A technician is timing a magneto to the engine (external timing) rather than performing internal E-gap timing. Which of the following describes this procedure?
- ARotating the crankshaft to the manufacturer's specified degrees before top dead center on the compression stroke, then adjusting the magneto position until the breaker points just begin to open
- BSetting the ignition switch to the BOTH position and verifying no RPM drop occurs
- CSetting the breaker points to open exactly at the moment the rotating magnet is at its neutral position
- DAdjusting the gap between the magneto rotor and pole shoes to the manufacturer's tolerance
Show answer & explanationAnswer & explanation
Correct answer: A. Rotating the crankshaft to the manufacturer's specified degrees before top dead center on the compression stroke, then adjusting the magneto position until the breaker points just begin to open
External (engine-to-magneto) timing is performed by rotating the crankshaft to the specified number of degrees before top dead center on the compression stroke for the timing cylinder, then rotating the magneto housing on the engine until the breaker points just begin to open (often indicated by a timing light), and securing the magneto in that position.
Why the other options are wrong
- B. This describes a magneto operational check (ignition switch/RPM drop check), not the timing procedure.
- C. This describes internal E-gap timing within the magneto itself, not timing the magneto to the engine.
- D. Rotor-to-pole-shoe gap is a magneto internal assembly clearance, unrelated to this timing step.
Magneto-to-Engine (External) Timing
The procedure of positioning the crankshaft at the specified degrees BTDC on the compression stroke, then rotating the magneto on its mounting until the breaker points just open, to synchronize spark timing with piston position.
- Uses crankshaft timing marks/degree wheel and a timing light or buzzer box
- Performed after internal E-gap timing is already set within the magneto
- Ensures spark occurs at the correct crank angle for combustion
Memory trick: Internal E-gap sets the spark inside the mag; external timing lines the mag up with the crank.