Bearing and pin metallurgy (Komatsu excavator)

[seattle smitty]

I do miscellaneous repairs, mostly welding, for a small landscaping contractor with a selection of heavy equipment. In this case, his Komatsu excavator with extend-a-hoe (I think it's called) shows a lot of slop in the pivot joints at the end of the crowd arm where the bucket attaches. Yesterday I pulled the two lowermost pins; they didn't show a lot of wear, but the bearings are quite worn, with lots of clearance to the pins. I phoned the dealer and was stunned by the prices of new bearing sets and seals. To replace all of these at the bottom of the stick will be well over a grand!. Since the housing crash, my contractor friend has barely been braking even, and doesn't have a thousand dollars to use merely to tighten up his buckets. So I'm figuring I can make some bearings on a lathe, at least for short-term use.

I was impressed that Komatsu used good, wide bearings with lots of surface area, so that they didn't pound out, they just wore out from the grit that eventually gets past the grease and the seals. I have removed such bearings from other machines by running a few weld-beads across the I.D. to shrink them, which I think is standard practice.

I'd be interested if any of you is familiar with the metallurgy usual to these pins and bearings. I have made new pins using through-hardened 4130 since it was easy to find, and I didn't have any information to go on. This material is easy enough to drill and saw. In the current project, however, I don't need to make pins.

It would probably be easy enough to find some thickwall mild steel tube (in inch dimensions) out of which I can turn the metric-sized bearings. Will mild steel work, or will it pound out in a hurry? As I say, these bearings are nice and wide.

What are the alloys customarily used for pins, and for bearings?

Appreciate any help,

--Smitty

 

[RayF]

Most bearings are made out of EN14A which is pretty well mild steel and then carburised in a furnace to harden it. Thats beyond the average workshop.
I have made bearings successfully which have lasted well out of 4140. Machine the O/D oversize. Heat to cherry red and quench in oil.Final machine with ceramic tips.
With pins the best is machine them out of 4140 or better and induction harden. You can buy chromed induction hardened cylinder rod which may be OK. I'm not sure about the depth of hardness.

 

[leisureexpress]

An option to take up the area of the bore is to machine a piece of mild steel to the same OD as the bearing, then make the ID of the mild the same size as a common hardened bushing that has the hard ID for the pin to wear on. It might be kind of a hack fix, but it would probably be easier/cheaper than trying to accurately heat treat the steel if you're not set up for it.

I have a question on using the hardened cylinder rod - how do you drill the stuff for a retaining pin/bolt? I know for making a circlip land one can chuck it up in a lathe and use a toolpost grinder setup.....

 

[John C.]

There is an outfit down in Kent that can heat treat or harden anything you bring in to them.

There is a reason those things are so expensive. The bushings and the pins are perfectly matched to run together. You can go buy a standard bearing and have it machine ground to fit your application and it will be gone in weeks. Buy the factory bearing and it will last for years with decent maintenance. The life cycle cost of the factory bearings more than pay for themselves over the do and redo of custom made.

Good Luck!

 

[seattle smitty]

Thanks for the help!

Leisure, if you're asking about the 4130 I used for pins, it is heat-treated to through-harden, but not case-harden, so it drills okay. I can get it off the rack at Metal Shorts, a local outfit John will know.

John, I don't doubt that the factory bearings are the best for the job, even having the fancy weaving grease-slots that you see illustrated in machine shop texts, but which I have never yet tried to do myself. But the owner of the machinery wants to see if we can do a cheap fix that will hold up for a while. And while a properly-clearanced and case hardened bearing will resist the wear from grit better than other options, I have seen (in my limited experience) some "wrong" bearings hold up reasonably well . . . in the care of the same fellow, who is good about greasing his machines but then really hammers the bejesus out of them in the field. I did a massive rebuild of a PSM rockhead years ago, and replace the pivot pins and bearings of the jaws. Some of the fix was rough, in-the-field, not-very-close-tolerance work, including re-boring the mangled bores that held the pivot bearings. I bought four off-the-shelf bronze bearings, they being that only choice that was quick to do. I was able to incorporate some end-seals. These bronze bearings were long, with lots of surface area, and the difference between O.D. and I.D. was about a half inch, thus 1/4" wall, pretty thick. I told the owner to make sure to keep them greased, and though this rockhead hasn't got a great amount of use over the years, still the bearings have held up rather well, last I looked. So, without arguing with you, John, it seems that sometimes a guy can successfully get away with less-than-best options.

 

[John C.]

Smitty,
Love the response. I have gotten that a lot over the years. Getting away with something is the key phrase from all that don't have enough money.

If you want to "get away with it" for awhile then use bushings made of aluminum bronze. It will hold the grease and not beat out real quick and if it does get run without grease, it won't grab hold of the pin and gall it all up. That material is still expensive but not as bad as the exotic from Asia.

When people run the "get away with it" phrase on me, I usually require half payment up front and the rest before I install any parts.

Good Luck!

 

[tctractors]

In the U.K. we have a few outlets for non O.E. pins and bushings, Digbits being one, their parts are about 40% of the cost if not less than O.E. parts, the top hat bushings fitted to the bucket pin location is a common thing for myself to tackle, but I always press the new bushings home as they need to be firm in this location, it is important to fit the correct seals and O rings to help keep the dirt out and grease in.

