Question 8 MODE02 - Assistant MODU Engineer

The Correct Answer is A **Explanation for Option A (Correct):** The primary function of a push rod is to transmit the linear motion generated by the camshaft and tappet (or lifter) to the rocker arm assembly located above, typically in the cylinder head. If the camshaft is located some distance below the valve gear (e.g., in the engine block), a mechanical linkage is required to bridge this distance. The push rod serves as this linkage, making its use necessary in engines with this specific configuration (often referred to as overhead valve or OHV engines). **Explanation of Incorrect Options:** * **B) the rocker arms are pivoted near their centers:** The pivot point of the rocker arm (whether central or offset) dictates the leverage ratio and direction of valve opening, but it does not necessitate the use of a push rod. Rocker arms are used in both pushrod and overhead camshaft (OHC) designs; in OHC designs, the cam lobe or follower directly actuates the rocker arm, eliminating the need for a push rod. * **C) two or more valves must be opened and closed at the same time:** While multi-valve designs (like 4 valves per cylinder) require complex valve train systems, the necessity of the push rod is determined by the camshaft location, not the number of valves. Both pushrod and overhead camshaft engines can successfully operate multi-valve systems. * **D) hydraulic valve lash adjusters are used:** Hydraulic valve lash adjusters (lifters/tappets) replace the solid tappet and automatically maintain zero valve clearance. They are often integrated into the push rod system (sitting directly on the cam lobe and supporting the push rod), but the presence of hydraulic adjusters does not *necessitate* the push rod itself. The push rod is necessitated by the physical distance between the cam and the valve gear, regardless of whether the lash adjustment is solid or hydraulic.