The valve train is an engine part which experiences severe lubrication and special effort is required to lubricate it effectively. We have investigated the role of oil composition with respect to the friction properties of a cam/tappet contact using a specially designed instrument. This tribometer determines friction during cam revolution by analysing time-dependent cam-shafttorque measurements.
The friction coefficient depends on the position of the cam relative to the tappet, as predicted by the kinematics of the system. Boundary lubrication is predominant in positions close to top lift, whereas milder lubrication conditions occur at small lift. Data on some pure mineral oils and friction-modified oils are presented.