Key points
- Choose the meter that matches the wear: hours, kilometres or calendar time. One asset can need more than one.
- Schedule against fixed milestones. A 250 h service done late at 285 h still leaves the next one due at 500 h.
- At a milestone where several intervals meet, do the largest one. At 1,000 h the 1,000 h service is due, and it includes the smaller ones.
- Meter-based schedules are only as good as the meter readings. Read meters on a fixed routine.
Pick the meter that matches the wear
An interval is a promise that a component will be inspected or replaced before it wears out. It only keeps that promise if it is counted in the same unit the component wears in.
| Trigger | Use it for | Typical examples |
|---|---|---|
| Run hours | Engines, hydraulics, compressors, generators | Excavators, loaders, gensets, pumps |
| Kilometres | Drivetrain, brakes and tyres on road vehicles | Trucks, vans, light vehicles |
| Calendar | Things that age or are regulated whether they run or not | Fire systems, lifts, HVAC filters, pressure vessels, cold rooms |
Many assets need two triggers at once. A truck that sits idle still needs its annual inspection; a generator that runs around the clock needs its oil changed long before the calendar says so. The rule is that each trigger is judged on its own, and whichever comes due first is the one that is due.
Fixed milestones versus a rolling countdown
There are two ways to work out when the next service is due, and they give different answers the moment a service is done early or late.
- Rolling countdown: next service = meter at the last service + interval.
- Fixed milestones: services fall at fixed points on the meter (250, 500, 750, 1,000 h), the way manufacturers write their schedules.
Worked example: a machine on a 250 h interval has its first service done late, at 285 h.
| Service | Rolling countdown says due at | Fixed milestones say due at |
|---|---|---|
| 1st (done at 285 h) | 250 h | 250 h |
| 2nd | 535 h | 500 h |
| 3rd | 785 h | 750 h |
| 4th | 1,035 h | 1,000 h |
With a rolling countdown, one late service re-phases the entire programme. Every service after it is now 35 hours off the manufacturer's schedule, and the big 1,000 h service no longer lines up with the smaller ones. Early servicing is the mirror image: a 250 h service done at 240 h should not pull the 500 h service forward to 490 h.
Nested services: 250, 500, 1,000 and 2,000 hours
Most manufacturer schedules are nested: every 250 h an oil service, every 500 h that plus filters, every 1,000 h that plus more, and so on. At any milestone, the service that applies is the largest interval that divides it exactly.
| Meter | Service that applies |
|---|---|
| 250 h | 250 h |
| 500 h | 500 h |
| 750 h | 250 h |
| 1,000 h | 1,000 h |
| 1,500 h | 500 h |
| 2,000 h | 2,000 h |
This is why the rolling countdown causes so much confusion on nested plans: once the services drift off the grid, there is no clean answer to which service is due, and teams end up doing a 250 h service when a 1,000 h one was owed.
Due soon, due and overdue
A schedule is only useful if it warns early enough to plan the work. Give each trigger its own warning window, sized to how fast the meter moves and how long it takes to get parts and a slot in the workshop:
- Hours: a window of around 50 h suits most plant on a single shift.
- Kilometres: around 500 km for vehicles doing regular daily runs.
- Calendar: one to two weeks, longer if a contractor or an inspector has to be booked.
These are starting points, not rules. Treat a machine whose meter has not been read for two weeks as unknown rather than fine: a stale meter is the most common reason a service is missed.
A setup checklist
- Group assets by make and model, and write one service plan per group from the manufacturer's manual.
- For each interval, list the tasks and the parts and fluids it consumes, so the stores can prepare.
- Record each asset's last service and the meter it was done at. Without it, the first due date is a guess.
- Set a meter-reading routine (daily for plant, weekly for vehicles) and stick to it.
- Review overdue services weekly, and record the meter at completion every time.