Managing the undercarriage on a mid-size crawler tractor is a complicated task. There are a daunting array of combinations possible, between the different shoe types and widths combined with different chains and guarding options. There are also issues of monitoring track tension and alignment and measuring the undercarriage to determine proper maintenance intervals.
Because the amount of money you can charge to move a yard of dirt is roughly equivalent to what it was in the early 1980s, undercarriage management is a task that cannot be ignored. “Depending upon the environment, the undercarriage can be the most costly system to maintain on the crawler tractor,” says Dick Schaeffer, Komatsu America. “Depending upon what it is doing, about 40% to 60% of the maintenance costs of the machine are going to center around the undercarriage, and 40% to 50% of the initial purchase cost of the machine will be replaced in the undercarriage. So if you have a $100,000 machine, during its life cycle it is going to consume $50,000 worth of undercarriage.”
But you can control undercarriage cost through many variables. “While wear is inevitable, it is controllable and it is our job to advise the end user how he can extend his undercarriage life,” says Schaeffer.
Improper tension kills
Keeping your tracks properly adjusted is a good place to start. “Track tension is the single most important and yet the most controllable maintenance item on the crawler tractor,” says Schaeffer. “It is reported that for every extra inch of track tension, you add 30,000 psi of tension to the bushing/sprocket relationship.”
“You can sacrifice two-thirds of your undercarriage life just by having the tracks too tight,” adds Tom Neeley, undercarriage commercial manager, Caterpillar.
But track tension constantly changes with the soil conditions. Packing can quickly turn a properly tensioned track into one that is severely tight.
“Track tension should be monitored in actual working conditions,” says David Koester at Berco of America. “Track tension increases if the sprocket and chain become packed with mud, snow or other materials. The track tension decreases as the packing becomes less.” Normal wearing of the track chain may also create pitch extension, which loosens the track. “The track should be adjusted accordingly. The reality is that very few people are good at that.”
Matching the conditions is critical when making the adjustments. “Don’t put the tractor on a clean slab, wash it off and adjust it,” advises Neeley.
“Get out there in the mud and gunk and run it a little bit, then adjust it. You reach a point where you can have proper track adjustment even in a packing environment.”
The weather may dictate that you make several track adjustments throughout the day. “Sometimes people will say it rained this morning,” says Neeley. “It is just really a pain to go and adjust it. Well, we like to say it will adjust itself. You will wear away iron in a rapid fashion. Adjust it if you really want to control your undercarriage cost.”
Schaeffer was previously an engineer for a large contractor and has witnessed the benefits of frequent track adjustments. “I have been on projects where there was a lube truck that just drove around and inspected machines because the operating conditions were that bad,” he explains. “They would pump them out and start running them a little bit loose so they would have room to pack. Then, as they operated throughout the day, they would stop and make sure the track tension was proper.”
If you have to choose between tight and loose, opt for a little bit loose, Schaeffer advises. You not only reduce chain life when it is too tight, but it puts a strain on other components, like the front idler and carrier rollers.