The valve mechanism of an opposed engine is operated by a camshaft. The camshaft is driven by a gear that mates with another gear attached to the crankshaft. The camshaft Usually rotates at one-half the crankshaft speed. in other words, when the cam shaft rotates two cycles the cam shaft only complete one cycle.There are number of lobes which are machined on the cam shaft and As the camshaft revolves, the lobes cause the tappet assembly to rise in the tappet guide, transmitting the force through the push rod and rocker arm to open the valve according to the sequence .
The profile of the lobe controls in terms of crankshaft degrees the point of valve opening, the rate of valve opening, the period the valve remains open, the rate of valve closing and the point at which the valve closes.
For radial engine the cam shaft operation is provided by a ring which is known as the Cam Ring. this is a circular metal ring with the lobes on it in a circler. this helps the radial engine rocker arms to be opened and closed as per the firing order. More information on radial engine cam ring will posted in next post.