Broken casting on BH 77 excavator

[torch]

Welcome to the forum!
You were doing loader work over rough ground, by your description, for about 8 hours. With the pin in place, there would be a significant amount of leverage on that pin and the casting. From the looks of it, it's not a casting defect, but a failure due to overload. As suggested, the pin should not have been left in place. Whether Kubota will cover it, you'll have to ask.
I'm curious- in the owners manual, what is the instruction for using the pin?

Disclaimer: I have a different model Kubota backhoe, so this may not apply.

But in MY Kubota BH manual there is a large bold CAUTION notice clearly stating the swing lock should be engaged while driving around:

CAUTION:
Raise and center the boom, close the bucket and dipper, engage the swing and boom locks and disengage the tractor PTO, before transporting the backhoe around the jobsite.

I'd read the manual carefully before calling the dealer.

 

[beckmurph]

If you blow up the picture of the locking pin, there is paint and a chunk of metal missing.
Looks like something hit the bh boom real hard.

Check the left side of your backhoe to look for damage.

It could have been hit sitting on the dealers lot.

 

[GreensvilleJay]

THAT makes sense !! Hit the boom or bucket and a LOT of force goes to the pin !!
Never thought of that...
Note to self, remove swing pin....
next....maybe read the manual.... ?

after I deal with the dreaded loader coupler leak...

 

[TheOldHokie]

I just bought a new 3302 tractor with a BH77 excavator attached from dealer. I have only 8 hours on tractor, and have barely used the excavator. Yesterday this casting broke - its at the area where the safety pin is installed to keep excavator from swinging from right to left. Has this happened to anyone else? I have not abused the tractor in any way, in fact I am a new tractor owner and have been babying the heck out of it. Seems like a bad casting but wanted to see what anyone else thought? Thanks

I was curious - $980 retail for a replacement.

Dan

 

[Yooper]

That part doesn’t look like a casting. It looks like a formed plate which would mean it is mild steel plate. But your picture sure looks like a cast steel break. Scratching my head on this one

 

[GreensvilleJay]

Yike, I looked to.. that's $980 US$ about $1200 canucks.
it's a one piece casting. now it 'could' be replaced with a steel plate....

 

[TheOldHokie]

Yike, I looked to.. that's $980 US$ about $1200 canucks.
it's a one piece casting. now it 'could' be replaced with a steel plate....

That part doesn’t look like a casting. It looks like a formed plate which would mean it is mild steel plate. But your picture sure looks like a cast steel break. Scratching my head on this one

Looks like a casting to me.

Dan

 

[fried1765]

Next time remember to pull the pin before operating the swing

Precisely !

 

[Donystoy]

It is certainly a casting. Going to remove the pin on mine and put it in "storage". Not sure why it is needed as my old B/H did not have one. If it was mine, I would probably just cut it straight across and paint it.

 

[hagrid]

I, Spraynard, would prep the fractures and weld with 7018. Slowly, as to not overheat the upper pivot joint.

And cover the swing ram to prevent spatter damage.

 

[TheOldHokie]

I, Spraynard, would prep the fractures and weld with 7018. Slowly, as to not overheat the upper pivot joint.

And cover the swing ram to prevent spatter damage.

How about welding a reinforcing plate on top as well?

Dsn

 

[Donystoy]

I would think that to properly weld it with E7018 rod it would have to be completely dismantled so it can be pre-heated, similar to welding a cracked exhaust manifold. As previously stated, this feature is not even required.

 

[TheOldHokie]

I would think that to properly weld it with E7018 rod it would have to be completely dismantled so it can be pre-heated, similar to welding a cracked exhaust manifold. As previously stated, this feature is not even required.

Is this cast iron or steel? Cast iron seems like an unlikely choice.

Dan

 

[hagrid]

How about welding a reinforcing plate on top as well?

Dsn

Mmm... I see your point. I feel as if a piece of the puzzle is currently residing in the belly of a beagle.

The fractured material seems to be of significant heft, yet the fractures themselves show no sign of cyclical damage; the rupture happened during a single event. The fracture appears ductile therefore the material properties seem to be beyond reproach (allegedly, without further testing). Due to aforementioned heft, the force required for rupture would naturally have to be significant... something outside the realm of jostling during traversal of uneven terrain.

Without attempting to lay blame, i think the hoe knuckle was exposed to dramatically more force than was ever envisioned. THEREFORE... I would probably not reinforce the area and instead, endeavor to avoid exposing the repaired mechanism to unseemly loads.



lol... loads.

I would think that to properly weld it with E7018 rod it would have to be completely dismantled so it can be pre-heated, similar to welding a cracked exhaust manifold. As previously stated, this feature is not even required.

Where it concerns mild steel, which I think is the composition of the casting, I rarely preheat unless section thickness reaches biblical proportions. 7018 is a mild steel electrode.

Conversely, alloyed steels requiring a 10018 or 11018 electrode are sensitive to underbead cracking of the root pass. Preheat is a requirement as are interpass temperature limits.

