FAA Powerplant Written Practice Test

When should magneto breaker points be timed to open?

1. At idle engine speed

2. When the engine is at maximum RPM

3. When the greatest magnetic field stress exists

4. When the ignition coil is charged

The correct answer is: When the greatest magnetic field stress exists

Timing the magneto breaker points to open when the greatest magnetic field stress exists is crucial for optimal engine performance. This timing occurs at a specific point within the rotation of the magneto, just before the magnetic fields generated by the rotating magnet dissipate, allowing for the most effective transfer of energy to the ignition coil. When the breaker points open at this time, a sudden collapse of the magnetic field occurs, inducing a high voltage in the ignition coil. This voltage is essential for creating the spark needed to ignite the air-fuel mixture in the combustion chamber. Identifying the appropriate timing to open the points ensures that the engine receives a strong and consistent spark, which can greatly influence engine performance, starting reliability, and overall efficiency. Achieving the correct timing helps to prevent issues such as misfiring or hard starting, which can stem from weak ignition sparks produced by improper timing. Timing the points to open at idle or maximum RPM wouldn’t align with the mechanical and electromagnetic principles governing the ignition system. Timing them based on the charging state of the ignition coil, while important in understanding the system, is not the moment when the greatest energy is released.