AG Mechanics CDE Practice Exam

A four-cycle engine runs at 3600 rpm's. The number of sparks per minute required at the spark plug would be:

1. 1800

2. 3600

3. 4500

4. 7200

The correct answer is: 1800

In a four-cycle engine, each cycle consists of two revolutions of the crankshaft, so it completes 4 strokes (intake, compression, power, exhaust) in those two revolutions. Since the engine is running at 3600 revolutions per minute (rpm), the crankshaft completes 3600/2 = 1800 cycles per minute. For each cycle in a four-cycle engine, there is one power stroke. This means that there is one spark needed per two engine revolutions, or one spark per cycle. Therefore, at 3600 rpm, the number of sparks required at the spark plug would be 1800 per minute. This explanation is why the correct answer is option A (1800). Options B, C, and D can be ruled out as they do not account for the correct calculation based on the operation of a four-cycle engine as explained above.