FAA Powerplant Written Practice Test

What is a probable cause of a shift in the internal timing of a magneto?

1. Lack of fuel

2. Cam follower wear and/or breaker points wear or pitting

3. Incorrect installation

4. Temperature variations

The correct answer is: Cam follower wear and/or breaker points wear or pitting

A shift in the internal timing of a magneto is most commonly caused by cam follower wear and/or breaker points wear or pitting. The magneto relies on precise timing to create spark at the correct moment in the engine cycle, and any wear or deterioration of the cam follower can lead to inconsistencies in the timing. As the cam follower wears down, its ability to accurately follow the contours of the cam may diminish, which can cause the ignition timing to shift. Similarly, wear or pitting on the breaker points can interfere with the functioning of the magneto, leading to improper contact and a misalignment in the timing. In contrast, factors such as a lack of fuel, incorrect installation, or temperature variations might affect engine performance, but they do not directly result in a mechanical change to the timing of the magneto itself. Therefore, the degradation from wear is the most direct and probable cause of any timing discrepancies within the magneto system.