We are still shopping for an excavator. It is really hard buying used as I realize many or even most machines are being sold "for a reason", and that reason is usually not disclosed so it is like a treasure hunt to find out the truth.... Mostly looking for something in the 25T class but technically 15T would do for now and we are looking at one this small. I am curious if you guys have run into any hard/fast rules the mechanical's life? I realize this can be HUGELY variable depending on many factors but at least for engines and pumps, it seems 8-12K hrs is about the limit in this class, at in my experience. Obviously things happen and I don't assess based on hours, but sellers are happy to say "runs great", then they have 6 empty cans of ether behind the seat and 2 gallons of coolant. I am looking at one newer 15T machine with 11K hrs on it. I would nearly bet it's the original UC and the pads have some bends. Of course I can find nothing local and this all becomes a gamble but curious if you guys have any useful info on hours for a steel track UC of this size?
You can’t go by hours. You have to know what to look for and how to determine if a machine may be weak in some area. I’ve seen machines with 15k hours that were still good machines because they were well taken care of. On the other hand, I’ve seen some with less than 7000 hours that were beat to hell and not worth anything but headaches.
I can vet a UC if I can climb on it, but these days it seems like everyone is just selling at some auction and there are about ZERO machines in my area so the few that are available just sell for stupid money. It is also risky driving all over to look at machines having no clue what they will even sell for. I still still mad about driving 3.5hrs to look at one with a bad engine and high hrs, and I figured surely I could snag it cheap enough as loading a non running hoe is no fun. That girl sold for retail running value! I think I will have to resort to calling some dirt companies in town and hope they have one coming up so I can vet and negotiate.
In my experience with excavators and their undercarriage systems, they have been living a lot longer now than say twenty years ago. The metallurgy is vastly different today. It has changed the wear factors. It used to be 5,000 hours and everything was worn out. Now days I've seen plenty of 7,000 hour machines where the chains are worn out and the rollers still have 40% left. It's common now to just change the chains and run the rest to destruction and get 8,000 to 11,000 hours. That would depend on how many miles the machine has traveled. If you are interested, here is a video showing what to look for.
John, thanks for your input. I am aware of most of the wear indication points of a UC, but in the days of "online" and "bid now", it makes these decisions quite difficult. We will likely have to accept a machine with 8k-12k hours, which I am not that worried about, IF they are represented accurately but as I said, machines get moved down the road for a reason, and the typical response from a seller is "it's a good machine".... That tells me just about nothing and being deeply embedded in the mechanical and service fields, my assessment is usually quite different once I finally get to look for myself. Have you seen much correlation between UC wear for hours and machine size class? At least in my experience, bigger machines seem to track less miles and the UC seems to go longer. I do recall back when that upper management did a shakedown on operators to get them to clean tracks out, especially if it was going to freeze after someone did some nice damage to a big 365 by being lazy. At least on the minis, it seems they drive all over and subject to more track miles. Sure which they would put a speedo on the track system!!!! That would be way too helpful though....lol
The big machines don't wear the link in the same way that mid and small machines do. The swinging and digging for the links apart and you see that with rail spread on the track pins. Once the ends of the bushings come out of the big ends of the links, the rate of track stretching seems to go about one and a half times faster. All the manufacturers use at least one size too small of track chains for the weight of the machine. That's why you see half step models like the Komatsu PC360 or a Cat 325. They get the next larger size carbody and use the smaller house. Bigger carbody with bigger track chains.
I was just talking with my friend about UC life on the phone. He has a 15K hour 315 CAT that is decent, and I am changing out a 9K hour JD 120 that was totally hammered rails. The difference IMO was what you run on. The JD was digging in small round rock that gets in the tracks, and no matter how often you spin them clean you end up breaking some hard rocks with it. That just kills the bushings over the years. I think that is the X-factor on UC life, what you run on. Same with a 12K hour Komatsu series 5 400 I ran for a company that did mostly bridge jobs. It had a really tight upper, and the levees had just beat those tracks to death. On that 9000 hour 120, I am changing 3 out of 14 lower rollers due to condition. The front two are just gone rattling, and one was feeling a little tight. The other 11 were down about 3/16" and even and the bearings felt good. Front idlers still good, top rollers too.
