Kubota backhoe cylinder fitting welds are horrific

[Lefty7]

My BH92 backhoe is 5 years old. Since new the welds at all the cylinder fittings have been deteriorating rapidly. First the paint disintegrated. Now chunks of corrosion are falling off.
Visited a buddy today who has owned a Wood backhoe since 1992. The same cylinder welds on his tractor are pristine including the original paint. What the???Clearly I’ll need to replace the welds at my expense which is a bit ridiculous in my opinion.
Can anyone chime in on how this came to be? Surely the welders and metallurgists at Kubota know what they’re doing so then I ask how could they be so far off the mark? And most importantly how can I make certain this never happens again??

I have the same backhoe on my L3940HSTC, ordered new with the tractor in 2012. All of my cylinder welds are perfect as is the paint covering them - although I will mention that unless it is mid-job or onsite, it is kept in a roofed shed. ~Lefty7

 

[crazyal]

If it was mine I would put some labor into it and stop the problem. First remove the lines and put plugs in the cylinders so you can remove them. Then I would sand blast the rusted parts to strip any flaking metal and rust. If you have a local bridge painting company they use some of the best primers you will ever see for steel. Because of the salt and rain bridges see they use primers with far more zinc than normal primers. I've used a primer from a company called Wasser that was something like over 80% zinc when dry. Then get the correct color paint from Kubota. Chances are you'll never have an issue with it again.

The other option would be to replace the cylinder when they start to leak, and they will at the worst time, or try to have a welder replace the bungs. Chances are what's going to happen is the bung will get too thin and break when the cylinder is under load. For a loader that would mean with a bucket full of dirt that comes crashing down spraying hot oil everywhere.

 

[Ackman]

I have the same backhoe on my L3940HSTC, ordered new with the tractor in 2012. All of my cylinder welds are perfect as is the paint covering them - although I will mention that unless it is mid-job or onsite, it is kept in a roofed shed. ~Lefty7

Thx for the input. Some other replies have noted the backhoe cylinders are outsourced. I don't know the details so I can't comment but I do know these bungs started to deteriorate from day one. I noticed it after first use in 2018 (4 years old, not five!) with a brand new L4060- paint fell apart within a month but what surprised me was the amount of steel attached that was not just surface rust. The first picture above more accurately describes the other 12 connections; the second picture is probably the best condition of my 14. Yikes. Would it be possible for you to take a picture of a weld/ fitting from your backhoe for me? The reason for asking is I'd like to see if the backhoe you have is different from mine in this regard.
A buddy has a smaller backhoe; a Woods from 1990-1992 +/- on a 27 hp Kubota b series. He has plenty of surface rust on a tractor that has never seen the inside of a garage. He's at a point now of replacing hoses, fel cylinders and leaking seals. I'll try to post an image that shows what 30 years of salt air will do. Interesting.... Thx again

 

[Ackman]

If it was mine I would put some labor into it and stop the problem. First remove the lines and put plugs in the cylinders so you can remove them. Then I would sand blast the rusted parts to strip any flaking metal and rust. If you have a local bridge painting company they use some of the best primers you will ever see for steel. Because of the salt and rain bridges see they use primers with far more zinc than normal primers. I've used a primer from a company called Wasser that was something like over 80% zinc when dry. Then get the correct color paint from Kubota. Chances are you'll never have an issue with it again.

The other option would be to replace the cylinder when they start to leak, and they will at the worst time, or try to have a welder replace the bungs. Chances are what's going to happen is the bung will get too thin and break when the cylinder is under load. For a loader that would mean with a bucket full of dirt that comes crashing down spraying hot oil everywhere.

Thx for the advice. I ordered Ospho, expecting it to arrive soon. I'll use a metal brush attachment to clean them as well as I can and apply the treatment, prime and paint. I'm not optimistic I can remove the 90's from the bungs. Unfortunately the excellent welder I use is out of country right now but I am definitely planning a visit to his shop when he returns. I was told to expect $100 per weld / fitting replacement; at this point $1400 is short money to get it done right and go forward. I'm hopeful the cylinder seals are in good enough shape to reuse.

 

[Ackman]

Apparently the galvanic reaction of mild steel (weld) to ss fitting is the culprit. Time for new…..

Thx for chiming in- appreciated. One thought I had is regarding what kind of grounding the tractor uses. As in with each use of the bucket is it possible or likely that the tractor is sending some kind of electrical current through the backhoe and accelerating this galvanic reaction? Any thoughts? Thx again, Eric

 

[TMGT]

Thx for chiming in- appreciated. One thought I had is regarding what kind of grounding the tractor uses. As in with each use of the bucket is it possible or likely that the tractor is sending some kind of electrical current through the backhoe and accelerating this galvanic reaction? Any thoughts? Thx again, Eric

The fittings aren't stainless steel, they are zinc plated. My guess is the supplier of the bugs had a problem as even the weld doesn't show any signs of degradation.

Sometime the bungs are cast steel, sometimes they are machined from bar stock.

If they are cast, I've seen issues with a bad batch of castings rust and deteriorate quicker then the material around it in other applications.

If you do need to remove the fitting from the cylinder I doubt you'd have any issue, you'd be surprised how easy the fittings come out, even with the bung looking that bad.

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