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.





View attachment 825382View attachment 825383View attachment 825384

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