Photo ou archives : F-M. Dumas
500 Grass-Track - 1937
Speed on grass
In Great Britain, during the years before and after WWII, grass-track racing was one of the most popular forms of motorcycle sports. It was run over circuits of varying length that Â– unlike Speedway Â– had both right- and left-hand bends and could be traced out in any field where permission could be obtained, often incorporating steep ascents and descents. Brands Hatch, a Grand Prix circuit, started as a grass track in the 1930s.
Many British makers built special grass-track machines. This OK-Supreme has a "five-stud" JAP 500 Speedway engine, so-called from the five studs retaining the cylinder head instead of the usual four. Since the high-compression Speedway units, running on methanol, had the tiresome habit of shedding their heads and grass-track circuits were longer than those used for Speedway, a gearbox was a useful addition.
Ernie Humphries, who was a partner in the OK company, resigned in 1926 and moved into a new factory to build a new motorcycle -the "OK-Supreme." Alec Bennett designed a squish-type head for the works JAP-engined racers for the 1928 Lightweight TT, won by Frank Longman's OK-Supreme after Bennett retired. Though OK-Supreme built its own engines after 1930, it continued to use JAP power units and specialized in grass-track racers. In 1946, Humphries' son John built some promising 346cc OK-Supreme-JAP grass-track bikes. But John was killed in a fall from a hotel window, and his 90-year-old father could not carry on production.
Engine: 497cc (80x99mm) air-cooled single-cylinder four-stroke; total-loss lubrication
Power Rating: 42 hp @ 6,000 rpm
Fuel System: Amal carburetor
Transmission: 4-speed, chain final drive
Suspension: girder forks (front); rigid (rear)
Brakes: drum (front & rear)
Wheels: 3.00x21 inch (front); 3.50x19 inch (rear)
Weight: 298 lb
Maximum Speed: 90 mph
OK-Supremes lived up to their name in both grass-track
and speedway racing, ridden by Fred Hudson, Andy Mackay and John Humphries.