Thursday 23 July 2020

The Cambox

On the Velocette engine, the camshaft is driven by a bevel gear and lubrication of the bearings, cam and tappets is by oil that enters the cam chamber from the bevel drive housing by being pressure fed through a slot in the camshaft that aligns once per revolution with a slot in the phosphor-bronze bush that supports the shaft.

The arrangement here is entirely different; the camshaft is chain driven and there is no pressurisation inside the timing case to force oil into the cambox. An external oil supply must therefore be provided to lubricate the contact surfaces.

The design of the Velocette engine bevel drive provides plenty of opportunity to fit a good size bearing at the driven end of the camshaft. The loads are wholly radial and a large deep groove ball bearing was therefore fitted into a new bearing housing. A new shaft was made to support a new K17/2 cam, shown below.

 And the camshaft was completed by making a Vernier adjuster so that the valve timing could be easily set.

Finally, the cambox was drilled and tapped to accept a new oil feed that would be pressure fed directly from the pump. The picture below shows the new oil feed and also a restrictor that was plumbed into the system to control the amount of oil reaching the cambox. 

Oil that “escapes” from the cam chamber into the surrounding gutters is collected, shown below, and drained back into the engine, which is standard Velocette practice. Also, as per Velocette practice, oil that reaches the gutter on the inlet side is fed into the inlet valve guide. The 1/8" OD copper pipe for this oil feed can just be seen on the right of the picture.

Unfortunately, the cambox lubrication proved problematical during the shakedown of the bike and more will be said of this later.

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