Recommendations repairing hydraulic cylinder trunnion

[jovol]

Hey, I have an L48 and the backhoe swing cylinders need some repairs. The trunnions on them are supposed to be 1-3/4" OD, they're closer to 1.65" now (not consistent either). Would it be possible for a machine shop to weld them back up and machine them back to spec? I'm not familiar with trying to fixture something like this, or the tool required to do the machining.

Thanks for any advice.
John

 

[North Idaho Wolfman]

Those are going to be tough to work with.
I think that's the best option
Keep in mind the case for that cylinder is available for about 1K.

 

[GreensvilleJay]

hmm, could the 'stubs' be made round, then bushings made ?

 

[fried1765]

Hey, I have an L48 and the backhoe swing cylinders need some repairs. The trunnions on them are supposed to be 1-3/4" OD, they're closer to 1.65" now (not consistent either). Would it be possible for a machine shop to weld them back up and machine them back to spec? I'm not familiar with trying to fixture something like this, or the tool required to do the machining.

Thanks for any advice.
John

Why not ask a machine shop if they can cut the pins flush, bore out to required size, and machine proper sized pin stock to weld (or cross pin) in?

 

[RCW]

Yeah, I can see how that'd be a challenge.

Not a single through-pin, but two anchored in a collar around the cylinder.

We've got some very good machinists here, but looks like re-building/machining to spec what's there might be best option?

This is a BT1100 backhoe option for L48. Looks like/similar to the photo.

 

[jovol]

Is there a tool for a mill that can machine the OD of the pins? Kind of like a plug cutter. If there is, I imagine welding it up and using that tool would be the way to go. I'm not sure what that tool would be called. If I knew it might make it easier asking machine shops if they have that tool. Or maybe a CNC with a normal endmill can be precise enough. It doesn't seem feasible to chuck the barrel in a lathe using the opposite side pin, 1 because the trunnion is not centered on the barrel so the weight imbalance would be substantial, and 2 the pins aren't true. I'm not sure, maybe a pro machinist would have a different opinion.

@RCW that is the correct parts diagram.

Those are going to be tough to work with.
I think that's the best option
Keep in mind the case for that cylinder is available for about 1K.

By the case, do you mean the trunnion mount that get's welded to the barrel?

 

[mcfarmall]

Use a single point boring head in a mill. Do one side, flip it over and do the other. Spin out a couple of bushings and weld them on the pins.

 

[Jsjac]

I would say buff it with a Scotch bright pad and install new bushings and call it good.

 

[jovol]

Use a single point boring head in a mill. Do one side, flip it over and do the other. Spin out a couple of bushings and weld them on the pins.

Thank you. That turned up this YouTube b vid, which helped me see how it works

 

[North Idaho Wolfman]

By the case, do you mean the trunnion mount that get's welded to the barrel?

This is the Case / Tube assembly

 

[North Idaho Wolfman]

Have you pulled the bushings to make sure you haven't worn them down past being replaceable?
If they are replaceable then your good to go after you resize the cylinder back to size.
If they are not replaceable because it's worn through them, then your looking a lot more work!
Line boring the frame is a huge deal.

 

[TheOldHokie]

Is there a tool for a mill that can machine the OD of the pins? Kind of like a plug cutter. If there is, I imagine welding it up and using that tool would be the way to go. I'm not sure what that tool would be called. If I knew it might make it easier asking machine shops if they have that tool. Or maybe a CNC with a normal endmill can be precise enough. It doesn't seem feasible to chuck the barrel in a lathe using the opposite side pin, 1 because the trunnion is not centered on the barrel so the weight imbalance would be substantial, and 2 the pins aren't true. I'm not sure, maybe a pro machinist would have a different opinion.

@RCW that is the correct parts diagram.

By the case, do you mean the trunnion mount that get's welded to the barrel?

Its just a cylinder trunnion - nothing high precision in terms of the alignment. Restoring the diameter of the pins is the central goal. Weld thwm up and regrind. A decent (i.e. creative) machine shop will figure out a way to swing it for grinding. I can think of a couple possibilities with what I have in my little shop. Probably going to be a bit pricey but not break the bank expensive.

Same for the bores in the frame. Bore oversize and bush back to size.

Dan

 

[Lil Foot]

Use a single point boring head in a mill. Do one side, flip it over and do the other. Spin out a couple of bushings and weld them on the pins.

I used this method to re-machine the swing pivots on my backhoe.
After cleaning up the damage, it was easy to make oversize bushings for the mating parts.
Here is a thread in which myself and another gentleman shared info on rebuilding our B670 Backhoes.
We both had worn out swing pivots (trunnions) and tackled the problem in different ways.
The pertinent pics are in post #2, #4, #7, #12, #16, #17.

B670 Backhoe Rebuild

Does anyone have a working knowledge of the older B670 (KUW200) backhoes that were made for the older B6100 Kubota tractors. I am trying to rebuild one and have found that the area that the bottom pin of the swing weldment goes into is worn out and out of round. The raised round piece of metal...

www.orangetractortalks.com

 

[jovol]

Fortunately the boss for the bushings are still good. I’d rather stick to spec sizes so kubota’s greaseable bushings do the job, although I’m sure there are off the shelf ones close in size. The spec bushings are 1-3/4 id, 2-1/8 od, 1-1/4 long.

@Lil Foot thanks I’ll check that out

 

[Dustyx2]

Turning an od in a mill is called trepanning. They can be welded and trepanned in a horizontal boring mill. I've done several over the years, but nothing on one that small. The ones I have done were on mining equipment.

 

[mikester]

I'd price out a new one and delivery timing then get an estimate from your local machine shop to fix yours and how long they'd take to fix it.

If your machine is a money maker then your decision is made for you.

 

[jovol]

Just wanted to round the thread off. A local machinist turned the trunnions on a mill with an outside boring head (exactly like this video on youtube

) and slipped a hardened sleeve over the trunnions with a 2-3 mil interference fit. He did both cylinders for $350, a good bit of savings over replacing both barrels.

 

[North Idaho Wolfman]

I've watched a ton of his videos.
Just have to downsize for what little things I work on, but really good info!