Phantom 2 camshaft and followers

Phantom 2 camshaft and followers

History of Phantom 2 camshaft design

The Phantom 2 was the first pre-war Rolls-Royce engine from the Silver Ghost onwards that had a cam follower or tappet that was in sliding contact with the camshaft. All earlier engines had a follower equipped with a roller in contact with the cam lobe, which resulted in minimal wear on the cam. However the life of both the Phantom 2 cam and the followers has for long been a source of concern.

Because the contact face of the follower presented to the cam is convex the contact point between the two surfaces will move across the face of the follower, This spreads the wear of the follower, but not enough to reduce the wear on the follower. The follower was made from a case-hardened steel, having a hardened face for longevity. Variations on this involved either depositing a layer of Stellite on the face, or protecting the face with a layer of hard chrome to extend the life of the follower, with varying degrees of success.

Other changes were made to the cam shaft and cam follower arrangement during the course of the Phantom 2 production. The spring which keeps the follower in contact with the cam lobe was uprated to increase the pressure between the follower and lobe by a factor of 4. This was introduced at chassis 2MY. The reason for the change in spring is unknown, but it may be that engines were being driven harder and faster, particularly with the introduction of the high compression cylinder head. This could result in the cam follower being ‘thrown’ off the lobe at very high speeds

The uprated cam follower spring was followed by the introduction of a high-lift cam at chassis 102MY.

The fitting of the high-lift cam, together with the uprated spring, reduced the life of the camshaft or followers significantly, and it was withdrawn at chassis 101TA when the earlier camshaft was reintroduced. The stronger spring was retained.

Cam follower lubrication

Crucial to the life of the cam shaft and cam follower is the lubrication of the contact point between the two. This can be improved relatively simply.

The rotation of the camshaft exerts a sideways force on the cam follower, pushing it to the off-side (right side, when viewed from the rear of the car) of the engine. Oil flowing down the gap between the near-side of the follower and the guide will be picked up by the rotation of the cam and swept into the contact area between the follower and the lobe. However the amount of oil available is limited by the clearance between the follower and guide, and by the supply of oil running down the follower from above.

The life of the cam follower can be extended if the lubrication to the contact point between the lobe and follower is improved. In order to enhance the oil flow we have made a small modification to the cam follower by introducing a vertical groove in the side face of the cam follower foot. With the follower fitted with this groove on the near-side of the engine (or left side when viewed from the rear of the car) extra oil is able to drain from above the head of the follower onto the lobe and is drawn into the contact point. To ensure a good supply of oil at this point the aluminium sleeve that is fitted around the follower stem and return spring is modified by blanking off the drain slots at the bottom of the sleeve, allowing the oil to collect above the follower head rather than drain away into the sump.

Our recommendation

Few owners today are likely to drive their Phantom 2 so hard that the cam follower will lift away from the cam lobe. Therefore to extend the life of the camshaft and followers, without embarking on a roller follower conversion, our recommendation is as follows:
1 Use a normal camshaft (not high lift).
2 Fit followers with an oil drain groove in one face. Our part number GHD100M.
3 Fit modified aluminium spacer sleeves. Our part number GHD081.
4 Use the earlier cam follower spring, part number GHD040.

With acknowledgement to John Reynolds of Bradley Engineering for his advice on this issue.