While installing a magneto, a technician confirms the breaker points just begin to open (correct E-gap) when the No. 1 piston is at the specified degrees BTDC, but notices the distributor rotor is not aligned with the No. 1 terminal segment in the distributor block. What action should the technician take to correct this?
- AWiden the breaker point gap until the rotor rotates into correct alignment with the segment
- BReplace the magneto condenser, since rotor misalignment indicates internal capacitor failure
- CDisengage and reindex the magneto drive gear one spline/tooth so the rotor aligns with the No. 1 segment while the points still open at the correct E-gap
- DAdvance the ignition timing further to compensate for the rotor misalignment
Show answer & explanationAnswer & explanation
Correct answer: C. Disengage and reindex the magneto drive gear one spline/tooth so the rotor aligns with the No. 1 segment while the points still open at the correct E-gap
Because a magneto drive gear can typically be installed in more than one indexed position, the points may open at the correct crankshaft angle while the rotor is misaligned with the correct distributor segment. The technician must disengage the drive and reindex it one tooth/spline at a time until both conditions are satisfied simultaneously: correct point opening (E-gap timing) and correct rotor alignment with the No. 1 segment.
Why the other options are wrong
- A. Changing the point gap alters spark timing but will not correct which segment the rotor points to.
- B. Rotor misalignment is a mechanical indexing issue, unrelated to condenser condition.
- D. Advancing timing further does not correct a mechanical rotor/segment misalignment.
Distributor Rotor-to-Point Timing Alignment
When timing a magneto to the engine, the drive gear must be indexed so the points open at the correct crankshaft angle AND the rotor aligns with the correct distributor segment for that cylinder.
- A magneto drive gear can often be installed in several tooth positions.
- Correct point-opening angle alone does not guarantee correct rotor alignment.
- Reindexing the gear one tooth at a time resolves both requirements together.
Memory trick: Right spark, wrong segment? Shift the gear one tooth to hit the target.