Calling Case 621 (c I think) gurus...

[Tony Wells]

OK, I know this isn't the right way to approach this, but here goes....

I have no year of mfg, no serial number. What I was handed, as the house machinist, is a pin, location unsure. Somewhere in the rear frame/suspension zone. It is broken. I can tell you a few things about it, and maybe someone can steer me to at least the correct name.

It's a bit over 2-1/4" OD, undercut (relieved) in the center. Approximately 16" long. The ends (~4") have had additional heat treating, such as case hardening such as nitriding, carburizing, or flame or induction hardening. File hard. It's probably Metric, so these are just rough measurements on broken pieces. Each end face has two drilled and tapped holes, 180° apart. There are flanged caps that are bushed to receive the hardened and ground ends of this "dogbone". Each cap fits closely in a bore I suspect in a frame member, since there are also two jack-screw holes tapped in the flange. It would seem that with everything aligned, the two bolts on the end faces pull the caps into position where they are in turn bolted to the frame. or vise-versa. I suspect there may be shims involved to set end play but I can't be sure.

This seems like a part that would have common usage among machines with similar frames, but I can't be sure. All I got was the pieces, and new caps to fit to. I'll have to establish an accurate OAL, especially if my supposition about shims is wrong.

By that description, can anyone at least tell me what the proper name of this pin is? Given time I can come up with the machine data, but for the moment, it's lost. I've been told the OEM is about $850, but long lead time. I think that was a guess.

Meanwhile, the machine is obviously down, and while we need 4 wheeled loaders, only 2 are running....both with no heat, so have whining operators. After all, it's only in the teens.....well has been a couple of days. My thing there, other than sympathy for the ops, is fogged glass and loss of visibility. Someone or something is going to get run over. Heater cores seem to be clogged on the Doosans. Glad those aren't on my list.

Thanks for any help!

 

[Vetech63]

Sounds like the cradle pivot pin

 

[Tony Wells]

This is a New Holland diagram, but same layout I suspect. I think you are right. I have only item #8 (2x) as new parts. The pin I'm to make is item #4. I'll need to hustle up the shims (#7) and seals, bolts, etc. But that's what it looks to be.

So next, from an engineering standpoint, I understand the hardness requirement, but I'm unclear on the transverse load. How much weight is on this pin, and is it a shock load? I assume it must be substantial, being the back end of the machine, with the counterweight and engine, but how much "bounce" does it see? I've got to select the material (4340 probably) and heat treating.
I'm hoping the minor parts are available. Otherwise, I'll just have the customer wait. Or if I don't want the risk and liability, I'll pass. But this is what I've done all my working career. Reverse engineering is always a challenge....and fun!

 

[Shimmy1]

Whatever you would make a bucket pin for an excavator out of?

 

[Tony Wells]

Usually I make them from 4140HT, which is a tool steel technically, using a broad definition of "tool". Commercial heat treat comes in around 34Rc, with a tough core. It's a good all around steel for that, unless you have to have chrome for some reason. It's also softer than bearing race style bushings, making the pin the sacrificial part. It wears out before the bushing, and can be replaced without messing with weld up and line bore if you keep an eye on it. 4340 is a little stronger IIRC, so if I have some on hand that's what I'll use. If there is a question of surface hardness on the ends, I can case harden it, but typically shop processes are only a few thousandths thick. Nitride, carburize, etc. can get much deeper. Induction hardening is likely what the original part has had done. I'm not sure it will be practical to follow the same procedures, but I know a few heat treaters I can lean on for recommendations. I just know I need to control the gradient change back to the standard hardness to avoid stress points.

 

[8V71]

AKA:Case calls it a rear axle trunnion Cat calls it rear axle oscillation
621C parts picture this does not look like the pin you described. Maybe a different model

 

[Shimmy1]

AKA:Case calls it a rear axle trunnion Cat calls it rear axle oscillation
621C parts picture this does not look like the pin you described. Maybe a different model

That looks identical to our 621B.

 

[Tony Wells]

I looked at that drawing, and it's definitely different. That approach uses two shorter pins with integral flanges to tie to the frame. I'll have to get the specifics of the machine. The info I got was from the shop manager, and since I'm about 90% deaf, I probably misunderstood at least part of what he said. I can only confirm with some degree of confidence that the pivot pin "caps" as I am calling them for now are pn 87731988.

