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Rolls-Royce 20/25 Horse Power

The Rolls Royce 20/25 H.P.

The Rolls-Royce 20/25 built between 1929 and 1936 succeeded the 20hp as Rolls-Royce’s “small car”.

The in-line 6 cylinder overhead valve engine was similar to that used in the 20HP but was enlarged to 3699 cc by increasing the bore from 76 mm to 82 mm with the stroke remaining at 114 mm. A single Rolls-Royce carburettor was used and both coil and magneto ignition were fitted. The four speed gearbox was mounted in unit with the engine and a traditional right hand change used. Synchromesh was fitted to third and top gears from 1932. (Chassis numbers GKT 32 onwards)

The substantial chassis had rigid front and rear axles suspended by half elliptic springs with braking on all four wheels assisted by a mechanical servo. Separate rear brakes were fitted for the handbrake. The famous Rolls-Royce radiator with triangular top was used with vertical louvres, the angle of which could be adjusted to control engine cooling. To begin with, the radiator shutters were operated manually via a lever on the dash; later cars (Chassis GBT22 onwards) were fitted with automatic control via a thermostat.

The larger engine allowed the top speed to increase to 75 mph (121 km/h) but many owners had large limousine bodies fitted to the chassis with the predictable degradation of performance.

Rolls Royce 20/25

The Original Specifications

Engine: A straight 6 cylinders, 3¼” x 4½” 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: a 12v independent coil and standby magneto systems. Centrifugal advance with hand override on the steering column .

Cooling system: Engine driven pump and fan. The temperature controlled radiator was enlarged and fitted with vertical shutters: These were hand operated in the early models and came equipped with a with temperature warning lamp, in 1932 from the GBT 22 range (TB Series) a thermostatically controlled system was introduced.

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

Fuel: 14 gallon rear tank with Autovac and the Hobson Tele-gauge. In 1932 the tank was expanded to 18 gals and an electric fuel gauge was used.

Transmission: 4-speed gearbox in unit with engine. 1932, synchromesh 3rd and top. Right hand gear change. 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 specification: Wheelbase 129″, chassis weight 2650 lbs., tyres 6.00 x 19, From the R series onwards this was extended by 3” to 132 inches.

Peabody’s chassis GHA16 is an A2 series, built in 1933 by Rolls Royce and the coachwork, built by Windovers and delivered in 1934. A2 series chassis have numbers prefixed GBA, GGA and GHA.