When a camshaft is located below the cylinder head, the rocker arms are activated by

• A. Direct acting lifters
• B. Hydraulic actuators
• C. Rocker arm shafts
• D. Push rods or tubes

Answer: (D)

When the camshaft sits below the cylinder head, the motion from the cam lobes has to be transmitted up to the valve train through an intermediate linkage. That role is filled by pushrods or tubes. The cam lobe pushes a lifter, which moves the pushrod upward; the pushrod then drives the rocker arm, causing it to pivot and open the valve against the valve spring. Hydraulic lifters may be present to take up lash, but they don’t replace the need for a pushrod in this configuration. Directly acting lifters wouldn’t fit this layout, and the pushrod/tube path is what allows the rocker arms to be activated when the cam is in the block.