 

[Komatsu 150]

Off topic a bit but I've had several customers over the years who insisted I do something in a particular way (usually cheap and nasty) and then come back later, even years later, and complain. When someone says "I'll take responsibility" anymore I just run away.

Smitty,
Love the response. I have gotten that a lot over the years. Getting away with something is the key phrase from all that don't have enough money.

If you want to "get away with it" for awhile then use bushings made of aluminum bronze. It will hold the grease and not beat out real quick and if it does get run without grease, it won't grab hold of the pin and gall it all up. That material is still expensive but not as bad as the exotic from Asia.

When people run the "get away with it" phrase on me, I usually require half payment up front and the rest before I install any parts.

Good Luck!

 

[seattle smitty]

Agreed . . . but . . . with some old customers you can develop a level of mutual trust and understanding, and you can say, "Remember that was just an experiment, a temporary fix to hold you 'til we could do it right?", and they'll say, "Oh yeah, I guess it was at that". Of course, then you and they will marvel at some temporary fixes you did that held up amazingly well, . . . and hope you haven't done an expensive "correct" fix that did NOT hold up!!

If I don't do cheap fixes these days, I'll have very little to do. I haven't looked around this website in a long time, but I'm sure that if I look i could find some comment along the following lines. The housing market and banking crashes and consequent recession have meant that a lot of smaller operators of heavy equipment are barely hanging on, barely able to cover their overhead. I can hardly call them cheapskates for wanting patch-jobs just good enough to get them through the recession.

 

[Scrub Puller]

Yair...I used to build and modify bits and pieces of gear by utilizing aftermarket track bushes for bearings. you need to build up and bore out the flogged out housing and choose a trackbush size to fit... D6, D8, D9 whatever. They cut okay with a chopsaw and it works out pretty cheap...if you want to grease them though you'll need to also make the pins.

Cheers.

 

[Komatsu 150]

Of course no criticism meant. With customers you trust it's a totally different story. Some people will stand up for what they say and some people have "selective memories". We're doing whatever we have to just to stay in business. I'm not doing anywhere near the types of maintenance on our equipment that I should.

Agreed . . . but . . . with some old customers you can develop a level of mutual trust and understanding, and you can say, "Remember that was just an experiment, a temporary fix to hold you 'til we could do it right?", and they'll say, "Oh yeah, I guess it was at that". Of course, then you and they will marvel at some temporary fixes you did that held up amazingly well, . . . and hope you haven't done an expensive "correct" fix that did NOT hold up!!

If I don't do cheap fixes these days, I'll have very little to do. I haven't looked around this website in a long time, but I'm sure that if I look i could find some comment along the following lines. The housing market and banking crashes and consequent recession have meant that a lot of smaller operators of heavy equipment are barely hanging on, barely able to cover their overhead. I can hardly call them cheapskates for wanting patch-jobs just good enough to get them through the recession.

 

[John C.]

I'm not finding fault in what anyone is saying. My comments are a reminder that the only business I worry about is my own. That means I'm real careful anymore when someone wants to throw a cheap fix into something that they are basing their business on. The thought pattern is that if they can't repair their iron, how are they going to pay me?

I have had several long term customers disappear in a puff of smoke with debt laying all around. Many drove high dollar fancy pickups dragging trailers around carrying every type of toy for any season. Yet with all that they couldn't afford a bushing to tighten up a bucket so they could run pipe grade. Cutting corners is OK and preferable where warranted. All I'm saying is keep your eyes open and make sure of your paycheck.

 

[seattle smitty]

Oh, I'm with you, John. There are some jerks. OTOH, some of the guys with fancy pickups and toys got them during the boom, and really are in tough shape today . . . and of course none of us can get anything much for the stuff we bought during the good times.

A chronic problem in doing jobs for small contractors is that you can't get work from them (or as you say, get paid by them) until they get paid by THEIR customers. And their customers are themselves waiting to get paid by someone. There can be quite a chain of people waiting to get paid before they can make their own payments. This is the standard scenario even in good times, but it is hugely exaggerated right now. And it appears to me that the worst offenders are the big outfits: they play the bank-interest game, hanging on to the little guy's money as long as they want because they have him over a barrel. They know he won't complain, or sue, because he needs more work and can't get the reputation of being uncooperative.

 

[John C.]

You really drove the spike into the timber on that. I've had a few customers jump off that train recently and move their operations to North Dakota. They would rather take the risk in a place where there is some money than stay here and fight over what is left over.

I wish you all the luck you can get.

 

[seattle smitty]

Thanks, but I had a good dose of reality a couple of days ago. I was feeling a little sorry for myself, for reasons not worth recounting, until I got to talking to a young-middle-aged single mom with whom I have a slight acquaintance. Very nice woman, pleasant and upbeat. But she was telling me a little bit about herself, and about raising her developmentally-disabled daughter, 19 years old, with the mental capacity of a 3 to 5 year old.

Relative to that kind of heartbreak, someone like me has no right to feel sorry for himself. It was one of those slap-in-the-face moments in life that says, "You need an attitude-check, fool!!"