Generator Spare Parts: What to Keep in Stock

For generators at remote sites, such as telecom stations, even a simple fault like a blocked fuel filter can last for days if the part is not on site. Changing the filter takes about fifteen minutes, but while the part is on its way the facility has to run on batteries or a portable set.

When a generator is out of service for a long time, the cause is usually not a major fault but a small part that is not in stock. In this article we list the parts that should be kept in stock, at three levels, depending on how the set is used.

What decides the stock?

One list doesn’t fit everyone. Ask three questions:

1. How much does the set run? A standby set running a few dozen hours a year and a primary source running 20 hours a day don’t need the same stock.
2. How long does a part take to arrive? A part that can arrive the same day within the city and one that has to cross a border are planned differently.
3. What happens if the set stops? Does a warehouse go dark, or an operating theatre? The cost of downtime sets the size of the stock.

Level 1: Basic service kit for every set

These parts are changed at every scheduled maintenance. Keep at least one service’s worth:

• Oil filter
• Fuel filter and water separator element
• Air filter (with safety element, if fitted)
• Engine oil (in the class and viscosity the engine manufacturer requires)
• Coolant (of the right type and mix ratio)
• Fan / alternator belt

Change intervals are given in the engine manual. Typically, filters and oil are changed at a set number of operating hours or at least once a year; on dusty sites the air filter may need changing much more often. For the maintenance steps, see our generator maintenance checklist article.

Level 2: Critical facilities and remote sites

Here the aim is to have on hand the parts whose failure stops the set:

• Sensors: Oil pressure, coolant temperature, speed (magnetic pick-up), fuel level.
• Electrical: AVR, fuses, starter and fuel solenoid relays, battery charger fuse.
• Battery: Especially on older sets or sets working in hot conditions. We explain why they fail in why generator batteries fail.
• Fuel solenoid / stop solenoid.
• Hoses and clamps: Radiator and fuel hoses.
• Thermostat and its gasket.
• Block heater element: In cold regions.

Level 3: Sets running continuously as the primary source

On a set that runs long hours every day, wear parts are planned too:

• Several services’ worth of filters and oil
• Injector or injector nozzle
• Water pump
• Starter motor
• Turbo gasket kit
• Radiator cap
• Exhaust bellows and gaskets

At this level, two sets usually run in rotation; while one is in maintenance, the other carries the load. The parts list should be drawn up from the service schedule for the engine model.

How many? A simple calculation

To estimate stock quantity, multiply two numbers: how often the part is changed and how long a new one takes to reach you. Example: the set runs 20 hours a day as the primary source, and the engine manual calls for filter changes every few hundred hours. That means a filter change every few weeks. If parts take a month to reach the site, you need at least two services’ worth of filters on the shelf. Add one more for the unexpected; a delivery of dirty fuel, for example, can block filters early.

A standby set is the opposite. It runs a few dozen hours a year, and filters are usually changed by the calendar rather than the hour meter, typically once a year. Here one service’s worth of stock is often enough. What matters is that it is actually on the shelf.

Finding the right part

The most common mistake in ordering spare parts is the wrong part. When you request a part, give:

• Generator serial number
• Engine make, model and engine serial number
• Alternator make and model
• Controller model
• If possible, the number on the old part and a photo

The same engine model can have different part numbers in different production years. That is why the engine serial number matters.

Common mistakes on site

• Buying a filter because it “looks the same”. The thread matches, but the filtration grade or bypass valve is different.
• Topping up the oil with whatever is to hand. Different oil classes get mixed and the engine manufacturer’s specification is no longer met.
• Leaving belts on the shelf for years. Rubber ages; once fitted, it cracks quickly.
• Keeping no stock record. A filter is used and never replaced. At the next fault, the shelf is empty.
• Ignoring the battery’s date. Even an unused battery ages on the shelf and discharges.

Storage

• A cool, dry place out of the sun.
• Parts in their original packaging.
• First in, first out. Write the date received on the box.
• Oil and coolant containers kept closed. Don’t leave opened oil standing for long.
• Batteries are stored as the manufacturer recommends and charged periodically.

Checklist

• Are the engine and alternator serial numbers recorded for every set?
• Is at least one service’s worth of filters, oil and coolant on the shelf?
• For a critical facility, are sensors, AVR and relays in stock?
• Are the purchase dates of belts and hoses known?
• When stock is used, is a replacement ordered?
• Is the part delivery time known, and is the stock planned around it?

Next step

We can draw up a stock list with you based on your set’s engine model and running hours. For a maintenance plan, see scheduled maintenance; for service and parts requests, see our generator service page or contact us.