Cam ramps Camshaft Cam track Cam lobe Roller Cam ring Cam roller Pressure oil Case Tappet Adjusting screw Rocker arm Return oil Lock screw Push rod tube Tappet guide Seat Port Valve guide Valve spring Figure 1-24. Valve-operating mechanism (radial engine).  Figure 1-23. Typical cam lobes. the cam lobe to permit the rocker arm to be eased into contact  with the valve tip and thus reduce the shock load which would  otherwise occur. The valve operating mechanism consists of a  cam ring or camshaft equipped with lobes that work against a  cam roller or a cam follower.  [Figures 1-24  and  1-25]  The cam  follower pushes a push rod and ball socket, actuating a rocker  arm, which in turn opens the valve. Springs, which slip over  the stem of the valves and are held in place by the valve-spring  retaining washer and stem key, close each valve and push the  valve mechanism in the opposite direction.  [Figure 1-26] The valve mechanism of a radial engine is operated by one or  two cam rings, depending upon the number of rows of cylinders.  In a single-row radial engine, one ring with a double cam  track is used. One track operates the intake valves, the other  operates the exhaust valves. The cam ring is a circular piece of  steel with a series of cams or lobes on the outer surface. The  surface of these lobes and the space between them (on which  the cam rollers ride) is known as the cam track. As the cam ring  revolves, the lobes cause the cam roller to raise the tappet in the  tappet guide, thereby transmitting the force through the push  rod and rocker arm to open the valve. In a single-row radial  engine, the cam ring is usually located between the propeller  reduction gearing and the front end of the power section. In a  twin-row radial engine, a second cam for the operation of the  valves in the rear row is installed between the rear end of the  power section and the supercharger section. periphery, one set (cam track) for the intake valves and the  other for the exhaust valves. The cam rings used may have  four or five lobes on both the intake and the exhaust tracks.  The timing of the valve events is determined by the spacing  of these lobes and the speed and direction at which the cam  rings are driven in relation to the speed and direction of the  crankshaft. The method of driving the cam varies on different  makes of engines. The cam ring can be designed with teeth  on either the inside or outside periphery. If the reduction  gear meshes with the teeth on the outside of the ring, the  cam turns in the direction of rotation of the crankshaft. If the  ring is driven from the inside, the cam turns in the opposite  direction from the crankshaft.  [Figure 1-24] The cam ring is mounted concentrically with the crankshaft  and is driven by the crankshaft at a reduced rate of speed  through the cam intermediate drive gear assembly. The cam  ring has two parallel sets of lobes spaced around the outer  Cam Rings 1-19