FAA Powerplant Written Practice Test

What is a probable cause for a shift in internal timing of a magneto during operation?

1. Electrical interference

2. Worn cam follower and/or pitted breaker points

3. Faulty ignition leads

4. Incorrect installation

The correct answer is: Worn cam follower and/or pitted breaker points

A shift in internal timing of a magneto during operation is most likely caused by a worn cam follower and/or pitted breaker points. The cam follower is a critical component that interacts with the magneto’s cam to ensure proper timing of the ignition spark. If the cam follower becomes worn, it can lead to inconsistent engagement with the cam profile, causing the timing to shift. This shift can affect the timing of the spark relative to the position of the pistons, potentially leading to engine performance issues or misfires. Additionally, pitted breaker points can result in poor electrical contact, which may cause variations in the timing cycle. As the points open and close at different rates due to wear, the ignition timing can become inconsistent. This indicates that maintaining the condition of both the cam follower and the breaker points is crucial for the optimal performance of the magneto and its timing. Other factors like electrical interference, faulty ignition leads, or incorrect installation might contribute to ignition problems, but they do not specifically relate to the internal timing mechanism of the magneto in the same way that wear and pit formation in mechanical components do. Therefore, while they are important considerations for overall ignition system health, they are not the most probable cause for internal timing shifts within the magneto