Speedway Workshop

Today in Motorcycle History

The DT Rudge (1930)

The 499cc dirt-track Rudge, designed by a firm which is renowned for its successful racing engines, has a very big following.

The power unit is a special four-valve Rudge type, and it has a bore and stroke of 85mm. X 88mm. It is tuned as standard to run on RDI, and at 5,500 r.p.m. develops about 35 b.h.p. A ribbed crankcase houses the flywheel assembly, which has 71/4-inch-diameter flywheels with the mainshafts running in ball and roller bearings. A two-ring aluminium-alloy slipper piston, with fully-floating 3/4-inch diameter gudgeon pin, is used, giving a compression ratio of about 10:I. The overhead valve gear incorporates enclosed roller-bearing rockers.


Python Four Valve Head

Rudge Python 250, 350 and 500cc engines were introduced in 1931. Borgo used 4V heads in 1920.

As on the Douglas, a wet-sump lubrication system is used, enabling the crankcase to be drained between races. It comprises an internal mechanical pump, with "tell-tale" plunger feeding oil to the rear of the cylinder, and a hand-operated pump supplying oil direct to the crankcase.

Fuel is supplied to the engine from a special Amal carburettor, with dual float chambers and quick-action twist-grip control. Two independent fuel feeds are led to the carburettor from the half-gallon tank. Two 11/2inc-diameter exhausts of the straight-through type carry away the products of combustion. Protection from
flying cinders is afforded by a large front shield situated in front of the M-L magneto. A magneto cut-out is provided as an extra.

The frame is of the successful type introduced in 1930, giving a ground clearance of 4 inches and a wheel base of 52 inches. A special frame designed to give spectacular sliding is available as an alternative.

The forks are of the new Webb speedway pattern, with steering damper. Mounted below the oil tank is a special Rudge countershaft gear box with a standard gear ratio of 7.7:1, giving a maximum speed of approximately 58 m.p.h. Variation of the gear ratio is obtained by changing the small countershaft sprocket, which normally has1=8 teeth. Alternative sprockets with 16, 17, 19 teeth give gear ratios of 8.7, 8.2 and 7.3:1 respectively. Fitted to the countershaft, which has roller bearings, is a clutch with " Ferodo " rings. Chain dimensions are 1/2x.305 inch and 5/8x.305 inch respectively. The fuel tank, which is enameled red, has a capacity of 1/2 a gallon, and has a special quickly operated filler cap.

The saddle is a narrow sorbo-topped Lycett.
A variation on this was of course the "Rudge-JAP" - as shown in the following picture* that was kindly sent to me by
Richard Snodin and shot at the 1999 BMF Rally.

* One or more images missing (×)

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