966D Refurbish and welding

alaskaforby4 · Mar 24, 2022

We picked up a 1985 Cat 966D at auction and have been going through it replacing all fluids and filters and doing a re-paint. Its quite the machine, much larger than the old C model. Cat did a full rebuild on it in 2012, it has 6700 hrs on it currently. Its been a solid machine so far, we've been extremely happy with it, dont make them like this any more.

After the re-paint a crack did appear tho....

alaskaforby4 · Mar 24, 2022

We did end up having to stud the tires, as these particular rubbers are extremely slick on ice, especially in the afternoon. One of our guys slid off a little driveway below, no harm done fortunately.

alaskaforby4 · Mar 24, 2022

Anyway after the first greasing of machine after paint job I noticed some old cracking shining through, on the main Lever 4E-3119 (4V8517) Cat wants $11,762 for said part. I did find a used one through Cat for 3100, shipped here. So they are available, which is nice to know. This isn't a production machine so I'm looking into the likely hood of having this welded up. I understand this is not a simple process being such a large chunk of steel and what appears to be cast steel potentially? So I thought i'd bring it here to the knowledge base as im sure someone has broken another one out there. Any luck repairing? Does cat have a procedure for such a thing?

I marked the cracks vertically with knife as you can see, to see if they were growing, and they dont seem to be...yet

alaskaforby4 · Mar 24, 2022

on the right side it appears to be stressing it somehow. Doesn't appear to be cracks, just stretch marks

Nige · Mar 24, 2022

Budget for a replacement tilt link. Those are cast and not repairable by welding with any success from everything I've seen.
To do any sort of a job the link would have to be removed from the machine, got into a heated shop then preheated to around 150 DegC before anyone thinks of striking an arc on it. I would imagine an electrode with very high elongation (so not 7018 then) would give the best chance of success. After welding it would need to be stress-relieved for something like 48 hours at 250 DegC if my memory serves me correctly. Is there a welding shop round your way with an oven big enough to fit it into after the repair.?
I have dozens of photos of tilt links broken in half that started as cracks like this. A lot of them originated from casting defects, the rest from operational abuse.
Bear in mind that a used replacement could be in a similar shape to the one you have on the machine right now.

Have you looked to see if there is anything obviously out of true in the loader linkage.?

Are you ever going to be loading dirt with it on a production basis.?

alaskaforby4 · Mar 24, 2022

Nige said:
Budget for a replacement tilt link. Those are cast and not repairable by welding with any success from everything I've seen.
To do any sort of a job the link would have to be removed from the machine, got into a heated shop then preheated to around 150 DegC before anyone thinks of striking an arc on it. I would imagine an electrode with very high elongation (so not 7018 then) would give the best chance of success. After welding it would need to be stress-relieved for something like 48 hours at 250 DegC if my memory serves me correctly. Is there a welding shop round your way with an oven big enough to fit it into after the repair.?
I have dozens of photos of tilt links broken in half that started as cracks like this. A lot of them originated from casting defects, the rest from operational abuse.
Bear in mind that a used replacement could be in a similar shape to the one you have on the machine right now.

Have you looked to see if there is anything obviously out of true in the loader linkage.?

Are you ever going to be loading dirt with it on a production basis.?

Everything seems to be plumb and strait, nothing bent. This won't be a production machine no, just loading some gravel here and there, snowplowing in the winter.

No there isn't an oven to fit it in unfortunately. There is a "new aftermarket" from Cat but I'm leary about that route as well

Nige · Mar 24, 2022

alaskaforby4 said:
There is a "new aftermarket" from Cat but I'm leary about that route as well

I think your are very wise to be leery of that option.

Nige · Mar 24, 2022

To give you an idea. This is a stress diagram of a typical tilt link. The lowest stresses are green, moving up through yellow to the highest stress areas in red. Your cracks are just on the boundary of the yellow/red area.

Nige · Mar 24, 2022

Here's a couple that failed with internal casting defects. In the frist one the little discolouration in the centre of the balck circle is the grain of foundry sand that started the internal crack. There was no sign of an external crack at all until the lever failed catastrophically.
The second one it's more obvious and there was indication of an external crack before it failed.

Nige · Mar 24, 2022

alaskaforby4 said:
This won't be a production machine no, just loading some gravel here and there, snowplowing in the winter.

TBH I think if I was in your position I'd just keep it under close observation, at least for now.
It is possible that those cracks were started by an operator banging the bucket linkage against the dump stops in an attempt to dislodge sticky material from the bucket.
Try and stay away from that type of operating practice and the tilt lever could give you long service without the cracks getting any bigger.

