The MGB starter motor changed at several points across the production run. The original inertia type was fitted to 3-synchro cars to 1967, using a Bendix-drive engagement mechanism. A pre-engaged type replaced it from 1968 to 1971, with the Lucas 2M100 pre-engaged unit fitted from 1972 onwards. The M418G pre-engaged model is notably large and requires the engine to be jacked before removal, while the later 2M100 is smaller and may be removed with the engine in situ, a practical distinction worth knowing before starting work.
All starters were painted engine red to 1971 and black thereafter. The two starter types use different engagement mechanisms and are not interchangeable. The inertia starter is available as a geared high-torque unit and on exchange. The pre-engaged starter is available in standard, remanufactured, reconditioned, geared high-torque, micro, and slimline specifications.
Starter brush kits are available for both the M418G and 2M100 types. Solenoids are available in three variants, square inertia type, push-button, and pre-engaged for 18V and V8 engines. When a starter fails to crank, the sound on turning the key is the most reliable diagnostic pointer. A single light click indicates the relay or its wiring.
A heavier clunk without cranking points to the solenoid. No sound at all points to battery condition and earth connections first, the engine-to-body earth strap is a frequent culprit.