Excavator Track Tensioner Guide — Rubber & Steel Crawler Chain Tensioning

Track tension is one of the most-overlooked maintenance settings on a tracked machine. Too tight and the undercarriage wears out fast and the hydraulic tensioner ram works under unnecessary load; too slack and the chain jumps the sprocket, the idlers thrash, and you risk throwing a track on a slope. This guide explains how to check, tension and release tension on both rubber and steel crawler chains safely.

Before you start

Carry out the check on a level surface. A side slope gives a false reading.
For rubber chains: slew the upper-carriage by 90° and lift one side until the crawler is free of the ground.
For steel chains: the measuring distance is taken between the carrier roller and the front idler with the chain in normal contact.
Have a clean grease gun loaded with the correct grade of grease (consult your operator's manual — this is usually a heavy-duty lithium-EP grease).
Wear gloves and eye protection. Releasing tension can spit grease under pressure.

Checking rubber crawler chain tension

On a rubber crawler with a hydraulic tensioner cylinder:

Park on level ground and lift one side of the upper-carriage as above.
Locate the tensioner indicator on the side of the cylinder — it should be flush with the cylinder edge in the normal position.
The indicator only leaves the flush position temporarily, when the internal spring is operating during a shock load.
Check the sag of the chain between rollers — the typical manufacturer specification is approximately 20 mm.
Repeat the check on the second crawler chain.

A hydraulic tensioner that has lost charge will show the indicator permanently retracted; the cylinder needs re-charging via the grease nipple.

Checking steel crawler chain tension

On a steel chain machine:

Park on level ground.
Measure the sag of the chain between the carrier roller and the front idler.
The sag should be approximately 20 mm.
Repeat on the second crawler chain.

If the sag is greater than the manufacturer's specification, the chain has either stretched or the tensioner has lost grease pressure — see the next section to re-tension.

Tensioning a crawler chain (rubber or steel)

The hydraulic track tensioner is charged with grease, not hydraulic oil. A normal grease gun is the right tool — there is no separate hydraulic pump.

Unscrew the access cover on the right-hand or left-hand side of the lower roller carrier (or remove the inspection plate, depending on your machine).
Connect the grease gun to the grease nipple on the tensioner valve via the supplied coupling.
Pump grease slowly until the chain reaches the correct tension.
Rubber crawler only: watch the indicator. Tensioning is finished as soon as the indicator leaves the normal flush position.
Move the machine forward and reverse a few metres, then re-check the tension. Repeat until tension is stable.
With new rubber crawler chains, check the tension 2–3 times during the first day of operation. New chains bed in and slacken slightly.
Re-fit the access cover.

Releasing crawler chain tension

You'll need to release tension to remove the chain or to reduce over-tension. Approach this with care — pressurised grease can drain out fast and is hot if the machine has been running.

Slowly loosen the valve at the grease nipple — partial turns only.
Allow grease to drain out until the chain tension is correct (or until the chain is fully slack if you are removing it).
Re-tighten the valve with the grease nipple in place.
Wipe up the released grease and dispose of it according to local regulations — used grease is contaminated with metal particles from the undercarriage.
Move the machine forward/reverse a few metres and re-check the tension.

Common track tension symptoms

Symptom	Probable cause
Track sag much greater than 20 mm	Tensioner lost grease pressure, or chain stretched beyond service life
Track jumping the sprocket on direction reversal	Excessive sag, worn sprocket, or worn rear idler
Track squealing under load	Insufficient grease in pin/bush bores; tensioner over-set
Tensioner indicator permanently retracted	Failed cylinder seal — needs rebuild or replacement
Tensioner cylinder leaking grease at the rod	Worn rod seal — kit available

Compatible machines

This procedure covers the common hydraulic-grease tensioner used on most UK construction excavators and tracked equipment, including:

Caterpillar — 300-series mini, 3xx midi/large excavators
Komatsu — PC mini, midi and large excavators
JCB — 8xxx mini and JS/JZ excavators
Hitachi Construction Machinery — Zaxis ZX series
Kubota — KX, U mini excavators
Takeuchi — TB compact excavators
Bobcat — E-series mini excavators
Volvo Construction Equipment — EC excavator series
Liebherr — R-series

For machines built earlier than the late 1990s, refer to the operator's manual — some used a screw-jack tensioner rather than a hydraulic-grease tensioner.

Related undercarriage guides

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