Another suggestion. Are the dump stops on the lever and on the cross-tube of the lft arms nice and flat.? Do the stops come together even or can you see daylight through certain parts when the stops are touching.? Do they look like the photos below.? I sure hope not.

alaskaforby4 · Mar 24, 2022

Nige said:
To give you an idea. This is a stress diagram of a typical tilt link. The lowest stresses are green, moving up through yellow to the highest stress areas in red. Your cracks are just on the boundary of the yellow/red area.

View attachment 255671

wow, thanks for that really cool diagram! Really puts it into perspective.
The failures are quite interesting also, heck of a way to start your day.

Do you think it would be worth trying to grind it out and metal glue it back up?
or the chance for actual success is so low I should just monitor it?

Its hard to say what previous operators were like, it does have a bent fork tip thats indicative of less than stellar operating techniques. But other than that everything seems in order. The bump stops are smooth and dont look beat up

Bluox · Mar 25, 2022

That Cat cast steel is usually quite weldable.
If you have a heated shop overnite and weld it on the machine.
Take a grinder with a flap wheel and clean the paint and rust off.
Use a regular grinding wheel to grind the crack out and leave a small V.
Use a torch to preheat warm enough to drive off the water.
You can weld with fresh 7018 and I weld stringer beads and slag with a needle scaler.
Don't get it too hot.
Grind the over weld off flush with the flap wheel and a lite coat of paint while warm.
If you have any questions PM me for a phone #.
Good luck
Bob

alaskaforby4 · Mar 29, 2022

Thanks for the reply and ideas, I think I'll budget for another one, then give it a go welding! I'll report back when it fails!

Jonas302 · Mar 29, 2022

Awesome job on the machine
And the educational photos from Nige are great too

alaskaforby4 · Dec 15, 2022

Well, made it through the summer! this crack may have grown a little bit, hard to say Or if the new paint just chipped more around it. I didnt attempt welding, sounded like mixed results locally, mostly failing.

alaskaforby4 · Dec 15, 2022

I did have another question about an injection pump leak on this machine. Maybe I should start another thread but ill try here first. Its leaking right out of the throttle linkage. There is a plate there id like to take off and re-seal. But wanted to ask beforehand to a bunch of springs dont come flying back at me.

We pressure washed it off real well to see where it was coming from, but it made a pretty good mess over the summer

Welder Dave · Dec 15, 2022

As far as the cracks they can be welded but if the proper technique isn't followed can make it worse. Preheat around 300F would be ideal because it's a thick piece of cast steel. I'd use something a little stronger than 7018 like 8018C3. This is the most common 8018 that doesn't always list the C3 in the name. The fine print will show it though. It has 1% nickle for added toughness and good for low temperatures. It's commonly used on crane booms. You could use one of the high strength stainless based specialty rods but that would be overkill. Wraping it in a welding blanket after welding so it can slow cool would be beneficial. Peening with a needle scaler while it's hot from welding would help relieve stress. If you don't have a needle scaler even a blunt/dull chipping hammer to peen the welds would help.
As far as the leak I don't know about a 966D but on my 931B track loader 2 seals could be installed on the throttle shaft cover if the 1st one was pushed in a little further.

alaskaforby4 · Dec 15, 2022

Thanks for the info Dave, we are somewhat sorta remote, there aren't alot of pro welder options.
I play around on the MIG quite a bit, but not fluent enough on stick to carry this out just yet.

For the pump, thanks for that info too, I really want to pull that cover off and see whats behind door #1 haha

Nige · Dec 15, 2022

If you want to have a bash at welding it I'd suggest a rod with more than 1% nickel. Eutectic Xuper NucleoTec 2222 was our weapon of choice in an attempt to avoid re-cracking and have an advantage of being low heat input too. If they work with the levels of expansion & contraction on nuclear reactors then that's good enough for me. https://www.castolin.com/product/eutectrode-xuper-nucleotec-2222-welding-electrodes
The price will make your eyes water though. Loads of pre-heat and post heat required plus beat the bejasus out of it with a needle gun after each pass to stress relieve the weld while it's still hot.
What worries me if you start chasing that crack is how deep it might actually go. The problem at the moment where that realization dawns on you is that you've already gone to the point of no return and have to keep going.

Here's a thought. Does anyone around your way have an ultra-sonic machine (similar to what's used to measure undercarriage wear) that could be run over the crack area in an attempt to determine how deep it is.?

Coaldust · Dec 16, 2022

Interesting Nige. I have not tried measuring cracks with my ultrasound gadget. I’ll have to read up on that.

966D Refurbish and welding

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