Quite often when looking at the for sale ads I see "Rails 90% sprockets 20%" With a mismatch in wear like that wouldn't that be hard on the newer parts? What happens when you now replace the sprockets and have 85% rails? Is this normal for these parts to wear at different rates, or is it just owners replacing parts at different intervals??? Just trying to continue my education....Thanks
The first thing you need to do is confirm if the percentages are the amount of life left or amount worn. When trying to sell a machine, most sellers will install new sprockets. Sprockets are the first thing most buyers look at when inspecting u/c. To answer your question, No, it is not normal for the sprockets and rails to have that much of a varience in the amount worn. The sprockets will wear rapidly to match the wear on the rails. I would say the sprockets were replaced recently.
The % is supposed to indicate the % of life left - so I don't know how "sprockets 20%" equates to, "the sprockets were replaced recently". :beatsme Alll undercarriage components can wear at different rates according to the operating conditions and soil types. Straight-line agricultural work at modest speed, in non-abrasive soils will see minimal rail wear. Thus the sprockets and bushings will wear at a faster rate than the rails in this type of work - resulting in the type of undercarriage wear as itemised in the first post. On iron ore mining, the ore (rock) in its natural state is exceptionally abrasive. Surprisingly, the iron ore when broken up and powdered has little abrasive ability. As a result, tractors working on iron ore can have track shoes at 5% or 10% after as little as 1000-1500 hrs - but the sprockets, rails and bushings will show very little wear, and still be around 95%. Crawler tractors working in wet sandy clay conditions have amongst the highest undercarriage wear rates. The only thing worse for undercarriage wear, is working in water containing fine sand. You can replace sprockets and pins and bushings, with worn rails, and still have satisfactory undercarriage. In the old days of dry track chains, my tractors would wear out 2 sets of pins and bushings and 2 sets of sprocket segments, for every set of links. I would get around 1500 hours out of a set of dry pins and bushings, whereby they would then be turned. At 3000 hrs, the pins and bushings would be replaced and new sprocket segments fitted. Sometimes, I'd run some weld on the rails at this time if they were less than 50%. Back in the days of dry track chains, it was economic to run weld on the links to build them up again. Once the rebuilt undercarriage was reinstalled, I'd run another 1500 hrs before doing another pin and bush turn. Once that turn was done, the entire undercarriage was then run to destruction at around 6000 hrs - because at that stage all components - rollers, rails, sprockets and pins and bushings, were at 0%. Sometimes, on the right kind of work, I could get another 10% or 20% out of the undercarriage, taking it to 120% worn. At that point, I often had trouble keeping tracks on, and loading up onto a trailer (climbing ramps) became an interesting exercise, as the sprockets often jumped the bushings (due to sprocket teeth being just nubs) and the tractor would be struggling to drive up the ramps. Nowadays, with sealed and lubricated undercarriage, it's rare to replace bushings and sprockets, and no-one builds up rails with weld any more. However, seriously worn sprockets and bushings, along with good rails, on SALT undercarriage - often means that the track chain and sprockets need to be discarded, even if the rail height is still good. This is because it is no longer economic to replace badly worn pins and bushings, with new ones, due to the high cost of the parts and the labor. New chains are usually the cheapest way out. If the track rollers are still above 50%, you can usually fit new chains to the worn rollers. If the roller wear becomes a problem later on - as the roller flanges start to hit the pin bosses - then you can always trim the roller flanges with the gas axe.
Very Nice...Couldnt have written it better myself.
OzDozer, Oz might be a little different but I have spec sheets from local OEM dealers that give the customers the % worn. As I previously stated, confirm if its the % worn or % left. Good Luck
QuickTrax - O.K., my error - yes, a quick double check on the Cat undercarriage books shows that Cat does refer to "% worn" as their % measurement. The "%" quoted can be very confusing, as many sellers, refer to "undercarriage %", as the % of life left.
