1963 MG MGB Problems: 2 Known Issues

On the 1962-1964 MG MGB 1800 B-series I4 (3-bearing), early MGBs (1962 to October 1964) use the three-main-bearing 18G/18GA B-series. Its crankshaft has a flange at the rear that physically prevents fitting a modern lip seal, so the factory sealed the rear main with a 'reverse scroll' — a machined thread that pumps oil back toward the sump instead of an actual seal. It works only while the scroll and its mating surface are sharp. After decades the crank wears a faint groove and the scroll loses its pumping action, so a few drops always get past, drip out the bellhousing breather hole (which the factory drilled deliberately, knowing it would seep), and mark the driveway. It is not a catastrophic failure, but restorers chasing an oil-tight engine and a clean clutch are constantly frustrated by it.

On the 1962-1967 MG MGB 1800 B-series I4, early MGBs use a Lucas C40 dynamo (generator) with a separate external control box (voltage regulator), and all the dynamo-equipped (Mk1) cars are positive-earth. The dynamo is limited to about 22 amps (the control box holds it to roughly 19-22 amps) and gives little output at idle, so it struggles to keep the battery charged at low rpm, in traffic, or with extra loads (driving lights, electric fan, modern stereo). The mechanical regulator points burn and drift out of adjustment, and the dynamo brushes/bushes wear, giving a dim-charge or no-charge condition. Combined with aged, undersized, deteriorated cloth-loom wiring and corroded earth straps, this is the source of the MGB's 'Prince of Darkness' reputation — flickering lights, slow cranking, and dead batteries.