When the rest of the world is basking in the glow of the holiday season, smart equipment managers think about the condition of their dozers’ undercarriages. Whether it’s simply turning the pins and bushings or replacing worn or damaged parts, the slower work pace makes winter the best time to tune up.
Half of a dozer’s maintenance cost is wrapped up in its undercarriage. And while most of its service requirements can be monitored by sophisticated sensors and tracked through a telematics program, undercarriages don’t yield their iron secrets to high-tech approaches. You monitor them with your eyes and your hands, and when you need to be exact, with gauges and dial calipers.
This makes undercarriage wear a big deal when it comes to decisions about buying or selling used equipment. Get this wrong and you leave a lot of money on the table. Knowing how and why undercarriages wear and how to evaluate that wear is key to nailing your dozer owning and operating costs.
All the components in a dozer undercarriage are designed to wear out together at roughly 4,000 hours, or half the service life of the engine. A midlife tune-up typically happens at 2,000 hours when the pins and bushings need to be turned.
Applications determine what parts of the undercarriage wear out first, says Tim Nenne, senior market professional for undercarriages at Caterpillar. In some cases, the bushing and sprocket segments are the first to hit a service point. In hard rock conditions, shoes will likely be the first point of service.
The most accurate way to determine when a bushing turn may be required is to measure the bushing and sprocket wear, says Nenne. Once the wear is known, a discussion of whether a bushing turn is required to get the maximum hours out of the link/roller system should be held. If a bushing turn maximizes the link/roller system life and makes sense for the cost per hour, then you can determine the best time to do this maintenance.
As long as you have the dozer in the shop at the 2,000-hour mark, it might also make sense to replace the sprockets if they are worn, says Derek Ruell, aftermarket supervisor for Berco America. “The front and rear rollers may be worn more than the center rollers, so you may want to swap those out by taking the front and rear rollers and putting them in the middle and putting the middle rollers on the front and rear, just like rotating tires on a car,” he says. Also look at the carrier rollers, although those can run until they fail and only cost about $100 to replace.
How they wear
In normal operations, the application and underfoot conditions are the largest determining factors for the life of an undercarriage, says Nenne. For example, soils with a high percentage of quartz and high moisture levels will significantly shorten the life of an undercarriage. Quartz is an abrasive material, and the moisture in the soil turns it into a kind of lapping compound.
And while you can’t do anything about the soils you work in, there are many things you can do to minimize wear or damage to an undercarriage. These operational tips start with a jobsite analysis. Unexpected wear is often caused by a new experience – new motions, forces or a new environment, according to Larry Bergquist, staff engineer, undercarriage, at John Deere Construction & Forestry. These might include:
• New jobsite or cutting/grading/pushing at a new depth on a jobsite.
• Jobsites that require longer push distances or jobs that require high-speed reverse travel direction.
• Jobsites that require more turning.
• Additional bench cutting operations (uneven loading and excessive material in the undercarriage).
• Changes in soil moisture content.
Though these are new conditions, they don’t have to be unexpected. If operations does a thorough analysis of the jobsite and identifies these additional wear factors, the cost can be built into your owning and operating figures and bid models.
Also make sure you have the right dozer for the job. Always use the narrowest shoe possible, says Russ Reeg, senior engineer, undercarriage, Deere. A low ground pressure dozer will have a tough time of it in rocky soils. Likewise, a narrow gauge track will bog down and jam with mud and debris in soft soils. Consider changing your fleet mix or leasing the right dozer for the job if necessary, he says.
Frame and alignment issues
Like the tires on a car, the tracks on a dozer have to be aligned to prevent abnormal wear, says Ruell. “You could have an alignment problem. It could be an equalizer bar or a pivot shaft. If your roller frame is off on one side or the other, the tracks will follow the path of the roller frame and cause excessive wear,” he says. “And failure in one part can lead to troubles in the whole. If you have a roller or an idler out and you continue to run it, that can cause a lot of stress on the undercarriage and increase the wear.”
The visual indicators are often obvious. “If the roller frame is cocked out a little bit, you can see it,” says Ruell. “In a recent field inspection, we pressure-washed the undercarriage and had the operator use the blade to lift the tracks off the ground with a six-way blade and tilt it to one side and the other. As it lifts you can see the tightness in the equalizer bar and the pivot shafts. If there is any movement at all, that’s going to cause excess wear.”