Very informative posts guys thank you....I kinda thought that the % figure was expressed as life remaining on the components. So I see it's very important to clarify how the wear is expressed.
sstocker31 - Possibly the most important feature involved in "undercarriage %" figures, is measured wear. To obtain precise figures on the % of wear, all of the undercarriage components have to be carefully measured, and the current measurement compared to new measurements of the particular component. Cat provide precise dimensions for all new undercarriage components so you can compare exactly, the worn component against new. Sizeable numbers of people "eyeball" undercarriage wear, and take "an educated guess". You can guess all you like on undercarriage wear - but measured wear is what provides the precise answer. Many times, various undercarriage components will show an increased amount of wear when carefully and accurately measured - as against "feeling the wear" with a hand, or "eyeballing" the wear, and taking an educated guess at the % of wear. Rails and rollers tend to wear from a flat profile to a rounded profile. This in itself isn't a huge problem - but a rounded profile will bring roller flanges into contact with pin bosses much earlier, than if the profile stays relatively flat. Improved steels and improved hardening processes over the last 20 or so years has led to rails keeping their profile shape much better, as they wear, than they did previously. This is one area, where often, aftermarket undercarriage fails to deliver the same life as genuine undercarriage - because the steel quality is just a fraction lower, and hardening is not as deep or as thorough. So, you have to examine any machine you might be looking to purchase, as to whether it has genuine or aftermarket undercarriage. A tractor with genuine undercarriage is always worth a little more, because it shows no compromise on replacement costs. In addition, there are owners who "mix/n/match" undercarriage. These are the worst tractors of all to examine, because their undercarriage shows confusing wear patterns. When I speak of "mix/n/match", I'm speaking of large operations where track chains are swapped between tractors - or where an owner has purchased some used undercarriage components and placed them on the tractor. With this type of undercarriage replacement/repair, you can end up with seriously mismatched undercarriage components, that will not perform to their best. One typical example is an owner purchasing several new or good used rollers and installing them on the tractor. The roller profile no longer matches the link/rail profile - thus shortening roller life - and in the case of placing new rollers with worn ones, the new rollers will end up carrying an unacceptable amount of load, and possibly fail much earlier than they should. By far the worst condition to encounter with worn undercarriage is the roller flanges hitting the pin bosses. Once rail and roller wear becomes severe - or the roller wear profile becomes very rounded - the roller flanges start to impact the pin bosses. Once this happens, this is very destructive to both undercarriage and the track frame. Roller flanges hitting the pin bosses results in distorted pin bosses that usually result in the pins becoming loose. Once this happens, the track chain is scrap. Roller flanges hitting pin bosses results in constant hammering impacts on the roller and the track frame - often resulting in broken roller bolts, broken track frame component bolts, and track cover guards falling off.
OzDozer.....Thank you for your contributions to this thread, you explain things very throughly and it really helps us newbes understand the things to look at (and measure!!!) while considering a machine. I did know about measuring wear, but I had'nt considered looking for mismatched components (OEM/Aftermarket) while examining a machine. I have seen several machines with welded up rollers and idlers along with newer looking components mixed with older stuff. It makes sense that accelerated wear will occur with mixed components. Now one thing I would like to clear up in my mind is rails/chains....I understand they are one and the same, and that the mixed terminology is used all the time....is that correct?? Thanks again for everones help!!!
