Kubota Hydraulic cylinder with broken piston rod

[ejnichol]

I did a nice job in breaking my BX24 back hoe. On the dipper cylinder looks like I broke the piston rod where the piston bolts to the rod. Don't have it apart yet, waiting on spanner wrench to arrive. Based on how it went down and it floppiness now I believe the threaded part between nut and rod at the piston broke off inside cylinder.

Thought I'd asked if there are any other sources for replacement rams or the rod itself other than Kubota. Pricey stuff.

 

[Tinhack]

What kind of shop equipment do you have? You can buy everything to build a cylinder, but you'll need machines to customize the parts. You may be better off taking the cylinder to a hydraulic shop and let them repair it. Most will have the tools and equipment to rebuild cylinders.

If you blew the piston off the end of the rod as you suspect, even just a new chrome rod is not going to be cheap. It will need to threaded, cut to length and a new end welded on. It sounds like you're expecting too much from your BX24.

 

[Roadworthy]

If you have a local hydraulic shop they can tell you whether it's practical to repair the cylinder or just replace the whole thing. I'm sure they're less expensive than Kubota.

 

[LD1]

Local shop is your friend.

But maybe you will get lucky and it just came unthreaded?

Get it apart and post some pics

 

[ejnichol]

I'll post up some pictures when I get it apart. Should be interesting. The piston still moves when commanded but it not attached to ram that much I can tell.

If I could find a tlb more robust/faster cycle rate but not much bigger I'd trade up. It a good machine for it size and served me well since new in 2007.

I messed up but first break down so I can't complain.

 

[ejnichol]

Updating.

As you can see it pulled the nut off. Machine shop options in this area where machine is are limited.

Ended up at what turned out to be a non qualified machine shop. They screwed it up by trying turn it down and threading with a die.

They went through two dies and ended up with a failed 14mm thread. There only suggestion was to weld nut on.

If I take it do a 'qualified' shop I'd end up with something around 12-13mm dia.. This would be too small when it was originally a 17-18 mm threaded shaft best I can tell.

So my options are new rod and nut. Delivered best price I could find $ 400.00. Other option would be to weld 14mm nut on.

 

[ptsg]

Updating.

As you can see it pulled the nut off. Machine shop options in this area where machine is are limited.

Ended up at what turned out to be a non qualified machine shop. They screwed it up by trying turn it down and threading with a die.

They went through two dies and ended up with a failed 14mm thread. There only suggestion was to weld nut on.

If I take it do a 'qualified' shop I'd end up with something around 12-13mm dia.. This would be too small when it was originally a 17-18 mm threaded shaft best I can tell.

So my options are new rod and nut. Delivered best price I could find $ 400.00. Other option would be to weld 14mm nut on.





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I know you said it's hard to find a good shop, but try find another shop that could go away with the threaded section (leaving just enough diameter to center the piston) and drill and tap for a good quality bolt.

That would be a $20 to $30 job on my shop.

 

[ejnichol]

I know you said it's hard to find a good shop, but try find another shop that could go away with the threaded section (leaving just enough diameter to center the piston) and drill and tap for a good quality bolt.

That would be a $20 to $30 job on my shop.

That's an idea tapping the end for a bolt. Not sure how the bore would be threaded as I understand the steel rod is induction hardened and not easy to thread. This hardness is why shop went through two dies with no success but shallow mangled thread.

My limited knowledge leads me to believe that it is worked on a lathe with special hardened cutting tools to get threaded.

I took it to a automotive machine shop I used to machine heads before and he correctly declined as he doesn't have a lathe to do. Wish other shop had that much common sense.

Your shop is very reasonable if you could thread that steel for that price. The shop that butchered this wanted 110.00 shop time which I refused to pay.

Thanks

 

[ptsg]

That's an idea tapping the end for a bolt. Not sure how the bore would be threaded as I understand the steel rod is induction hardened and not easy to thread. This hardness is why shop went through two dies with no success but shallow mangled thread.

My limited knowledge leads me to believe that it is worked on a lathe with special hardened cutting tools to get threaded.

I took it to a automotive machine shop I used to machine heads before and he correctly declined as he doesn't have a lathe to do. Wish other shop had that much common sense.

Your shop is very reasonable if you could thread that steel for that price. The shop that butchered this wanted 110.00 shop time which I refused to pay.

Thanks

Only an outside thin layer is hardened, less than 1 mm thick usually. The center of the rod is actually very soft and easy to machine. The threaded portion shouldn't be hardened at all.

Pretty sure the shop didn't even setup that rod on a lathe. They went the cheap way and tried holding the rod on a vise then tried to run a die on it. Couldn't align it up properly and made and an entire mess out of it.

Looking closer at the pictures, if that's an M18x2 thread, looks like it could maybe be salvageable by going to M16x2, since they didn't really turn the diameter down so there is still "meat" to work with.

Worst case scenario, just shove a M18x2 bolt through like I said on the other post.

