MASCOT March-April 2001

ROADSTER Roadster Notes - Alternative Engines

Bill Haverly

Roadster owners are fortunate in having alternative engines which can be fitted as the original units become increasingly difficult to find, albeit at the expense of the less popular saloon models.

For the three bearing, 1074cc Roadsters (1939-52), the most obvious replacement is from the 1938-40 Bantam, which was adapted for later Roadsters with an SU carb and a more sporting camshaft. Second on the list are the Super 10 engines 1185cc (1938-40) and 1193cc (1946-48). All three blocks are virtually identical but with different bores -60mm (1074cc), 63mm (1185cc) and 63.25mm (1193cc). Manifolds can be changed to suit the particular series, and, using the same mountings, a complete post-war 10 engine, clutch and gearbox unit will drop into a 4-speed Roadster without difficulty. It will also liven up the performance.

4AD owners are fortunate that they have the same basic engine as the SM1500 Saloon (1949-54), although the gearbox cannot be effectively used. The engine will fit without modification from early 1951 (Chassis No D122U), but the exhaust manifold will need to be retained if the original downpipe is to be used. Watch out also for extended dynamo brackets on pre-1951 engines which cause the dynamo to foul the bonnet side panel. This can be rectified by a relatively simple mod.

The last but not least donor is the 1954-56 Hunter saloon, which had the most developed SM1500 engine, the only drawback being that on LHD 4ADs, the horizontally mounted oil filter fouls the steering column and a mod is required.