Cam mechanisms

A cam mechanism for controlling the motion of cylinder head valve means of an internal combustion engine, the cam mechanism comprising:

• a camshaft having first and second cams which rotate therewith, the first having a cam profile which imparts a first lift and the second cam having a cam profile which imparts a second higher lift, and
• a drive mechanism operable to relay drive from the first or the second cam to the controlled cylinder head valve means, the drive mechanism comprising first and second cam follower means engageable respectively with the first and second cams and engagement means for engaging the first and second cam follower means with their respective cams, the cylinder head valve means further comprising first and second cylinder head valves,
• said drive mechanism having three operating conditions;
• (a) a first operating condition in which the first cam follower means is engaged with the first cam and the first cylinder head valve is driven by the first cam,
• (b) a second operating condition in which the second cam follower means is engaged with the second cam and the first and second cylinder head valves are both driven by the second cam;
• and
• (c) a third operating condition in which both the first and second cam follower means are disengaged from the first and second cams,
• wherein in the first operating condition, the first cylinder head valve receives a lift different from the lift received by the second cylinder head valve.