Replacing an alternator

Changing the electrical generator

REGARDLESS of the engine type in our Land Rovers, all models have a means to put charge back into the vehicle battery. Most commonly, that job is done by the alternator. The alternator is driven by the running engine via a rubberised drive belt. The belt turns the alternator’s central rotor, which is effectively a spinning electromagnet which is surrounded by a stator comprising wire coils. This produces an alternating current (AC) which is converted by a rectifier to direct current (DC). A healthy alternator should be outputting around 13.8-14.4 volts. The extra couple of volts produced over the battery’s nominal 12 volts helps ensure the battery is charged and the electrical system has sufficient voltage for most demands.

Alternator issues will be either charging-related, in that it no longer provides sufficient output to charge the battery, or mechanical, in that the internal moving parts wear out, typically bearings. You’ll spot the former as the battery barely holds a charge, and the latter presents as a louder than usual whirring, whining or graunching sound with the engine running.

Series I, II and IIA models originally used a dynamo, which generates direct current (DC), instead of the alternating current (AC) of the later alternator. Dynamos aren’t as efficient as alternators, and are slightly more prone to failure thanks to the less efficient design principle and, frankly, age.

Either unit is usually mounted relatively accessibly, at the top or side of the engine at the front, where it is driven by a belt off the crank or fan pulley.

Identifying the problem

This Rover V8 had started whining over the course of a few months, which suggested bearings were failing, possibly in the belt tensioner, water pump or alternator. Removing the serpentine belt and manually feeling the pulley action on all items revealed the bearings had worn considerably in the alternator, which was feeling almost crunchy in action. Continued use in this state eventually sees bearings lock up, with obvious cascading damage back to the drive belts and pulleys. Water pumps can share the same drive belt, so ignore potential failure at your peril and it could cost you an engine through catastrophic overheating.

Repair or replace?

We generally have a good spares availability for our Land Rovers, in a quality to match our budget. Many common applications will have parts on the shelf ready to ship and fit – but that may not be the case for all, or indeed the best option. Why? Well most towns still have auto electricians who for years have reconditioned both dynamos and alternators as routine work.

Reconditioning involved testing the unit on the workbench and replacing the failed part(s). It is both a cost-effective, and sensible way to go for many owners, as the core part, if original, was made to Land Rover’s production standards. Repairing the core unit means you keep that factory quality of the components, rather than making do with a potentially lower quality of available modern parts which may be produced for low cost, rather to a quality standard. I had the original V8 unit from mine tested, and both bearings replaced.

Here’s how I changed the alternator on my serpentine Rover V8, though the procedure is broadly the same on any vehicle, just perhaps not as readily accessible.