In my case, the "caps" and pins are separate and only a single, longer pin.

 

[Tony Wells]

OK, more info. It's actually a 621 E. VIN N7F202824

 

[Tony Wells]

Current pin condition. Snapped like a twig. Looks to me like it's hard all the way through. If that's the case, the mfg strategy I'll have to change. If I make it softer, it will bend, and the "caps", which I believe are properly called pivots, will crack. Both the old ones did. I'm just having a hard time understanding how this broke. I would guess that it would be engineered to withstand as severe a blow as the machine could dish out, with the rear wheels off the ground and the bucket falling off and letting it slam the ground.

 

[Shimmy1]

Most operators of that size loader today can destroy an anvil with a rubber mallet in an hour. If you had to watch some of these guys for a day, you'd quit your job, because you'd have no interest in fixing their messes anymore.

 

[John C.]

Most of the bad wheel loader designers seem to end up at the lesser quality manufacturers.

The first issue I'm seeing is the damage on the ends of the pin possibly indicating a problem with putting grease in a couple of fittings. Hough called all that monkey motion on the back axle a bolster. What I've experienced on failures of that is the lack grease and backing the machine into things over time. The frame mounting points get sloppy and the problem compounds as time moves forward. All the beach marks is what I'm basing those comments on. I also see what looks like a radial crack indicated by the black mark on one end of the pin. I could be wrong about that. I would be surprised if that was a bolster pin because of the smaller diameter in the middle of the pin. How would you get bearings to fit over the larger diameter of the pin and then seat on the smaller diameter? I'm also wondering about what was broken off the ends of the pins? I would think from the bolt holes that there would be retainer caps on the ends.

Loading on the back axle is nothing compared to the front and I would guess it would only involve the weight of the back half of the machine and any shock loading when backing into something or slamming down when the back was picked off the ground. I don't recall if a Case 621 could even pick up the back of the machine by loading the bucket.

I think that you might consider laying off this job until you have all the facts about what it is.

 

[Tony Wells]

John, there are what they call "pivots" that bolt to the pin with the two holes, or what's left of them. There is about 2 1/2" snapped off each end that forms a metal on metal bearing point in a cup in the pivot caps. The pivot caps have a flange that positions the pin in the axle housing. See post #3. All the stress is concentrated on the very ends where that pin fits into the pivot cap and in the axle housing, two adjacent diameters on each end. I haven't looked at the housing itself to see if the bushings have survived. Seems unlikely they will be usable.
The upset area again is a metal on metal bearing point in the axle housing. The reduced area in the center is non-contact. Just makes sliding it through the axle housing easier. Those pivot caps are item #8 on that diagram. The diameter is reduced slightly where they fit into the caps. Not shown is the frame that those caps fit through. The pivot caps have flats machined on them to prevent rotation, it appears. It's purpose is to allow the axle to tilt on that pin to let the wheels float or the machine tilt on the axle, however you want to look at it.

I'm not committed yet....just getting the information I need to say yay or nay. A new pin runs about $750, I'm told. With the special heat treating and probably grinding to finish size, I can see why, and may not be worth my time making it. I have all the stuff to do it, but it's a time vs money thing, as usual.

 

[Tony Wells]

Shimmy....I know what you mean. I can't explain how they do it.....but they certainly do.

 

[Vetech63]

Seems to me the machining and hardening time and expense would be more than $750.............and that's not including the cost of downtime during the repair. If it was obsolete, then I can see going through those motions.

 

[Tony Wells]

Vetech, you're right about that. It's been down as a spare for several months. It's just that the Doosans are going down, so trying to hustle up some other loaders. That part is available, just not quickly. But then, I have plenty of broke down equipment to work on. It's just that I have the machine shop, so it was proposed that I recreate it rather than buy. The more I think about it, the less I want to machine it though.

 

[alrman]

The CNH part number for the pin is 87695939 which subs from 87450043.
The new part number may possibly indicate an upgrade, but that isn't always the case.

This website says they have one in stock - but never believe anything on the internet.