TCCA Powerplant Turbine Practice Test 2026 - Free Powerplant Turbine Exam Questions and Study Guide

The correct answer is that the 4 lobe cam ring rotates at half the crankshaft speed due to the mechanical design and function of the camshaft and crankshaft system. In many engine designs, particularly those using multi-lobe cam configurations, the cam ring is typically driven by the crankshaft through a timing mechanism.

When the crankshaft rotates, it completes a full cycle for every two complete revolutions of the cam ring linked to the lobe mechanics of the engine. This means that as the crankshaft makes one full rotation (360 degrees), the cam, which is set up to operate the engine's valves or other components, rotates only 180 degrees, effectively completing one lobe cycle for every two revolutions of the crankshaft. Thus, the cam ring's speed is halved compared to that of the crankshaft.

Understanding this relationship is vital for diagnosing issues in engine timing and operation, as any discrepancies from this expected behavior can indicate problems in the timing belt, chain, or gear mechanism connecting the crankshaft to the cam ring.