Exhaust manifolds are usually cast iron and that is a zebra of a different stripe. I generally use a nickel-based electrode for those nightmares.

 

[TheOldHokie]

Mmm... I see your point. I feel as if a piece of the puzzle is currently residing in the belly of a beagle.

The fractured material seems to be of significant heft, yet the fractures themselves show no sign of cyclical damage; the rupture happened during a single event. The fracture appears ductile therefore the material properties seem to be beyond reproach (allegedly, without further testing). Due to aforementioned heft, the force required for rupture would naturally have to be significant... something outside the realm of jostling during traversal of uneven terrain.

Without attempting to lay blame, i think the hoe knuckle was exposed to dramatically more force than was ever envisioned. THEREFORE... I would probably not reinforce the area and instead, endeavor to avoid exposing the repaired mechanism to unseemly loads.



lol... loads.

Where it concerns mild steel, which I think is the composition of the casting, I rarely preheat unless section thickness reaches biblical proportions. 7018 is a mild steel electrode.

Conversely, alloyed steels requiring a 10018 or 11018 electrode are sensitive to underbead cracking of the root pass. Preheat is a requirement as are interpass temperature limits.

Exhaust manifolds are usually cast iron and that is a zebra of a different stripe. I generally use a nickel-based electrode for those nightmares.

That was very diplomatically phrased

Dan

 

[GreensvilleJay]

The easy repair is to cut an appropriately shaped 1/4" or 3/8" plate steel, drill 4 small holes,2 big ones. The 4 small mount the plate, big ones for the pin and pivot.
The welding repair could/would be 'tricky'....

 

[Alfred_2345]

I have a BH77 and being a newbie operator, I know I have tried to swing with the lock in place. Probably not at wide open throttle and I am sure I backed off as soon as it didn't move. I would think/expect that the design would be robust enough to handle an operator trying to operator the BH with the locks in place as it can be expected.

Now driving around with the pin in and hitting something with bucket could impart a high shock load.....

I know when I first got the tractor, I (lightly) hit a few things with the FEL. Now I have my head on a swivel whenever I am moving.

 

[JPM]

Thanks for all of the input - I appreciate it. The dealer specifically told me to always have the pin in when driving tractor around for safety reasons. He indicated that the boom can swing left or right and represent a crushing hazard. I agree with some who posted that the fracture is a brittle fracture and there are no obvious inclusions or excessive pores in casting that would cause problem. Having said that I dont know what kind of cast iron (Malleable, ductile, or what) it is and I didnt have a metallurgist look at it to see if maybe the chemistry is off such that it is weaker than was expected when they sized the casting. When I posted this I was wondering if others had problems - that would indicate a poorly designed, undersized component. No where in manual does it say not to leave pin in when the tractor is moving. My father in law and my father have Kubotas and love them. To say I am dissappointed is an understatement. Thanks again for all of the feedback, I really appreciate it.

 

[fried1765]

Thanks for all of the input - I appreciate it. The dealer specifically told me to always have the pin in when driving tractor around for safety reasons. He indicated that the boom can swing left or right and represent a crushing hazard. I agree with some who posted that the fracture is a brittle fracture and there are no obvious inclusions or excessive pores in casting that would cause problem. Having said that I dont know what kind of cast iron (Malleable, ductile, or what) it is and I didnt have a metallurgist look at it to see if maybe the chemistry is off such that it is weaker than was expected when they sized the casting. When I posted this I was wondering if others had problems - that would indicate a poorly designed, undersized component. No where in manual does it say not to leave pin in when the tractor is moving. My father in law and my father have Kubotas and love them. To say I am dissappointed is an understatement. Thanks again for all of the feedback, I really appreciate it.

Please follow up with us on this, and let us all know what the fix/response is from the dealer/kubota.

 

[PoTreeBoy]

Thanks for all of the input - I appreciate it. The dealer specifically told me to always have the pin in when driving tractor around for safety reasons. He indicated that the boom can swing left or right and represent a crushing hazard. I agree with some who posted that the fracture is a brittle fracture and there are no obvious inclusions or excessive pores in casting that would cause problem. Having said that I dont know what kind of cast iron (Malleable, ductile, or what) it is and I didnt have a metallurgist look at it to see if maybe the chemistry is off such that it is weaker than was expected when they sized the casting. When I posted this I was wondering if others had problems - that would indicate a poorly designed, undersized component. No where in manual does it say not to leave pin in when the tractor is moving. My father in law and my father have Kubotas and love them. To say I am dissappointed is an understatement. Thanks again for all of the feedback, I really appreciate it.

A previous owner of my BT900 welded short chains to each stabilizer and a grab hook to each side of the boom. The chains hold the boom up and keep it from swinging, replacing the (missing) pins, but it does put a side load on the stabilizers. My castings aren't broken, but I've wondered if they were in the past, or if this was done for convenience.