Today in Motorcycle History

JD Motorcycles for 1923

JD 116cc Twostroke Engine for 1923

Miniature intended to appeal to those who do not wish to forsake the pedal cycle entirely - the 116 c.c. two-stroke J.D.

The 1922 Olympia Show.

J.D. (Stand 74.)

Super Motorised Bicycle.

1¼ H.P. Model.

51x57 mm. (116 c.c); single cyl. two-stroke; petroil lubrication; Vici carburetter; chain-driven mag.; single-speed: clutch, no kick-starter: chain-cum-friction drive; 26x1¾in. tyres. Price: Solo, £35.

Bowden Wire, Ltd., Willesden Junction, N.W.10.

Although the J.D. machine is essentially a motor-assisted bicycle, nevertheless it is designed as a whole, not as an attachment to be fitted to ah ordinary bicycle strengthened for the purpose. The engine is particularly well made, the manufacturers assuming that with so small a cubic capacity the power unit would be doing high duty for the greater part of its time, and, therefore, needs to be made better than would be the case with a larger engine.

Power is transmitted from the crankshaft to reduction gearing, and thence to a pulley composed of special friction material engaging with what appears at first sight to be a belt pulley attached to the rear wheel spokes. This pulley can be disengaged by a control on the handle-bar when a clutch action is desired, and is held in position by coil spring mechanism acting through a bell crank lever in such a manner that irregularities in the driven rim have no effect upon the drive.

Those who desire to test the efficiency of the friction drive and understand its operation should inspect the working models on the stand driven by electric motors.

Olympia Show 1922
The Motor Cycle, November 30th, 1922. Page 864

JD Two-stroke Engine 1922

Power unit complete, illustrating the, comparatively huge silencer.
R. Crankshaft, connecting rod and piston assembled, illustrating how the latter two members may be removed without dismantling the crank case.

JD Transmission 1922

Friction transmission is used which by the Bowden mechanism shown provides a clutch and free engine. Contact pressure is gained chiefly by the pull of the driving chain tending to jamb the small friction disc against the flange on the wheel.


Strongly-built 116 c.c. Miniature Produced by Bowden Wire, Ltd. Novel Friction Transmission.

AT a first glance at the J.D. motor cycle (a new product of Bowden Wire, Ltd.), one is inclined to say, "Ah, another motorised bicycle!" But one very soon alters that opinion; and the more the design is studied the more it is admired.

An attempt has been made to do something that has never been done before, i.e., to evolve a self-propelled vehicle that will, by reason of its similarity to an ordinary bicycle and its simplicity, attract the pedal cyclist, but to design and build it with the same care and thoroughness as are bestowed on the most expensive machines of to-day. For this reason it is not cheap, in any sense of the word. It has not been built down to a price; "everything of the best" was the producer's motto, and it was then estimated that the cost would be £40.

Only Superficially Like a Pedal Cycle.

The resemblance to a motor-assisted pedal cycle is merely superficial. The frame, which has a sloping top tube, is amply strong enough for the roughest use in the hands of the novice; double-butted tubes are used where possible. After considerable experiment spring forks were discarded as unnecessary, a rigid girder type being fitted.

Orthodox three-port design is followed in the 116 c.c. (51x57 mm.) two-stroke engine, which, however, is notable for the excellence of its finish and the fine limits to which its component parts are made. Instead of being in front, the transfer port is at the side of the cylinder, the deflector thus being at right angles to the gudgeon pin. The crankshaft is supported at the flywheel side only -- on double row roller bearings -- and this construction permits the removal of piston and connecting rod complete by simply sliding them off at the big end, of course after the cylinder and crank case cover plate have been removed -- the latter to allow sufficient clearance. Accessibility is a feature generally.

A very large silencer is fitted, this, like the other aluminium portions of the machine, being a die casting.

Magneto and transmission sprockets, together, are bolted on to a spigot on the inner side of the outside flywheel, which itself is keyed on to a taper on the main shaft.

Simple and Effective Friction Drive.

Friction transmission is employed. Carried on a bracket pivoted on the rear stays is a sprocket, driven by the engine, and a U-shaped disc of a special friction material, which makes contact with the inside of a U section flange bolted to the rear wheel. To de-clutch, the driving disc is simply swung clear by a Bowden lever on the handle-bar acting against two fairly light coil springs. Sufficient pressure to gain a non-slip contact in all weathers is gained chiefly .from the tendency of the driving member, helped by the pull of the driving chain, to jamb forwards. In practice this works admirably. The gear ratio is between 9 and 10 to 1. The system has the additional advantage that in free engine (held out by the usual handle-bar ratchet clip) no friction is caused by any transmission members revolving; coasting is thus as free as on a pedal cycle. The detail design, and workmanship, as in the power unit, are very fine.

Endless chains are used for the magneto and transmission, adjustment being gained by sliding the whole engine unit up the front tube. To accommodate this movement the rear engine lug embodies a swinging link.

Pedalling gear is fitted, the chain adjustment in this case being in the eccentric bottom bracket, thus leaving the transmission centres undisturbed.

Equipment and Controls.

An aluminium guard protects the driving and magneto chains, and fairly wide and amply strong mudguards with number-plates are standard. The equipment throughout is of the first quality, down to a Lucas Girder spanner in the tool kit.

There are only five control levers -- front and rear brake (the latter of neat but most effective design working in the transmission rim), throttle of single lever carburetter, "clutch " (or free engine), and decompressor. "Petroil" lubrication and fixed ignition all tend towards simplicity.

The tank holds six pints of fuel, sufficient for 100 miles or so. All on, the machine weighs about 80 lbs., but the designers wish it to be made clear that no attempt has been made to obtain a low figure here. Rather, the weight figure simply "happened."

Extended road tests for three years have failed to find any weak spots, and the road performance without pedal assistance is remarkably good.

It will be most interesting to see how the public receives this miniature, for it will readily be admitted that the policy which inspired it is a most courageous one, in these days of price reduction.
The Motor Cycle, September 28th, 1922. Page 435

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