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An interesting collection of Dirt Track machines, from the estate of the late Sid King, are coming up for auction at Cheffin's sale of October 18th. Sidney King worked for Victor Martin (who made speedway racing chassis) in 1949/50, and picked up a passion for dirt track machines. He also restored many Brooklands racers.
This collection makes a neat 'vertical flight', showing the evolution of the Dirt Track racing motorcycle, from the early days of Douglas dominance, through the Rudge days, to the JAP era. After Dirt Track racing was introduced in England in 1927, most manufacturers developed (or at least offered) a 'DT' machine - Scott, Velocette, Norton, Sunbeam, Panther(!), Rudge, etc. Some of these were successful, some not, but all are rare at this point, and are an interesting niche for collectors.
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This 1928 Douglas DT5 is exactly the type used by all comers in the 1920's, as it was simply the best available at the dawn of the Speedway era in England. The DT Douggie has a unique frame, long and low, and is a hybrid of their TT and RA racing models. The Douglas engine was dominant on the road race and track circuit as well during the mid 20's, being the first British motorcycle timed at 100mph in '22 (Cyril Pullin at Brooklands), and winning the Isle of Man Senior TT in 1923 and the Sidecar TT in '23 and '25. It was natural that the Aussies would find one of the fastest machines on the market to be the best dirt racer (or 'dracer' as some said).
A second DT Douglas is avaialble in 'kit form' with two engines (which I've heard is a good idea for a racing Douglas...'if you're going to ride it hard, better have a spare engine...' was the quote from one who tunes and sprints them in England).
This 1930 Rudge (fetching in red) was the machine which supplanted the Douglas on the track, as it was more compact, and developed a bit more reliable power, Rudge having by 1929 really come into their own. The four-valve 500cc engine was also dominant on the road race tracks in this period, winning the 1930 Junior and Senior Isle of Man TTs, as well as the 1928 Ulster GP.
As happens in racing, Rudge itself was supplanted, in what was by then called 'Speedway', by J.A.P.-engined specials (J.A.P. supplied only engines, not whole motorcycles), which held sway until the 1960's. This Martin-JAP is an example of the myriad specialty frames available to a Speedway racer, many of which saw success on the tracks of England and the Commonwealth. Sid King worked for Victor Martin Ltd (Vic being a former JAP employee), who contracted with JAP to sell their engines. Martins basically copied the Rudge frame to house the JAP five-stud speedway engine.
Another JAP motivated machine is this Comerford-JAP Special, which was originally designed by George Wallis for the Surrey motorcycle dealer Comerfords. The original Wallis, from 1929, used a Blackburne engine; the frame is based on the Harley 'Peashooter' (Wallis had been competition manager for H-D in Britain), and the total package weighed 185lbs. There are a few significant departures between these two 1935 machines - the Wallis machine has forks similar to an early Scott, with a short telescopic tube near the axle (originally using Andre dampers as well), while the Martin has more typical short girder forks, which are still the standard today.
When JAP introduced their own 'Dirt Track' engine in 1930, the Wallis became suddenly an unbeatable machine in the hands of Wal Phillips. It sold through Comerfords originally for £35 as a rollling chassis, or £75 complete with engine. [More on the Wallis can be found in the July 1986 Classic Motorcycle]The JAP speedway engine is a specialized tool, with simple and robust construction, necessary for the very high compression ratios used with alcohol fuel (14 thru 16:1), and flat-out use for short races. The lubrication is total-loss, metered by a Pilgrim pump in the timing chest, and the crankcase is heavily finned for strength. Cooling is not an issue with alcohol fuel, as it burns very cool, so the finning on these engines is scant. They have a surprisingly long stroke for a racing engine (80x99mm), but the ability to pull away quickly is essential in Speedway, so the power band must begin in the lower rev range. Because of their minimal finning, very few of these DT JAP engines made their way into road racers, but some hillclimbers found them ideal for a short blast up a drive, and this is perhaps where they are best seen in action today.