Martinsyde Motorcycles

Martinsyde 500cc V-Twin 1921


Martinsyde 1921 500cc V-Twin

The 3 ½ h.p. Sports Martinsyde. The performance of this new model in the A.C.U. Six Days Trials was watched with interest.


Martinsyde 1921 500cc V-Twin

Chain cover of the 3 ½ h.p. Sports Martinsyde, showing the inspection cap by means of which the clutch spring adjuster is reached.


Martinsyde 1921 500cc V-Twin

A hinged magneto shield is fitted Note the spring impinging against the exterior of the magnets holding the cover in place.


The 3 ½ h.p. Martinsyde Sports Model - a Machine for High-speed Touring or Competition Work.

THE first appearance of the 3 ½ h.p. twin Martinsyde was at the end of last year when it was shown at the Olympia Show by Martinsyde, Ltd., of Maybury Hill, Woking; the machine has undergone considerable alteration and improvement since that date, and it reappeared in an improved form when it competed in the 500 miles race in the able hands of H, H, Bowen. Three of these machines have also been through the Six Days Trials their first appearance in a long reliability trial.

Some Distinctive Features.

The chief alteration lies in the shape of the frame, which is of symmetrical appearance with a sloping top tube, which latter is brought into line with the back forks. The main Martinsyde features are retained, such as additional stays between the top of the saddle tube and the bottom bracket supporting the gear box; while the engine, which has a bore and stroke of 60x88 mm. respectively (498 cc), is a small replica of the larger type utilised in the Martinsyde sidecar outfit, and possesses the well-known features of the overhead exhaust valves, made of stainless steel, with inlet valves below them. Best and Lloyd semi-automatic lubricator, ball bearing crank and camshafts, while roller, bearings are still retained for the big ends.

The front chain is protected by means of a chain cover, in the centre of which is a screw cap, which, when removed, allows access to the clutch spring, so that the latter may be easily adjusted. A light guard protects the top run of the rear chain. Footrests are fitted instead of footboards, and, in connection with this fact, it is worthy of note that the pedal actuating the rear brake lies midway between the front and rear offside footrests, so that it may equally well be applied by the toe when the foot is on the rear footrest as by the heel when the foot is on the front footrest.

Clip-on Magneto Shield.

Points of convenience have been carefully studied in this machine, and it is interesting to remark that the magneto is protected by a shield kept in position by a light spring, so that it can be swung forward at any time in order that the magneto may be inspected. The three-speed A.J.S. type gear box, though it incorporates a clutch, is not provided with a kick-starter. Particular note should be made of the large toolbags, which extend the whole length of the carrier, and are adequately protected by a metal casing. The oval section tank is secured by straps fastened on to lugs on the secondary tube, and holds one and a half gallons of petrol and three pints of oil.

The top gear is 4 ½ to 1, and the equipment includes two-lever Amac carburetter, Dunlop 650x65 mm. tyres, and Brooks saddle. The weight is given as under 300 lb.

The MotorCycle September 8th, 1921.

Source: The Motor Cycle

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