Even flat on the ground, there are obvious signs to watch for, Ruell says. “Take a look at your front idler, your carrier rollers and see if those are wearing abnormally. Your sprocket is a good indicator, too, if it is wearing on one side more than the other.”
It’s important to actively manage track sag on crawler dozers, says Bergquist. Soil types, moisture conditions and the work your dozer is doing change over time. When track sag is insufficient, the contact forces are much larger and lead to accelerated wear, he says.
Failure to clean out debris and packing in the undercarriage and between the undercarriage and frame should be corrected in the field, says Nenne. If the application tends to produce packing and the machine is not set up correctly, the packing will lead to unexpected wear.
Another area sometimes overlooked is the guiding and guarding of the undercarriage, says Nenne. If the amount of guiding or guarding is not correct for the application, it will contribute to abnormal wear, he says. Excessive amounts of dirt, clay and debris in these conditions can also hide grease leaks due to faulty seals or cover up grease zerks.
Since your operator spends more time with the machine than anybody, he or she should be trained in proper operation, says Bergquist. Some suggestions:
• Reduce track slippage. It’s not productive and it accelerates wear.
• Limit high-speed travel. This increases the load on the undercarriage without adding any productive value.
• Limit backdragging. It causes more wear than going forward.
• Plan turns. Make them smooth and balanced right to left.
• Plan each pass. Where possible, avoid working on top of crowns, in depressions and across side slopes, as these increase load and often wear one side more than the other.
Inspections of used equipment
Knowing how to spot undercarriage problems can be a skill worth developing.
“The first thing you want to look at is the sprocket,” says Ruell. “The sprocket is going to tell you just about everything you want to know about the undercarriage. If it is sharp, it means it’s been wearing. If it’s not sharp, then maybe they replaced it.
“Does the undercarriage look as though anything has been hitting it? Because you can definitely tell when the pins are sticking out through the track chain and your pin bosses are worn out.”
Another tip is to put your hand under the chain. Feel the pin and bushing. How much wear is on it? If there’s just a little bit of wear, you can feel with your fingers – you’re good to go. If it feels like its egg-shaped, then it’s ready for a turn or it might be junk, says Ruell.
Inspections by trained service professionals
All OEM equipment dealers have trained professionals that do undercarriage inspections and evaluations. Technically, it is possible for a contractor to buy a tool kit and take these measurements themselves, but you’d also need training and a thorough familiarity with the specs. The professionals who know this stuff cold can help you plan undercarriage replacements or repairs to minimize downtime and financial impact to your company.
For these reasons, 99 percent of contractors rely on the dealer to do the inspections and make recommendations, says Ruell. This can often be a free service package that comes with the sale of a dozer. Inspections should be done every three to six months, depending on the hours and wear factors.
Although visual inspections and observations are helpful, the measurements taken by a professional service rep allow you to compare the wear balance and wear progression with your past experience, says Bergquist. This critical analysis of the wear rates provides insight to alter items that are in your control and to improve your undercarriage wear experience before it affects your uptime and profits.
Keep in mind that while a trained professional is best for undercarriage inspections and evaluations, replacing a whole undercarriage or its various components can be done by almost any competent mechanic, says Ruell. “It’s really just nuts and bolts.”
(To see how a product support specialist walks through a complete undercarriage measurement and inspection, check out our video from Flint Equipment in Atlanta: https://www.equipmentworld.com/ucinspection/.)
When a dozer goes to auction or on the used equipment market, buyers like to see the undercarriage less than 50 percent worn, says Nenne. A machine with less than 50 percent wear will sell more easily and obtain a higher price.
“If you are at 50 percent of the pin and bushing wear, the rest of the undercarriage should be about 35 percent,” says Ruell. “That means you may have 800 or 900 more hours on the undercarriage before you have to do a pin and bushing turn. Is it worth putting another $4,000 into it? Probably so.”
Distance rather than hours
When establishing your protocols for analyzing and comparing undercarriage wear, Bergquist suggests basing them on distance traveled rather engine hours. There has been a trend across the industry to work at faster speeds and shut down the engine during long idle periods, he says. This has resulted in more distance traveled per engine hour. Keep this in mind as you compare current appraisals to past experience. Many newer units capture forward and reverse distance and even distance at a given speed, he says.