Read Wear Clues To Save Track Hassles

Sept. 28, 2010


Feel for Bushing Wear
Feel for Bushing Wear


Poor maintenance of track-chain tension shows up quickly in bushing and sprocket wear on most crawler undercarriage. That's why being able to do a quick, accurate field inspection is such a valuable skill for an equipment pro. If you can identify tracks that are not maintained or operated properly, a little training can cut a big chunk out of a tractor's operating cost.

Construction Equipment spoke with field-service advisor Jeff Sigmon from RDO Equipment, Deere's Texas dealer, at the meeting of the Association of Equipment Management Professionals last October, about the most important clues to watch in undercarriage wear. He said that since the industry has switched to sealed and lubricated pins and bushings there's very little wear within the pin-and-bushing joint when maintained properly. The critical indicator of when to turn pins and bushings, thus the best way to control undercarriage cost, is the ratio of bushing external wear to chain link wear.

"Grab a bushing and feel the thickness to find out what condition the track is in," Sigmon says. "Is there reverse-drive-side wear? Use a caliper to measure bushing wear."

The other leg of all-important chain condition is the height of the chain link. Measure link height as close to the pin as possible. The relationship between bushing wear and link-rail wear determines the condition of the expensive steel in the track chain.

"You want to compare the wear on the hardened surface of the link to the hardened surface of the bushing," Sigmon says. "If you've worn 50 percent of the hardened face of the link and 100 percent of the lower face of the bushing (the face that normally engages the sprocket), it's time to turn."

Of course, the clues are not always so clear cut.

"If you're measuring wet (sealed and lubricated) chain and the link is 40 percent gone and the bushing is at 80 percent, it's not always a good bet to try for 50 percent and 100 percent," Sigmon says. "You'll end up with a lot of dry joints."

He suggests that as the undercarriage components near their wear limit, seals in the track chain are more likely to fail. Dry joints can cause a lot of internal pin-and-bushing wear. Even if you pull the chain apart before the pins become badly worn, the parts cost of your bushing turn will skyrocket.

"You can check for dry joints, but be careful," Sigmon says. "Wet your palm and touch the ends of the pins after the machine has been working a few hours. The dry ones will be HOT. I just got a little infrared temperature gun—I like that method a whole lot better."

Approaching a machine that he knows nothing about, Sigmon says he ignores the hour meter at first. The age of the machine doesn't necessarily relate directly to the condition of the tracks because of the wide variation in wear rates in different operating conditions, and he doesn't want the hour meter to influence his perception of actual wear.

"I check two things right away," says Sigmon: "1) Track tension—or the sag between the forward carrier roller and the idler. If it looks correct, they're probably doing a good job maintaining the track; and 2) I look to see what kind of packing are they getting. Are they cleaning the packed material out regularly? Is there a sharpshooter (as small, narrow spade) on the tractor, and does it look like it's been used?"

Track-chain tension must be checked every day, or when underfoot conditions change. That means after a rain turns the ground muddy, after the mud starts to dry, when the machine moves from clay to sand, or vice versa. Mud packing in the sprocket segments will change the chain tension and accelerate wear. When it starts to pack, you have to loosen chain tension to prevent reverse tip wear on the bushings and sprocket teeth. The Case Undercarriage Manual specifically commands: "Always maintain the correct track tension (a process described in each machine's operator's manual) and always clean the undercarriage when you are done for the day."

"After chain tension, the next thing I always check is the sprocket segments," says Sigmon. "Does the machine have a nice, tall tooth, or is it dished out or sharp-toothed?

"What do the sides of the sprocket teeth look like?" Sigmon asks. "If they're getting worn, the machine may be doing a lot of side-slope work and the chain could be getting snakey. Feel the rock guards to see if they're getting sharp on the inside."

Evidence of serious side wear is less common than variations in bushing and sprocket wear, but determining the causes of side wear can identify wasteful operating habits. Turning repeatedly to one side of the machine or favoring one corner of the blade, for example, can result in improper alignment or wear on bushings and shims that support idlers, rollers, and track frames.

"If you're seeing lots of side wear, sink the ripper and raise the machine up on its blade so that the tracks are hanging free. Then have somebody roll the tracks. Standing down on the ground, you can see if the chain is rolling true," says Sigmon. "Bearings and bushings in the trunion allow the roller frame to float up and down, but idlers should be straight. As trunion or support bushings wear, the roller frame may move side-to-side and you'll get a lot of wear on the shims on either side of the idler. When they get loose like that you may be able to work just fine on flat ground, but if you go to work on a side slope, it can throw the chain.

"On some machines, you can see from the cab the equalizer bar that stabilizes the track frames if you lean out and look down," Sigmon says. "If you lower the blade until the machine starts to tilt back and watch how much the frame moves before the equalizer bar starts to move, that will show you how much wear is in the equalizer bar."

Sigmon recommends consulting the end bits on the dozer blade to find out if the operator prefers turning to one side. The end bit on the preferred side could be worn more than the other. In cases of extreme wear, you'll find more bad pin-and-bushing joints on the preferred side, too. The track chain will typically be more worn.

Each of the manufacturers publishes acceptable measures of wear for each machine model, detailing the limits of bushing, link, and other component wear. Their track manuals tend to offer a wealth of information on how to interpret wear patterns, too. It's required reading for anyone committed to controlling undercarriage cost.

Feel for Bushing Wear


When the undercarriage is clean and chain tension properly adjusted, each bushing seats against the sprocket tooth. Bushings will gradually wear into the forward side of the sprocket teeth. The most economical time to turn the bushings is when this side of the bushings is 100 percent worn, and the link rails are 50 percent worn.

Forward Wear

Reach up under the track chain to check bushing wear, and you'll find the normal forward wear on the lower back side of the bushing.

Illustrations: Case

Reverse Wear

Reverse wear erodes the lower front of the bushing. Reverse tip wear tends to flatten the bushing, but most tracks get enough reverse drive wear to round the edges.

Vertical Wear

Root wear, or vertical wear, is caused by repeatedly shifting from forward to reverse, and takes metal off the bottom of the bushing. It is exacerbated by high chain tension.

Reverse Wear Mirrors Forward

Driving the machine in reverse twists bushings against the sprocket teeth and the front idler. Wear rate on bushings is much faster than forward wear. The pocket ground out of the sprocket-tooth face opposite forward wear is easily distinguished from reverse tip wear, which rounds off the tip of the teeth.

Chain Tension Slows Tip Wear

Tip wear on the reverse side of sprocket teeth happens while the machine is driving forward. Sprockets packed with mud force the bushing to seat high on the tooth, and a single bushing carries nearly all of the drive power. Following bushings strike the back side of the teeth, rounding off the tops and reverse side. Loosen track tension to reduce some wear. Relieved sprockets can allow mud to squeeze out of the sprocket roots.

Quick Tip: Measure Link-Rail Wear

With a depth gauge, measure link height from the rail surface to the track shoe. Hold the gauge as close to the end of the pin as possible, making sure the link and shoe surfaces are clean.

Illustrations: Case

When to Replace Sprockets

Worn sprocket teeth are pointed, with greater distance between drive surfaces (pitch). The only time you should mix new undercarriage parts with worn parts is when pins and bushings are turned. The turn returns chain pitch to original dimensions, so sprocket segments should be replaced to match. All the components will last longer.