Valve actuation in overhead-valve engines The cam lobe motion is transmitted to the rocker arm, which oscillates and presses the valve against the spring, opening it against spring force. Is this description correct?

Introduction / Context:
Valve trains convert camshaft rotation into linear valve motion. Understanding how cams, followers, rocker arms, and springs interact helps diagnose noise, lash, and timing problems.

Given Data / Assumptions:

• Overhead-valve (OHV) or overhead-cam (OHC) systems may use rocker arms.
• Valve springs keep valves seated when not actuated.
• Cam profile dictates lift, duration, and timing.

Concept / Approach:
As the cam lobe rotates, its rise pushes on a follower/tappet, transmitting force to a rocker arm. The rocker pivots and pushes the valve stem downward, overcoming the spring force and opening the valve. When the cam returns to base circle, the spring closes the valve.

Step-by-Step Solution:

Verification / Alternative check:
Service diagrams show rocker ratio and valve lift versus cam lift; lash setting confirms mechanical linkage behavior.

Why Other Options Are Wrong:

• Limited to intake or high rpm only: incorrect; the same mechanism applies to intake and exhaust over all speeds.
• False for OHC: many OHC engines still employ finger followers/rockers with similar action.

Common Pitfalls:
Incorrect valve lash causing noise or burning; weak springs causing valve float; worn cam lobes reducing lift.

Final Answer: