Philipson Pulley

Sadly it is not just veteran machines that are getting older. So are their riders. The value of single-speed fixed drivers has tended to stay more-or-less static in recent years because many of the people interested in them are finding them increasingly strenuous to ride. This situation is likely to get worse. The value of a single speed veteran fitted with a period, authentic-looking, variable speed gear that overcomes these problems should result in an increased value, which is estimated to be about double the cost of the pulley.

Philipson Pulley

a. Pulley outer face
b. Pulley inner face
c. Key
d. Spring Box
. Clock Spring
g. Sleeve
g'. Bolt-spring to sleeve
k. End Cover
n'. Nut

The Philipson Pulley was introduced in 1911 and remained on sale until 1924, by which time it's market, the single-speed belt driver, had finally disappeared. It gained immediate acclaim and was by far the most successful of the many proprietary variable gears placed on the market to make single-speed belt drivers more tractable. It was often retrofitted to older machined. Philipson pulleys were widely used in the TT and other sporting events.

WHAT IS IT?
A variable pulley that automatically adjusts the gear ratio, depending on the load on the engine.

HOW DOES IT WORK?
The belt-pulley faces are held together by a large clock spring. When a hill is encountered, the extra engine torque put out in climbing the hill overcomes the spring and the pulley faces move apart. The belt then moves down to a smaller diameter of the pulley i.e. the gear ratio is lowered. When the top of the hill is reached, the engine torque is reduced and the spring is able to close the pulley and restore the original (higher) gear ratio.

WHAT ABOUT STARTING THE ENGINE?
At rest the engine is not supplying any torque and the pulley faces are held together by the spring. The bike therefore remains on high gear while you pedal on the stand to start the engine. You do not have to pedal furiously in a low gear to start the engine.

CAN IT BE USED FOR SLOW RIDING?
Yes. To select a low gear for riding in traffic it is only necessary to put your foot on the brass spring box to slow its rotation. This will automatically open the pulley. When you remove your foot the pulley will automatically reset itself to the higher ratio. Some veteran riders used to rig up a hand lever and a break pad for the same purpose.

HOW EASY IS IT TO INSTALL?
Very easy, takes about 20 minutes. The old engine pulley is removed. The new pulley is lightly lapped on with valve grinding paste to "fit" the taper. The Philipson is then secured in place with the original nut.

 

It is usually necessary to put a slight "set" in the pedal crank to clear the pulley. The belt is adjusted, and you are ready to ride! NOTE HOWEVER: The spring box contains a powerful spring that could cause injury if you attempt to dismantle this component.

HOW GOOD A REPLICA IS IT?
Visually identical to real thing, including the Edwardian Script on the cover, but most components are made of higher quality materials than were available in 1911.

CAN IT BE USED AS A CLUTCH?
Philipson used to advise against this due to excessive belt wear.

DO YOU NEED A SEPARATE BELT-TENSIONER?
No, because a belt in good condition will always grip across it's top surface onto both the pulley flanges. After all, it is the wedging action of the belt that forces the pulley faces apart.