Bush Hog BH25 yokes breaking

[RickB]

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

OK. You are there, I'm not. I don't think reinforcing those bars is the answer, but again, it's not my machine and I'm not there. While you have the welder out, weld those flex link halves together.

 

[Boatman62]

And this is what is being mowed.

As I said before, was looking to see if anybody had problems with these bars being compromised before being put into service.

 

[ning]

So this picture you provided

on the red link above, it looks like part is broken to the right.

If that part had another bolt hole for the black link to bolt through, then there would be zero flex in the system, so I'm ruling that out.

Instead, that part was longer to block the flex motion (keeping the black link below the red link) causing the black link's rotation upwards to force the red link upwards as well.

Now, with the part broken like that, the black link may be able to flex upwards enough, such that the black link is in line with the red link, whereupon there would be no tendency for the red link to rotate, and instead all of the force of the upward riding cutter would go straight through the links to the attaching bolts, and something gives.

If you'll excuse poorly-drawn scrawl on paper I've tried to illustrate this:

If the red link was better lubed, the red link may continue rotating with the black link and nothing bad may happen, but if the red link doesn't readily move then the black link more easily "catches up" with the red link and comes in line with it, causing the linear compression.

In fact I just found a picture from this manual :

Here you can see that the black links on the mower in question (orange & leading to the lower left in this pic) are supposed to be inside that upper link, and that upper link is supposed to be longer and have a bolt through... which will do what I described above.

Some of the pictures in that manual show the main triangle having 3 bolt holes; if this one's got 3, the flex link should be in the middle hole to allow more flexion.

Fix the flex link, and it'll work within a reasonable range of motion.
Or, leave it how it is, and use chains instead of the black links.

Either way, I'm with BH and the dealer on this one; operator error (in this case, a failed fix) caused those arms to break.

 

[JWR]

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.

Ah, I see what you are saying. The two bolts are not parallel which is because the left strap in broken and hanging lower than the right ... which is also why the left half of the flex link/clevis is lower as well.

Appreciate the positive feedback on the owner and, while I sensed a wreck of some sort, I did not mean to say he was necessarily that hard on his equipment.

 

[ning]

So this picture you provided
View attachment 721180

on the red link above, it looks like part is broken to the right.

If that part had another bolt hole for the black link to bolt through, then there would be zero flex in the system, so I'm ruling that out.

Instead, that part was longer to block the flex motion (keeping the black link below the red link) causing the black link's rotation upwards to force the red link upwards as well.

Now, with the part broken like that, the black link may be able to flex upwards enough, such that the black link is in line with the red link, whereupon there would be no tendency for the red link to rotate, and instead all of the force of the upward riding cutter would go straight through the links to the attaching bolts, and something gives.

If you'll excuse poorly-drawn scrawl on paper I've tried to illustrate this:
View attachment 721182

If the red link was better lubed, the red link may continue rotating with the black link and nothing bad may happen, but if the red link doesn't readily move then the black link more easily "catches up" with the red link and comes in line with it, causing the linear compression.

In fact I just found a picture from this manual :
View attachment 721187
Here you can see that the black links on the mower in question (orange & leading to the lower left in this pic) are supposed to be inside that upper link, and that upper link is supposed to be longer and have a bolt through... which will do what I described above.

Some of the pictures in that manual show the main triangle having 3 bolt holes; if this one's got 3, the flex link should be in the middle hole to allow more flexion.

Fix the flex link, and it'll work within a reasonable range of motion.
Or, leave it how it is, and use chains instead of the black links.

Either way, I'm with BH and the dealer on this one; operator error (in this case, a failed fix) caused those arms to break.

I see now that that same manual shows other pictures which are pretty similar to his pictures.

I'm standing by the assertion that the two links (black & the supposedly flexing orange yoke) are coming into line and causing a compression that's making the break. I guess that what looks like a break in the yoke is just wear & tear?

It just looks like a bad design now. Leaving my other post up just because...

 

[JWR]

Ning -- lots of good effort to explain but I disagree in a couple of places. First the photos you show from a manual or wherever are NOT of a BH25, that is some less heavy duty hog. Current pics of the BH25 do show the flex link/clevis halves on the inside and the straps on the outside just as the OP shows. I see you caught that too by your post #55. Second the OP will have to confirm but I do NOT see anything broken about the flex link/clevis. Some wear yes, broken no.

Also my studying of that linkage says there is no possibility of the black and red metal coming into straight alignment for compression. Take all cases into account and realizing the front one of the two relevant bolts is in a slot in the black metal, not a hole. Incremental movement tending toward compression from any position causes upward movement of the joint and prevents 'hard' compression. Not a faulty design there.


To the OP: Beautiful fields. Rarely do I get to bush hog on that nice a land/scene. Nothing there looks like trouble for rotary cutting.

 

[wirlybird]

Here is something to possibly look at. See the wear spot indicated by the arrow.
Could it be that the leading edge of the black bars are moving forward in the slot on the red part and binding at the front were the arrow points and not allowing the red part to pivot up?
I think I would get the tractor and cutter on to solid level ground with the 3-point lowered all the way as if cutting and then place a jack under the tail wheel boom and start to jack it up and see how the whole assembly works and pivots. See how far the rear wheel will go up before it runs out of travel and see if the bars start to bend outward.

 

[ning]

Also my studying of that linkage says there is no possibility of the black and red metal coming into straight alignment for compression. Take all cases into account and realizing the front one of the two relevant bolts is in a slot in the black metal, not a hole. Incremental movement tending toward compression from any position causes upward movement of the joint and prevents 'hard' compression. Not a faulty design there.

I think with extension, it could come into line, and then subsequent reversal could potentially cause the compression. If the other links are stiff, more easily than otherwise, and it won't necessarily happen every time. With more wear, though, the extension could result in a locked joint which would increase the chance of the compression.

If the flex yoke can't rotate downwards from its current position, I agree with you that extension causing the links to line up won't happen.

If you look at the wear inside of the black links, it does look like the red yoke is getting all the way in there at least occasionally.
Also note that it looks like the end of the red yoke is worn by impact with something - probably that angle is in place there intended to deflect the yoke upwards in case of a linear bind, but as that wear occurs, more and more strain is sent through the links briefly during the bind-up, and at some point there may be no more deflection from this angle and instead all of the strain may be going through the bolt on the left if the bolt on the right isn't hitting that ramp.

(apologies for lousy annotations but my screenshot extension doesn't have other colors)

 

[wirlybird]

Here is an actual picture from the manual showing the bends in the yoke straps. You can see how far back the bends are.
I think the straps on it are incorrect.
I would also check that the top link is getting set correctly as instructed in the manual.

Looks like part # 50050342

 

[Boatman62]

Here is an actual picture from the manual showing the bends in the yoke straps. You can see how far back the bends are.
I think the straps on it are incorrect.
I would also check that the top link is getting set correctly as instructed in the manual.

Looks like part # 50050342

View attachment 721193

Except I just unwrapped then new parts and helped him install them ..... new parts had a tag with that exact part number. I double checked.