The 1907 lightweight motorcycle

The 1907 lightweight FN motorcycle

The first FN motorcycles were lightweight single-cylinder machines with belt drive. But with the advent of the four-cylinder shaft-drive model in 1905, these early singles with their high frames were beginning to look very dated. For 1907, a new single-cylinder machine was introduced, with a frame design inspired by the four-cylinder. I have a motor from one of these machines, which sports a rather interesting internally-geared pulley.

1907 lightweight FN motor

From a period catalogue, we find the following specifications for the model:

ENGINE	1 3/4 h.p. with transparent port to examine lubrication, exhaust valve operated from handle bar. Internally geared F.N. Patent Engine Pulley.
CARBURETTER	F.N. Auxiliary Air and Throttle operated from levers on top of tank.
IGNITION	Simms-Bosch High Tension Magneto, driven by spur gears enclosed in case.
FRAME	20 in. Weldless Steel tubing, all lugs, joints, brackets, &c., are drop-steel forgings.
TANK	Sheet brass, oxidised: capacity 1 gallon (130 miles). Separate tank for lubricating oil, capacity 3 pints
FORKS	Very effective Suspension Forks, giving great comfort to the motorist
MUDGUARDS	Extending over front wheel, rear mudguard being very easily dismounted by pushing forward, a great convenience in case of puncture.
WHEELS	26 in. drop-forged steel hubs and spindles. Tyres 2 in.
FITTINGS	Large, strong toolbag, with complete outfit of tools, together with accessories, such as spark plug, belt fastener, petrol strainer, &c.

Removing the large nut, and another (left hand thread) one underneath allows the pulley to be removed and the internal gearing revealed. The ratio is around 3 1/2:1. Just how the belt-tensionner is attached to the tankside lever I'm not sure: it seems to be a rack-and-pinion affair. Can anyone fill me in? (Thanks Jacques - see below.)

Internally-geared pulley on the 1907 FN

The lightweight model had only a brief life, replaced in 1909 by the shaft-drive single which was to last into the early 1920's. I have no idea how many of the lightweights were produced, but there is quite a bit of surviving junk from them in Australia. In addition to a complete bike which exists in Western Australia, I have seen three motors in recent years (one of which can be seen in the FN Photo Gallery), and a frame which has sadly been taken to with a hacksaw.

Thanks to Jacques Maertens for the following photo of a lightweight under restoration in Belgium. Looking at the photo, we see that the "rack" to adjust the belt tension is driven by a worm gear. Just twirl the lever if the belt begins to slip!

1907 FN in Belgium

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