Rudge 4 valve, 4 speed
In the 1920s, overhead-valve engines pushed the side-valve out of racing – but one company took it a step further, producing four-valve engines that led the world by the end of the decade
Rudge Whitworth’s model development came in a series of innovative leaps, perhaps the most significant of which being their adoption of a four-valve cylinder head and four-speed gearbox at a time when most competitors were still making three-speed side-valves. The so-called ‘Rudge Four’ of 1924 replaced a model that had certainly served its time, dating right back to 1911.
Originating from the Coventry bicycle industry, Rudge had been relatively late in producing motorcycles, but their first production model proved durable enough to carry on for nearly a decade. The 500cc of 1911 featured their own ‘inlet-over-exhaust’ (or ‘F-head’) engine, with the exhaust valve side-mounted in the cylinder and the inlet vertically above it in the head. Although tending to look untidy, this system had its advantages and the Rudge soon gained a reputation for good performance – but what really made the Rudge successful was the invention of the ‘Multi’ gear.
Although the gearing of single-speed, belt-driven bikes could be altered by widening the front pulley flanges, this adjustment required tools and catered for rider weight or local terrain more than dropping down for a fast corner. Rudge’s ‘Multi’ system was like a manual version of a modern scooter’s automatic variable drive; one pulley widens and the other narrows, thus maintaining belt tension and giving a wider spread of ratios. This system kept the Multi effective through various models, including a 750cc big single and even a 998cc V-twin version, the ‘Multwin’. By the early 1920s however, the countershaft gearbox, still in use today, was becoming the transmission of choice – and it was growing obvious from the TT races that overheadvalve engines were going to take over from side-valves. In 1923, Rudge prototyped a new engine – and although it retained the same 85 x 88 dimensions, it was now overhead valve. Despite the performance advantage – 50% more power than the old F-head – overhead valve had its detractors. With the materials of the day, valve breakage was common and while it spelled disaster for an ohv engine it rarely damaged F-heads or side-valves. Also, the big valves in vogue at the time affected piston crown and combustion chamber design as well as weakening the head casting. Using four smaller valves would offer more flexibility; they
‘RACING SUCCESS FOLLOWED FOR THE FOUR-VALVE RUDGE’
could be made relatively stronger, were less likely to collide with the piston and were less invasive to the head structure. It wasn’t Rudge’s own idea – engine specialist Harry Ricardo had already produced a four-valve head for Triumph in 1921 – but Rudge were to make it their signature and ultimately to develop it through to a fully radial layout. The other feature of the new machine was Rudge’s own countershaft gearbox; possibly as a nod to the days of the old Multi, Rudge supplied four speeds where most manufacturers offered just three. This ’box was efficient enough that it remained in production with only minor refinements up until the end of Rudge production in 1939.
The Rudge Four, with its ‘Four Valves-four Speeds’ tank legend was released in 1924. Considered too powerful for the existing Multi chassis, production initially concentrated on a 350cc version until the chassis could be brought up to cope with the five hundred. The 350 was dropped for 1926 and Rudge offered the four-valve 500 in Economy, Touring and Sports guises – the Sports model putting out 18bhp, enough for 80mph on a good day.
Another feature of the Four was linked brakes – front and rear operated together by the foot pedal, with the usual handlebar lever for front brake only. Linked braking was an idea from the car world – compete with an ‘all wheel braking’ warning triangle. It didn’t catch on in motorcycles, but Rudge persevered with it until the end. The brakes themselves were rim type – fibre blocks brought to bear on the outside of large-diameter flat brake rims, they were a little like a disc brake with only one pad and about as effective, but this was addressed for 1928. Rudge leapt forward again, fitting eight-inch diameter drum brakes front and rear at a time when five or six was more usual.
This and a frame redesign with a saddle tank replacing the old flat tank design brought the four-valve Rudge up to date and competition successes followed. Speedway arrived in Britain in 1928 and for a time Rudge dominated the sport. Trials and racing successes mounted and at the end of the year Graham Walker won the Ulster Grand Prix at the world record race speed of 80mph. That achievement led to Rudge’s few years of success and the famous ‘Ulster’ model – but unfortunately, far across the Atlantic, economic problems that would plunge nations into despair were already beginning to mount...
The four-valve Rudge Four wasn’t the best bike of the 1920s, but it proved a successful host for innovations that we take for granted today. It’s a shame that their reward was to find fame at a time when few had money to spend – a blow from which the company never recovered.