Pretty much everyone in the US calls them rails. I have never figured out why. The rest of the world seems to call them chains or what the Parts Manual calls them which is in fact a [Chain] Link Assembly ........ Just to add fuel to the fire. Most of you know I work in mining so we see wear patterns due to highly abrasive material that maybe your average run of the mill owner or operator will not see. We try to balance out wear on the complete undercarriage system as much as possible, but when only certain parts of the system suffer really high rates of wear it's hard to do that at times. Our tractors basically take out track shoe grousers in short order and apart from that generally the only major wear item is sprockets, but not in all cases. I'm just looking at the report for a D10 with original undercarriage 4100 hours from new. 20% wear on links & bushes, 12-16% on idlers, 6-12% on track rollers, 10% on sprockets, and 56% on track shoes ............. The same tractor at 6100 hours. 45% wear on links & bushes, 24-28% on idlers, 20-22% on track rollers, 30% on sprockets, and 99% on track shoes ............. The simplest fix IMHO for that tractor is a replacement set of track groups, maybe new or maybe used link groups simply with rebuilt grousers on the shoes, and throw them straight on with existing sprockets, idlers & track rollers. Maybe swap some track rollers around from front/rear to the centre & vice versa but I would not get hung up over it if it didn't get done. In theory the optimum solution would be keep the link groups on the tractor and simply replace the shoes, but when downtime costs lots of money it's hard to keep a tractor in the shop and replace shoes one at a time when you could just as easily drop a pair of track groups off and stick another pair on in a tenth of the time.
sstocker31 - Well, the problem is, that local terminology for component description often varies from region to region, and country to country. A typical examples is that "pads" is common terminology in the U.S. for track shoes. In Australia, "track plates" is a common term for track shoes. I try to use the correct manufacturer descriptions for components - so, that way, there's no major confusion when you go to order parts. Caterpillar are very pointed with training for parts people, that correct parts description terminology is learnt and always used, to eliminate confusion and incorrect parts ordering. Basically, a track chain is the complete, assembled set of links, pins and bushings. In, say, a 38 link chain, there is actually 76 individual links, as there is one RH and one LH link in a link set. The rail is the machined flat surface the track roller rolls on. Here's a diagram of the older style, flat track, dry track link, outling the manufacturers descriptions of the various parts of the track link. The newer high-track tractor, track links, are basically the same, but the sealed and lubricated track design has a slightly modified design of link for the lubricated pins and bushings. http://i45.tinypic.com/2mq0twi.jpg Here's a diagram of the entire, older-style Cat flat track undercarriage, showing all the individual major undercarriage component names. The rib on the standard crawler track shoe is designated the "grouser". There are usually numerous different track shoes available - in width, in the number of grousers, and in the thickness. Extra-thick track shoes with a higher grouser, are designated "extreme service" shoes, and are used where shoe and grouser wear is extreme, as in the application that Nige describes above. In the 1930's to the 1950's, there used to be a huge range of track shoes available for the old Cats. They ranged from ice shoes, to rubber pad shoes, to cast steel shoes, and probably a dozen other varieties of pattern. Nowadays, the variety of shoe design choices has been reduced substantially,and it's rare to see much else besides the standard track shoe. http://i49.tinypic.com/2nq8cw9.jpg
OzDozer, I have to tell you your replys above are excellent.
Oz, We actually use Super Extreme Service (SES) shoes and our latest project is to try some with the grousers protected by sprayed-on chromium carbide overlay, Cat call it "ARM wear protection". We just had a D10 working in a really abrasive area of the operation that took a set of new grousers from 100% to replacement in 500 operating hours .......
I believe it's in referance to rail road rails hence the term track layer in which a crawler carries and lays down it's own track with rails for flanged rollers to run on.
That makes sense. Thanks Dan.
Yup... that's the way it started. http://en.wikipedia.org/wiki/Richard_Lovell_Edgeworth http://en.wikipedia.org/wiki/James_Boydell http://en.wikipedia.org/wiki/Tractor_crawler#History It more or less ended up here: http://en.wikipedia.org/wiki/Continuous_track http://en.wikipedia.org/wiki/Crawler-Transporter http://en.wikipedia.org/wiki/Bagger_288 OCR... :cool2 ← lol
The description of tracks as "rails" goes back to the earliest Caterpillar advertising. Here's a salesmans booklet from Sept 1936, designed to show prospective tractor buyers just how the Cat track worked, and how it was far better than any wheeled tractor. http://i45.tinypic.com/2vt5ufn.jpg