4 – VALVE TRAIN
69
Piston Engine Fundamentals
TC010-05-01S
PUSHRODS (OHV)
In an OHV engine, pushrods transfer the lifting motion from the camshaft
and lifters to the valves. Pushrods are made of stiff steel tubing, with cups
or balls on the ends to mate with the lifters and rocker arms.
The pushrods flex slightly in normal operation, and this flexing is taken into
account when the cam lift is designed. On some engines, pushrods come
in varying lengths to provide an initial clearance adjustment with hydraulic
lifters.
ROCKER ARMS
The rocker arm reverses the direction of lift from the pushrod or camshaft
to the valve. Mazda engines use shaft-pivoted rocker arms, as shown in
Figure 50. The rocker arm is made of aluminum, and a pivot is drilled out
so the rocker arm can run on a hollow rocker arm shaft.
FIGURE 50.
Rocker arms are
fitted to shafts.
Rocker arm
shaft
Shaft-pivote
d rocker arm
Valve
Pushrod