Rolls-Royce 20/25

20/25 1929 - 1936

This became the best selling Rolls-Royce car up until World War 2. The engine was of 3 ½ litres capacity with a cast iron cylinder block and head on an aluminium crankcase. The small-horsepower chassis was now powerful enough to carry large saloon and limousine coachwork.

Production numbers: 3827

Technical Specification

Engine: 6 cylinders, capacity 3699cc. Separate cast iron block and aluminium crankcase with detachable cast iron 6-plug head. Overhead pushrod operated valves. 7-bearing crankshaft with vibration damper. Pressure fed lubrication with relief valve feeding rocker shaft and timing gears.

Ignition system: Independent coil and standby magneto systems. Centrifugal advance with hand override.

Cooling system: Engine driven pump and fan. Temperature controlled by radiator shutters: hand operated with temperature warning lamp, thermostatically controlled from 1932.

Carburation: 2-jet type with starting carburettor and automatic air valve. From 1934, single jet expanding type.

Fuel: 14 gallon rear tank with Autovac. 18 gals from 1932. Hobson Telegauge. Electric fuel gauge from 1932.

Transmission: 4-speed gearbox in unit with engine. 1932, synchromesh 3rd and top. Right hand gearchange. Single dry plate clutch, 1936 Borg and Beck type. Open drive propeller shaft. 1936 Hypoid spiral bevel final drive introduced.

Suspension: Semi-elliptic leaf springs front and rear. Hydraulic dampers, equipped with Ride Control from 1934.

Brakes: Internal expanding 4 – wheel operation with independent handbrake on the rear wheels. Mechanical servo motor driven from the gearbox.

Steering: Worm and nut. 1936 Marles cam and roller steering box

Chassis lubrication: Oil gun and part centralised system. ‘One-Shot’ centralised chassis lubrication system from 1932.