward motions. Great catch on noticing that 'kink' being down much closer to the rear attach points (yellow arrow) on the newer hogs ! I believe the 'natural' bending or kink point for failure mode is about mid length of those straps making that a poor place to put the manufactured kinks. That may well be why the newer ones are near the rear attach points.

 

[JWR]

The paint is burnt on the edge. The end has obviously been flame cut. The bolt that the part strikes against would make a small mark on it. There would be no contact along the entire end. There is nothing there for the entire edge to hit.
The link is obviously not designed to fold under. It is also not designed to be parallel with the failing bars.
Rough ground or unique operating conditions can also demand more travel than the flex link can provide. Replacing the bars with chain is still an excellent alternative.

You may be right, Rick. I saw what I thought was rotational wear and you saw it as burned paint. Your strongest evidence is the ragged edge which would tend toward a torch cut. But the whole clevis or flex link does not seem to be any shorter (based on the bolt positions in brand new machine pictures) so that is a puzzle if it was torch cut.

The more I look at the large pictures of the problem rig the more it looks to me like the whole thing was "in a wreck" of some sort. Notice that the right side strap up in/near the flex link/clevis is twisted from the vertical? How do you even do that ? I'm thinking that happened at the moment of the harsh rear end collision with a tree or boulder or whatever. When you back too hard into some obstacle the hog raises up under terrific stress goes into a twisting motion (counterclockwise when viewed facing forward) which snaps the left strap and leaves the right one twisted as the picture shows it. AND I'm with Bush Hog and the dealer saying "Nope, we don't cover that behavior and that result." Actually I could see this damage potentially having happened from the tractor running away backwards down a hill ending in a collision of the hog with some immovable object. NOT saying it did ...


p.s.: Rick, I think that the most forward bolt in the flex link/clevis (one that says YfS on the bolt head) is in a slotted hole in the black center metal. Thus repeated (errant) contact between the red parts you see as having been torch cut can be all along those red metal edges for a distance equal to the length of the slot in the black center metal. If so it was a lot of times ... more sign of abuse, if that was the case.

 

[RickB]

Additionally the flex link is supposed to be a welded assembly. In the pics it appears to be two separate pieces that can move independently. That's not at all helpful.

 

[Boatman62]

I see torch marks on the back end of that toggle/flex link and there shouldn't be any. Has it been shortened enough so it aligns with the failing bars? If they are aligned and parallel in tension the link won't work as designed in compression.
The fore/aft centerline of that flex link needs to be at a lesser angle from horizontal than the center line of the black bars.

There are no torch marks. Nothing has been modified or shortened. When that link is in the resting position, everything is in direct alignment. When upward pressure is applied to the tail wheel the ramp is forced upward by the rear bolt that has a bushing on it.

It's as it should be. There is some wear on that ramp but it's not affecting anything.

 

[Boatman62]

The pivot link allows only so much travel. Is he backing up to steep banks or something similar that would bottom out the link? Or operating with the link already well into its travel?

Even with the link bottomed out the 3pt should allow the deck to get pushed up. So there shouldn't be that much force through the bars, just some fraction of the weight of the mower. Clearly that's too much for that bend but it should be ok with some reinforcement.

Nothing steep.... there are a couple swails but nothing real steep.

 

[Boatman62]

Additionally the flex link is supposed to be a welded assembly. In the pics it appears to be two separate pieces that can move independently. That's not at all helpful.

Parts fische shows it as two separate parts not welded together. I have seen some that are welded but this one is not.

 

[Boatman62]

You may be right, Rick. I saw what I thought was rotational wear and you saw it as burned paint. Your strongest evidence is the ragged edge which would tend toward a torch cut. But the whole clevis or flex link does not seem to be any shorter (based on the bolt positions in brand new machine pictures) so that is a puzzle if it was torch cut.

The more I look at the large pictures of the problem rig the more it looks to me like the whole thing was "in a wreck" of some sort. Notice that the right side strap up in/near the flex link/clevis is twisted from the vertical? How do you even do that ? I'm thinking that happened at the moment of the harsh rear end collision with a tree or boulder or whatever. When you back too hard into some obstacle the hog raises up under terrific stress goes into a twisting motion (counterclockwise when viewed facing forward) which snaps the left strap and leaves the right one twisted as the picture shows it. AND I'm with Bush Hog and the dealer saying "Nope, we don't cover that behavior and that result." Actually I could see this damage potentially having happened from the tractor running away backwards down a hill ending in a collision of the hog with some immovable object. NOT saying it did ...


p.s.: Rick, I think that the most forward bolt in the flex link/clevis (one that says YfS on the bolt head) is in a slotted hole in the black center metal. Thus repeated (errant) contact between the red parts you see as having been torch cut can be all along those red metal edges for a distance equal to the length of the slot in the black center metal. If so it was a lot of times ... more sign of abuse, if that was the case.

NOTHING HAS BEEN CUT WITH TORCH.

What you are seeing as twisted is not. The broken bar on the left side is letting the yoke sag and making appearing to be twisted. It's not.

This guy doesn't abuse anything. In fact, pretty much everything I've been repairing for him is just because the equipment is sitting around unused. He was a test pilot for Lockheed back in the day and everything is strictly by the book. If the manual says don't exceed 2500rpm, he won't go over 2400rpm.