The 3 ½ litre was replaced by the 4 ¼ litre in 1936, substantially the same car with detail improvements in addition to the larger engine.
In 1938 the M-series or ‘overdrive’ cars were introduced, essentially a continuation of the 4 ¼ litre but with an overdrive top gear and a rear axle ratio designed to cope with the high-speed roads being built on the Continent.

Production numbers
Bentley 4 ¼ Litre 1936 - 1938 and M-Series 1938 - 1939
6 cylinders, capacity 4257cc. Separate cast iron block and two-piece 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
Coil ignition system with standby coil mounted together. Centrifugal advance with hand override.
Cooling system
Engine driven water pump and fan. Thermostatically controlled radiator shutters. 1938 in-line thermostat and radiator shutters fixed in open position.
Twin SU carburettors with hand operated choke, mounted on water-heated inlet manifold.
Fuel: : 18 gallon rear tank with double SU fuel pumps mounted on firewall. Electric gauge. Low fuel warning lamp.
4-speed gearbox in unit with engine. Synchromesh 3rd and top. 1938 direct drive 3rd gear, overdrive top. Right hand gearchange. Clutch, Borg and Beck type. Open drive propeller shaft.
Semi-elliptic leaf springs front and rear. Hydraulic shock dampers equipped with ‘Ride Control’.
Internal expanding 4 – wheel operation with independent handbrake on the rear wheels. Mechanical brake servo motor driven from the gearbox.
Worm and nut. 1938 Marles cam and roller steering box.
Chassis lubrication
Centralised ‘One-Shot’ lubrication system.