FAA Powerplant Written Practice Test

When installing a magneto, what critical step must occur regarding the piston position?

1. The piston must be at top dead center

2. The piston must be a prescribed number of degrees before top dead center on the compression stroke

3. The piston must be at bottom dead center

4. The piston position is not important

The correct answer is: The piston must be a prescribed number of degrees before top dead center on the compression stroke

In the installation of a magneto, it is crucial to have the piston positioned at a specific point relative to top dead center, particularly on the compression stroke. This positioning ensures that the ignition timing is correct. When the piston is a prescribed number of degrees before top dead center on the compression stroke, it allows the magneto to fire at the appropriate moment in the engine's cycle. This timing is essential for optimal engine performance because it ensures that the fuel-air mixture is ignited at just the right point to maximize power and efficiency. Igniting too early or too late can lead to engine knock, reduced performance, or even damage over time. The other options do not reflect the necessary timing for successful magneto installation. For example, having the piston at top dead center does not account for the timing required for proper ignition since firing at this point could miss the optimal moment. Similarly, having the piston at bottom dead center would not align with the required timing for the ignition cycle. Stating that the piston position is not important overlooks its critical role in ensuring proper operation of the ignition system in the engine.