Inspect the recoil spring and idler with track tension released to specification, and never by loosening the adjuster grease fitting more than one turn, because the spring is preloaded and the adjuster cylinder can release stored energy violently. Measure idler flange height and tread diameter against the wear limits, check guide clearance to the track links, and look for a leaking idler bearing seal or grease weeping from the idler hub. On the spring side, measure exposed rod length at a known track tension or free length with the adjuster released, look for broken coils, collapsed ends and contact marks between coils, and confirm the adjuster relief valve is not weeping. A spring that has taken a permanent set, or shows coil contact at normal tension, has lost its preload and cannot be adjusted back into service.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Track climbs off the idler on turns or in soft ground | The recoil spring is not holding tension, so the track cannot absorb a shock without slackening. Also produced by a seized adjuster cylinder. |
| Track tension will not hold after adjustment | Grease is escaping past the adjuster seal or the relief valve. The spring may be fine and the cylinder the fault. |
| Grinding or knocking from the front idler | Idler bearing or seal failure. Left long enough, the idler shaft wears and the whole assembly is replaced instead of a bearing. |
| Shiny contact marks between coils of the spring | The spring is fully compressed in normal work, which means it has lost preload or the track is over-tensioned. Either way it is no longer absorbing shock. |
| Uneven polish on the inner faces of the track links | The idler is not guiding the chain squarely. Guide clearance or a bent idler shaft, not a link problem. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Spring fatigue or a permanent set after years of shock loading | Springs are consumables in this position. Once the free length has changed, preload is gone and the track relies on grease pressure alone. |
| Adjuster cylinder seal leaking, or the relief valve weeping | Grease escapes slowly, tension drops, and the operator compensates by pumping more grease into a cylinder that cannot hold it. This eventually damages the spring. |
| Idler bearing or seal failure | Water and abrasive material enter past a failed seal, and the bearing fails quickly. Once the bearing is gone the shaft and idler body follow. |
| Track tension set above specification | Over-tensioning to stop a climb-off is the standard response and it is the wrong one. It removes the spring's travel and loads every component in the chain. |
| Packing material carried into the chain | Mud, coal or aggregate packs between link and idler, raising effective tension without anyone changing an adjustment. Common in bulk handling work. |
Inspection points and their limits
| Item | What to judge against |
|---|---|
| Idler flange height | The wear limit in the manual. Below it the chain is no longer guided. |
| Idler tread diameter | Wear limit. Measure across the tread, not at the flange. |
| Guide clearance, idler to link | Specification with the chain correctly tensioned. |
| Exposed adjuster rod length | Specification at a known tension; a change over time means the spring has moved. |
| Spring coils, ends and contact marks | No breakage, no collapsed ends, no contact at normal tension. |
How to confirm it
- Clean the area and read the safety warning properly
Pressure-wash the track frame and idler area so measurements mean something. The recoil spring stores enough energy to kill, and the grease fitting is not a bleed screw: never remove it, and never loosen it more than one turn.
- Release tension as specified and measure the idler
Release track tension to the manual's procedure, then measure flange height and tread diameter at several points around the circumference to catch an out-of-round idler. Record the numbers rather than judging by eye.
- Check the adjuster cylinder, seal and relief valve
Look for fresh grease at the seal and at the relief valve. A cylinder that cannot hold pressure makes a good spring read as a failed one, and this check is what separates them.
- Inspect the spring without dismantling it
With tension released, look along the coils for breakage, for collapsed end coils, and for polished contact marks. Measure exposed rod length. Any of these findings condemns the spring, and none of them can be corrected by adding grease.
- Order against the serial number before taking the machine apart
Recoil springs and idlers differ by undercarriage series, not by model badge, and a spring with the wrong rate is worse than a worn one. Guangzhou Shenyue Machinery Technology Co., Ltd. supplies recoil springs, adjuster cylinders, idlers and idler bearings for common excavator undercarriages, quoted from the machine serial number. Stock is held as 3,000+ part types on the shelf, with 100,000+ part numbers available to order.
What to do about it
Replace a spring that has taken a set A spring with changed free length, broken coils or contact marks is finished. Replace it with the rate specified for that undercarriage, and replace the adjuster cylinder seals at the same time.
Reseal or replace the adjuster cylinder New seals, a checked relief valve, and a pressure test before the track goes back on. This is the repair that stops the cycle of pumping grease into a leaking cylinder every week.
Replace idler bearings and seals as a set A bearing fitted behind a worn seal fails on the same schedule as the one it replaced. Check the shaft for wear where the seal ran, because a grooved shaft will not seal.
Restore track tension to specification Set tension by measurement on level ground with the machine in the specified position, not by eye and not by feel. Write the figure down so the next check compares like with like.
Address the operating cause of over-tensioning If the track was over-tensioned to stop it climbing off, the real fault is the spring or the idler, and the tension was a symptom of it. Fixing the tension alone leaves the machine climbing off again.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Recoil spring | Genuine; OEM-quality. Rate and free length matched to the undercarriage series. |
| Track adjuster cylinder and seal kit | Genuine; OEM-quality. Seal kit supplied to cylinder part number, not to model. |
| Front idler assembly | Genuine; OEM-quality; aftermarket. Flange height stated at dispatch. |
| Idler bearing and seal kit | Genuine; OEM-quality. Matched pairs recommended. |
| Track adjuster relief valve | Genuine; OEM-quality. Cracking pressure verified before dispatch where testable. |
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
Can I just keep adding grease to hold track tension?
For a short while, and at a cost. Grease that keeps disappearing is going somewhere, usually past the adjuster seal or the relief valve, and the spring is being worked without the support it was designed for. Find the leak, because the cylinder is a much cheaper part than the spring and the frame behind it.
How do I know whether the spring or the adjuster is at fault?
Measure both. Release tension to specification, then check whether the cylinder holds pressure and whether the spring shows contact marks or a changed rod length. A cylinder that will not hold makes a sound spring behave like a failed one, and that mistake is expensive in the wrong direction.
Is it safe to inspect the spring on the machine?
With tension properly released and without dismantling anything, yes. Never remove the grease fitting and never back it off more than one turn, and never work in line with the spring axis. A recoil spring that releases stores enough energy to cause fatal injury, which is why the service manual procedure exists and is not optional.