The single-cylinder 350 cc (21 cu in) Rudge Four, named for having four speeds and four valves, showed markedly superior performance to the competition on release, having more power than its 500 cc (31 cu in) predecessor.
Rudge engineer George Hack is said to have taken his design idea from the four-valve Triumph Ricardo (produced from 1921–28).
He designed a four-valve head for Rudge and in 1924 they produced their first four-valve cylinder head on a 350 cc engine.
The valves were arranged in parallel, and were not radial.

In 1925, a 500 cc version with linked front and rear brakes appeared, and the big end bearings were now fed oil through the crankshaft pin.
The old 350 cc was dropped in 1926.
For 1928 Rudge motorcycles were fitted with saddle tanks, and 8-inch internal expanding drum brakes.
Stanley Glanfield designed a Rudge for dirt racing, marketed from 1928 as the Glanfield Rudge.
The single-cylinder 350 cc (21 cu in) Rudge Four, named for having four speeds and four valves, showed markedly superior performance to the competition on release, having more power than its 500 cc (31 cu in) predecessor. Rudge engineer George Hack is said to have taken his design idea from the four-valve Triumph Ricardo (produced from 1921–28). He designed a four-valve head for Rudge and in 1924 they produced their first four-valve cylinder head on a 350 cc engine. The valves were arranged in parallel, and were not radial.
In 1925, a 500 cc version with linked front and rear brakes appeared, and the big end bearings were now fed oil through the crankshaft pin. The old 350 cc was dropped in 1926. For 1928 Rudge motorcycles were fitted with saddle tanks, and 8-inch internal expanding drum brakes. Stanley Glanfield designed a Rudge for dirt racing, marketed from 1928 as the Glanfield Rudge.
Rudge-Whitworth