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British Motorcycles

Lea-Francis Models for 1914-1915

A Lea-Francis Three-speed Gear.

NEW FITTING FOR 1915, INCORPORATED IN ORIGINAL GEAR BOX.

THE 1915 model of the Lea-Francis will be equipped with a three-speed gear. Ever since their first public appearance the Lea-Francis machines have attracted a large amount of attention, not only on account of their line performances in reliability trials, but also because of their excellence in general design, and particularly detail work. Up to date, the modifications which have been carried out have been comparatively unimportant, but we are now able to describe and illustrate the latest type of gear giving three ratios, which will be a standard fitting in the near future. The gear has been thoroughly tested on the road, and has been proved to be perfectly satisfactory after prolonged trials, so that it is not by any means a new device to be tried at the expense of the public.

Outwardly, the appearance is but little altered, for the new gear is contained in the same shell as before, and is mounted in the same type of bottom bracket lug. The control is, of course, somewhat different, and though the lever and quadrant are on the usual L.F. lines, with an extra notch for the additional ratio, the selecting mechanism is somewhat unusual. Attached to the lower tank tube close to the seat post is a fixed bracket with two extension pieces, which pass through a sliding cam plate, the movement of which is controlled by the change speed lever. The plate slides in a straight line, horizontally only, and is formed with two specially shaped cam slots, into each of which a roller projects from the two vertical, striking rods. These rods are held in position by a plate fixed to the stationary bracket, and formed with a groove for each control rod. In this manner the horizontal movement of the cam plates transmits vertical motion only to the control rods, as can be seen from the appended sketch. The whole selector mechanism is well out of the way of grit and mud, and is as fool- proof as possible.

Gears Always in Mesh.

There are three sets of dog clutches in the gear box - two on the main shaft and one on the layshaft, and the gears are always in mesh. Thus every change is made by means of dog clutches, and, consequently, a very much finer pitch can be used. In point of fact, 16 pitch teeth are employed throughout, which renders the drive very quiet.

The main driving shaft is splined, and extends right through the box, driving only the centre wheel. When this central wheel is moved to the left (away from the clutch) top gear is engaged, and a similar movement to the right brings the lower ratio into action. Middle is obtained by centralising the main shaft dogs and engaging the pair on the layshaft. The layshaft is a steel pin fixed in the gearbox on which the driven wheels revolve carrying with them two phosphor bronze bushes.

Besides the alterations to the gear, the clutch has been modified, with beneficial results. In the latest type the sprocket member is gripped between two material faced plates, and it is found that the new clutch will stand indefinite slipping, and yet grip firmly when home.

We have tried this gear on the road and it behaved just as one would expect any L.F. production to do. It changed easily up or down, the gears were silent and the speed and general comfort of the machine on the high gear were most pronounced.

Engine vibration on the top gear of 4.75 to 1 is practically nonexistent. Quite a good speed can be attained on the middle gear of 6.9 to 1, whilst the 12.3 to 1 low gear ensures an ascent of any rideable hill, and, moreover, renders the 1915 L.F. a very attractive proposition for sidecar work.

An account of the performance of this new gear on severe hills included in the A.C.U. Six Days Trials will be found in another article in this issue.

The Motor Cycle, October 29th, 1914. p484.



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