Due to its strong, solid, hardened steel construction many excavator operators see no need to regularly maintain their undercarriage. Unfortunately, this is an expensive mistake to make. Just following the below two simple daily maintenance practices will make a huge difference to the life of your excavator undercarriage.
1. Remove packed debris and dry material from the undercarriage
At the end of every day and/or before travelling long distances you must remove any debris and dry mud/dirt/clay (known as packing material) from the undercarriage. Use a short narrow shovel or steel bar. If possible also use water to hose down the undercarriage. If you are not working in rocky/hard ground conditions rather remove roller guards as these also trap debris.
- Dry material on the sprocket teeth increases the track chain tension which greatly accelerates wear (see maintenance point 2 below).
- Packing material acts as a grinding paste between the components and accelerates wear. As an example the hardness of Steel ranges from 5 – 8.5 on the Mohs scale. Certain common materials such as Alumina, Andalusite, Pyrite, Silica and Quartz are equally as hard.
- Dry material prevents the rollers from turning freely which causes the chain to drag across the roller massively increasing roller and chain rail wear.
2. Check track tension
A track chain that is too tight is possibly the greatest cause of premature undercarriage wear. Travelling with a tight chain also puts extra load on the engine, which wastes fuel. For this reason we recommend that track tension be checked at the start of each day, or whenever underfoot site conditions change.
- A track that requires 30cm of slack running at 20cm of slack will experience a 300% increase in wear stress, especially on the bushes and sprocket.
- A tight chain prevents the idler from turning freely (packing can also cause this or make this worse). The chain slides over the idler and wears flat spots onto the idler (it begins to look square).
- A track chain that is too loose may come off. Loose track also results in additional shock loads and side to side wear on components.
- Track shoes that move from side to side when making contact with the ground (like a snake) as the excavator moves.
- Wear on the sides of the sprocket teeth (corner gouging).
- Damaged idlers (chips and scratches) caused by the chain snaking about as it moves over the idler.
- Rock guards that feel rough on the inside due to the chain rubbing while the track is snaking.
- Checking the track tension on a Hyundai excavator takes no more than 5-10 minutes a day.
- Raise the chassis on one side using the boom and arm.
- Remove any mud on the tracks and frame by either rotating the track, shovelling or washing.
- Measure the distance – as close to the centre of the undercarriage as possible – between the bottom of the track frame and the start of the track shoe
- Compare the actual distance measured with that on chart below and decide whether to tighten or loosen the track chain.
- Turn the grease nipple 1 turn to the left to release grease and reduce track chain tension
- Use a grease gun to add grease to tighten the track chain
Recommended track tension on common Hyundai excavators:
The above track tension measurements reflect average ground conditions.
- For hard/rocky ground increase track tension slightly (i.e. slightly less distance).
- For soft/muddy ground decrease track tension slightly (i.e. slightly more distance).
3. Inspect the undercarriage
Inspect the entire undercarriage for problems and take remedial action if required.
Stand in front of the machine:
- Look down along the tracks to see if there is a section out of line.
(This indicates a loose track shoe or broken link pin)
Stand to the side of the machine:
- Look across the rollers to make sure all are present and in alignment.
Walk up to the machine:
- Look for loose track shoes (adds wear to pins, bushes and sprockets)
- Look for chipped sprocket teeth (accelerates wear on bushes)
- Look for loose or missing sprocket bolts.
- Check bottom rollers, track guides, top rollers – for loose or damaged areas
- Check rollers, idlers and final drives for oil leakage (reseal before internal damage occurs)
4. Every 1 000 hours measure the undercarriage for wear:
Undercarriage wear is not simply a factor of how much material is left on a component. To understand undercarriage wear you also need to consider that:
- All components are surface hardened to a certain depth to resist wear. Once this hardened material is worn away the component is considered 100% worn. At this point the component should be replaced or rebuilt, even though it can still be used. However, if used after this point wear will increase quickly until the component fails (this will also increase wear on related components).
- As rollers and idlers wear their diameter decreases. This means that they turn faster while in use which accelerates wear.
- As the pins in the track chain wear the pitch (distance between each pin) of the chain increases. This results in the bushings and sprocket teeth not meshing together smoothly which increases wear on both the sprocket and bushes.
- A worn sprocket also has a smaller diameter – which extends the pitch of the sprocket and results in the bushings and sprocket teeth not meshing together smoothly which also increases wear on both the sprocket and bushes.
You also need to consider that excessive wear on any one component of the undercarriage will cause wear on all other components – as they work together as a system. Therefore it is best to rebuild/replace chains, rollers and sprockets together – as matching new and used components results in excessive wear on the new component.
Based on the above you can see that checking the amount of wear on an undercarriage and making a decision as to whether to replace/rebuild/run to destruction at any point is not an easy task. It requires some skill and some judgement.
We therefore recommend that every 1 000 hours you call your OEM dealer or a specialist undercarriage company and ask them to check that undercarriage wear is still within acceptable limits and obtain their advice on the wear levels of the various undercarriage components. You should receive a report on chain link wear, sprocket wear, roller wear, idler wear, external bushing wear, internal pin wear and grouser shoe wear.
Also ask the OEM Dealer to give you a report on your excavator usage (recorded on the machine ECU). Look at parameters like, total hours spent travelling vs digging, total hours travelled in High Speed Mode vs Slow Speed Mode.
Finally, every 1 000 hours, you should also check the torque settings on all of the bolts on the undercarriage (roller and top idler brackets, track shoes, sprockets and final drives).