I agree to a point about the material your machine is working in will have an affect on undercarriage life. The biggest factor that I've seen is how many miles your machine has traveled. The other big factor has to do with the size of the machine and the size of the track chains. Big machines force the links to spread on the track pins to the point of loosing the bushing contact in the big ends of the links. Once that happens the links stretch out of pitch exponentially faster. The photo below shows link spread on a 46 ton machine with 7,600 hours on the clock.
The next photo shows the link spread on a 40 ton machine with 15,000 hours and probably its second undercarriage. Both machine were being used for underground utilities. Basically they put pipe in the ground and sometimes are used for stock piling and loading out trucks.
I'll dig out some photos later today that show what happens on logging shovels with half the hours and probably three times the amount of miles.
I would include 3 factors to make the "how long is a piece of string" determination of excavator undercarriage life. In no particular order..... 1. Distance travelled. Walk long distances (on any type of ground) and the tracks will be hanging off in a heartbeat. 2. Ground conditions. Dry/wet, soft/hard, how abrasive.? 3. Is the U/C generally sized appropriately for the operating weight of the machine.?
That 400 had the spread, and cracked links. When I got done digging in a water main with it, I counted 6 cracked links and 2 that had spread significantly. I walked it in a very straight line and it went to auction on the next lowboy ride. I will post up the 120 rail pics tomorrow. The bushings are just hammered gone, exposing the pins. It was running on mostly just pins the last few years when I was gone. I ran this machine last in 2008 when it had 6500 hours on it, and it has been completely neglected since.
The bigger machines are more prone to cracking over long time periods. First, as Nige has brought up, the chains are too small for the weight they are carrying on large excavators. An example would be a 46 ton machine running on D8 tracks that would normally carry 30 tons. I've had to work on PC1000 excavators running on D9 size chains. That's a 200,000 pound machine running on chains designed to run under a 110,000 pound machine. The other part is that excavators don't push dirt. They sit in one place and dig for a bit bouncing on the chains and basically pounding on them like a jack hammer. This causes work hardening and the subsequent changes in the crystalline structure inside the chain links. The running of the chains to destruction is a normal operating procedure anymore. Turning pins and bushings on excavators is not cost effective and neither is turning in the used chains for scrap with any operational life left in them. There really is no way to maintain undercarriage other than keeping the chains adjusted properly and keeping them under the bottom rollers.
Just a couple things I notice around here is people running wide pads which are intended for softer, compliant materials where reduced psf ground pressures are needed. They take those machines onto rocks and such and it not only bends and tortures the pads, its puts tremendous torsion into the rails. I also find these wide track machines are harder to turn and seem to stress the UC more. John, you mention work hardening of the links, what material are they made from? Are you sure this is not more of a fatigue issue?
Cold Forging by link to roller hammering, will see it as dimples on the running faces.
Wider pads are also a great way to ballast a machine a 15 t machine with 18 inch pads have a lot less stability than one with 24 inch pads and performance wise the increased production from a more stable platform makes wear or bent pads negligible Look for a long carriage they wear better
I wouldn't care for the 120 on 18" for sure.
Yup, one we are getting is an LC with the widest pads they made.
I've gone through some of my old photos and haven't found any of the cracks in the links. The cracking doesn't occur on the part that runs against the roller. I happens on the strut in the middle of the link and just behind the pin boss and they usually run horizontal to the rail. I did find some interesting photos though. The first is what you see when using real wide pads. You get a huge amount of torque when trying to turn and that extra stress goes into the link joints.
Can you recognize what is wrong in this photo?
Rail is on reversed
It doesn't look like this.
There's something wrong in this picture too. A little something extra. I think they call them a bushing. Because this is the other track LOL!