Oilers/Plant Tenders (HHC) Civil Service Practice Exam

At what speed does the camshaft of a 4-stroke cycle diesel engine rotate in relation to the crankshaft?

1. Same speed as the crankshaft

2. Twice the speed of the crankshaft

3. Half the speed of the crankshaft

4. Variable speed compared to the crankshaft

The correct answer is: Half the speed of the crankshaft

In a 4-stroke cycle diesel engine, the camshaft typically rotates at half the speed of the crankshaft. This is due to the engine's operational design, where the crankshaft completes two full revolutions for every one complete cycle of the valves, which are controlled by the camshaft. To elaborate, during each complete cycle of the 4-stroke engine—intake, compression, power, and exhaust—there are two revolutions of the crankshaft. However, the camshaft only needs to rotate once to operate the valves properly in harmony with the crankshaft's movement. As a result, the camshaft's speed is effectively half that of the crankshaft, leading to its responsible timing and operation of the engine's intake and exhaust cycles. This mechanical relationship is key in understanding engine dynamics, making the information relevant for anyone working with or studying internal combustion engines, whether for maintenance, engineering, or examinations in the field.