In practice, the difference between a four-hour outage and a four-day outage is often a filter. Spare parts planning is unglamorous and it is one of the highest-leverage things a buyer controls, because everything else about reliability is decided by the machine and how it is maintained.
The mistake at both ends is common: holding nothing and waiting for shipment, or holding a warehouse of parts that never get used and eventually expire. The useful middle ground comes from separating parts by what they are for.
Three categories, three different decisions
Consumables
Filters, oils, coolant additives and similar items are consumed by scheduled maintenance. They are predictable: if you know the service intervals, you know the annual quantity. These should be held on site as a matter of routine.
Wear and failure parts
Belts, hoses, seals, batteries, and the sensors and switches that fail without warning. These are not consumed on a schedule; they are held because a failure is disruptive. Which ones to hold depends on how critical the set is and how quickly you can get a replacement.
Long-lead and capital items
Larger assemblies that are expensive and slow to obtain. For most sites these are not held on the shelf. Instead the decision is whether the supplier or a local partner can supply within an acceptable window, and getting that commitment in writing before you need it.
How to decide what to hold
| Factor | Pushes toward holding on site | Pushes toward relying on supply |
|---|---|---|
| Criticality of the load | Hospital, data, continuous process | Comfort or non-essential backup |
| Distance from support | Remote or export site | Urban, supplier nearby |
| Number of identical sets | Several, so parts are interchangeable | One-off unit |
| Storage conditions | Clean, dry, temperature-stable store | No suitable storage |
| Shelf life | Stable items | Rubber, seals, batteries, treated fluids |
| Availability locally | Model-specific parts | Generic industrial items |
Procurement checklist
- Ask for the recommended spare parts list for the specific engine and alternator model, not a generic one.
- Ask for the scheduled maintenance schedule and the consumable quantities per service.
- Ask which parts are model-specific and which are generic, so you know what you can source locally.
- Ask for lead times on the long-lead items and get a commitment in writing.
- Confirm storage requirements and shelf life, especially for batteries, belts and seals.
- Ask for the parts documentation: exploded diagrams and part numbers, at handover.
- Decide whether commissioning spares are separate from operating spares; they often are.
What to put in the RFQ
Ask for a recommended spares list to be quoted as an optional line, with quantities for a stated period. Say how critical the load is and where the site is, because the sensible answer differs completely between a city hospital and a remote mine. If you are exporting the set, raise parts availability at the same time as shipping documentation, since both affect what you can realistically hold. Our notes on fuel return line arrangements for day tank installations cover a related installation decision that also drives parts planning.
FAQ
Should we hold a complete spare alternator?
Rarely, unless the load is extremely critical and lead times are long. For most sites the practical answer is a written supply commitment for the long-lead items rather than shelf stock.
Do spares expire?
Some do. Rubber components, sealants, batteries and some treated fluids have shelf lives. Ask which items on the list are date-sensitive and record the dates when they go into store.
Is one list enough if we have several different generator models?
No, and this is where costs escalate. Standardising on fewer models is usually worth more than any discount on the spares themselves.
Who provides the parts list?
Ask the supplier at quotation stage rather than after delivery. It is much easier to include the cost up front than to raise a second purchase order later.
Should commissioning spares be separate?
Usually yes. Parts consumed during commissioning and testing are typically distinct from the operating spares you hold afterwards. Confirm which is which.
Next step
Ask for a model-specific recommended spares list with your quotation, including lead times. You can review the diesel generator sets and their engine platforms, and request a quote stating the site criticality and location so the list can be sized to your situation.