LO 9-5 Identify and describe the purpose, construction, and operation of components used in the valve train

LO 9-05: Identify and describe the purpose, construction, and operation of components used in the valve train.

Pushrods

Pushrods transmit the cam actuation force from the followers to the rocker levers. To reduce weight and inertia at high speeds, longer pushrods are usually hollow. When servicing, the pushrods should be checked for wear at each end as well as bending caused by miss-adjustment or high-speed valve float. Some pushrods will use a hardened end at the rocker lever to withstand greater friction at this point. If the weld at the ball socket end fractures, oil can enter and accumulate inside the pushrod. The easiest way to check for oil entering the pushrod is to listen to the sound made when the pushrod is dropped. A pushrod filled with oil will make a distinctively different thud-like sound when it is dropped and will not bounce as much as a good pushrod. Shorter, solid pushrods capable of transmitting larger forces with less flexing are also commonly used with high-mounted camshafts Figure 45. Solid, short pushrods allow for higher injection pressures and reduced injection lag.

FIGURE 09-45: A high-mounted camshaft is located as close to the cylinder head as possible to shorten the length, inertia, and weight of the pushrods. Solid, short pushrods will not flex easily.

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