Just for reference, I machined the cylinders on my loader myself. All 4 of them, rod, piston, barrel, ends, etc. Just for the rod, I paid around $90 and around $85 for the barrel material. I could machine a brand new rod for your machine for around $120 easily and still made a good profit.

 

[LD1]

Yea, lathe with hardened inserts to cut them threads.

Possibly but I would doubt the threads were induction hardened.....or at least it was probably threaded before it was hardened.

I wish you had a good hydraulic machine shop around you.

I had to replace the rod on my one of the cylinders on my 334 bobcat excavator. It was 1-3/8" diameter rod and about 30" long. They cut off the old rod end, welded to a new shaft, turned the threads for the piston, etc. Basically a bran new rod and about twice the size of yours and it was $350

But sadly I think you are down to a new rod (or having one made). The original threads pulled.....anything smaller is just gonna be weaker, including drilling and taping for a bolt that will be a smaller diameter as well

 

[ejnichol]

They did something to turn it down attempted threading and then shoved a 14mm nut on it. They knew it wasn't r/r serviceable and so they could only offer welding nut on.

That picture is of it as it came out of cylinder.

 

[ptsg]

They turned it down attempted threading and then shoved a 14mm nut on it. They wasn't r/r serviceable and so they could only offer welding nut on. That picture is of it as it came out of cylinder.

Ops. My bad. Forgot the picture was before the machine shop ordeal.

 

[Mike1955]

I know you said it's hard to find a good shop, but try find another shop that could go away with the threaded section (leaving just enough diameter to center the piston) and drill and tap for a good quality bolt.

That would be a $20 to $30 job on my shop.

Id be willing to drive 100 miles for a good independent shop. Kubota is just to expensive. It isn’t that complicated but experience is worth a lot. Just my two Pennie’s worth!

 

[ejnichol]

Just for reference, I machined the cylinders on my loader myself. All 4 of them, rod, piston, barrel, ends, etc. Just for the rod, I paid around $90 and around $85 for the barrel material. I could machine a brand new rod for your machine for around $120 easily and still made a good profit.

The challenge is finding a competent shop that could get me back to work for 150.00 or less. Then there's the total time commitment. I 've spent 6-7 hours in time just talking and traveling with two shops just to figure out that who the qualified shop might be.

Time factor of getting it back to work and minimizing cost.

I ended up welding 14 mm nut on it. Welding or center tapping existing rod and bolting were only ways to deliver strength need from remaining mass. Finding a shop to center tap, what it would cost and time to do all this and get it back to work moved me to weld.

After 6-7 hrs of digging with back hoe its holding up fine. If it were to break off again then I'd order new parts. I needed to get on with the work at hand.

Thanks for taking time to comment as this has been an interesting learning experience.

 

[ptsg]

The challenge is finding a competent shop that could get me back to work for 150.00 or less. Then there's the total time commitment. I 've spent 6-7 hours in time just talking and traveling with two shops just to figure out that who the qualified shop might be.

Time factor of getting it back to work and minimizing cost.

I ended up welding 14 mm nut on it. Welding or center tapping existing rod and bolting were only ways to deliver strength need from remaining mass. Finding a shop to center tap, what it would cost and time to do all this and get it back to work moved me to weld.

After 6-7 hrs of digging with back hoe its holding up fine. If it were to break off again then I'd order new parts. I needed to get on with the work at hand.

Thanks for taking time to comment as this has been an interesting learning experience.

I totally understand. Not everyone is right up close to a good shop, which can make it an interesting experience indeed.

At least you got it going again so you can keep doing your stuff. Plus you gathered some ideas for the future.

 

[ejnichol]

Id be willing to drive 100 miles for a good independent shop. Kubota is just to expensive. It isn’t that complicated but experience is worth a lot. Just my two Pennie’s worth!

Yea there prices are too much. I would have liked to just order new rod and nut but just cant justify at this time.

 

[pmsmechanic]

Obviously the nut isn't going to turn off again. I think you've made a perfectly acceptable repair under the circumstances. And if you need to disassemble the rod for repairs I would take it to a lathe and machine the weld off and re-weld once repaired. $400 is $400!

 

[WranglerX]

Seems to me a really good hydraulic shop or "machine shop" could do a weld buildup in threaded area and then chuck it up in a lathe and turn it down to factory specs (diameter) and then cut new threads .... End process should look like it never ever had a problem.... But then it's all about the shop you find and the quality of work they do at a cost you find acceptable.......

 

[4570Man]

If you haven’t already screwed up the cylinder barrel and contaminated the system with metal shards you dodged a bullet. I’d do a careful inspection to make sure that’s not happened and buy a new rod and go on.

 

[4570Man]

Seems to me a really good hydraulic shop or "machine shop" could do a weld buildup in threaded area and then chuck it up in a lathe and turn it down to factory specs (diameter) and then cut new threads .... End process should look like it never ever had a problem.... But then it's all about the shop you find and the quality of work they do at a cost you find acceptable.......

I don’t think a good shop would do that repair. The rod already broke once under the optimal conditions. A weld will compromise the heat treat and make the rod weaker than it started.