Work through the undercarriage in order of likelihood: track tension first, because a loose chain is the most common cause by a wide margin; then sprocket tooth wear, because hooked teeth stop meshing with the bushings and let the chain climb; then bushing stretch, roller flange wear and idler alignment. A derailment on one side only points at asymmetric wear, and a derailment that began after undercarriage service points at reassembly. Adjusting tension without checking wear buys days, not months, so inspect while the machine is up on blocks.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Track throws when turning sharply or reversing at speed | Loose tension or worn sprocket teeth. These two operating conditions load the mesh hardest. |
| Derails only over rough or stony ground | Guide guards, idler alignment or roller flange wear. The chain is walking sideways before the obstacle finishes the job. |
| Clacking or climbing noise at the sprocket before it derails | Stretched bushings no longer seating in worn teeth. The sound is the mesh slipping a tooth. |
| Started after undercarriage work | Idler or roller refitted out of line, or tension set with packed mud giving a false reading. Service history changes the order of the inspection. |
| One side derails, the other never does | Compare the two sides. Asymmetric wear in sprocket, bushings or flanges shows up exactly this way. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Track tension too loose | The dominant cause. Sag measured at the mid rollers beyond the manufacturer's figure lets the chain climb the idler on reversals and tight turns. |
| Worn sprocket teeth | Teeth wear into hooked, pointed profiles that no longer seat the bushings. The chain rides up under load and derails at the sprocket first. |
| Stretched pins and bushings | Wear lengthens the chain pitch. The longer pitch no longer matches the sprocket, and the mismatch accelerates both parts. |
| Worn roller and carrier roller flanges | Flanges hold the chain centered. Wear them away and the chain walks sideways until something lets it off the frame. |
| Misaligned idler or worn guide guards | After front idler work, or simply from guard wear, the chain loses the guidance that kept it square to the frame. |
| Operating habits | High-speed pivot turns, spinning in soft ground and fast reverse all throw chains on machines whose tension and wear are already marginal. |
How to confirm it
- Lift the machine and measure track sag
Raise the track clear, let it settle, and measure sag between the mid rollers against the specification. Mind packed mud: it fakes a tight track that is actually loose once the machine works and shakes it out.
- Inspect the sprocket tooth profile
Look for hooked, pointed or asymmetric teeth, and a step at the root where the bushing used to seat. Take a photo for the parts desk; tooth profile is the fastest wear evidence there is.
- Check bushing wear and the mesh
Measure outside diameter on the bushings where they run and compare against the unworn section under the track. Then watch the mesh with the sprocket while the track is crept one revolution.
- Inspect roller flanges and link side wear
Flange height, and wear polish on the sides of the links, tell you the chain has been walking. Chase the direction of the walk toward whichever roller or idler started it.
- Check idler alignment and guide guards
With the chain off or slack, confirm the idler sits square to the frame and the guards still have their section. Alignment after any undercarriage service is worth an explicit check, not an assumption.
- Reset tension and review the operating pattern
Adjust to specification with the track clean. Then talk with the operator about turns and reverse speed, because habits repeat the fault on repaired machines as reliably as worn parts do.
What to do about it
Tension out of specification with sound sprocket and bushings: adjust and monitor. Recheck after a week of work, because a track that will not hold its tension has a leaking grease valve or an idler seal to find.
Sprocket teeth hooked: replace the sprocket. Fitting new chain to worn teeth, or leaving old chain under a new sprocket, makes the mismatched pair wear out at the speed of the worse half.
Bushings stretched past the limit: turn the pins and bushings where the design allows, or replace the chain. Measure before deciding; the 180-degree rotation buys real life only when the wear is on the running surfaces only.
Roller flanges or idler worn: replace the affected rollers and re-align the idler, then find what caused the walk. Replacing parts without finding the alignment fault invites the same wear again.
Whatever the outcome, Guangzhou Shenyue Machinery Technology Co., Ltd. supplies sprockets, rollers, idlers and complete track from Guangzhou, with 3,000+ part types on the shelf and 100,000+ part numbers available to order, and each quotation line stated as genuine, OEM-quality or aftermarket.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Sprocket | Genuine; OEM-quality. Replace with heavily worn chain, not independently of it. |
| Track chain, pins and bushings | Genuine; OEM-quality; aftermarket from known makers. Measure before choosing rotation over replacement. |
| Track rollers and carrier rollers | Genuine; OEM-quality. Match flange section to the machine series. |
| Idler assembly | Genuine; OEM-quality. Confirm alignment on installation. |
| Track adjuster grease valve kit | Genuine; OEM-quality. A valve that seeps is a tension fault that returns. |
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
How tight should the tracks be?
Tight enough that sag at the mid rollers is within the specification in the manual, and no tighter. Over-tensioning loads the front idler, the bushings and the final drive, and buys nothing against derailing that correct tension and sound parts would not buy better.
Can I fit a new chain and keep the old sprocket?
You can, and it is a common false economy. The worn tooth profile chews into fresh bushings immediately, and the chain that was bought to last arrives at half its life within months. Pair major undercarriage replacements on wear, not on the calendar.
Does a derailment itself cause damage?
Frequently. The chain can cut hoses, bend guards, score the idler and challenge the frame. After any derailment, inspect the undercarriage before simply re-tensioning and carrying on, because the derailment may have been the symptom of something that is now also the casualty.