ASE A1 Engine RepairGeneral Engine DiagnosisHard
A technician is performing a static ignition timing check on an older vehicle with a distributor. The specification is 8 degrees BTDC (Before Top Dead Center). After connecting a timing light and rotating the distributor, the timing mark aligns at 12 degrees BTDC. What adjustment should the technician make?
- ARetard the timing using the centrifugal advance weights.
- BAdvance the timing using the vacuum advance mechanism.
- CRotate the distributor counter-clockwise.
- DRotate the distributor clockwise.
Show answer & explanationAnswer & explanation
Correct answer: D. Rotate the distributor clockwise.
To retard (decrease) ignition timing from 12° BTDC to 8° BTDC, the distributor must be rotated clockwise. Rotating the distributor clockwise moves the pickup closer to the rotor's firing position later in the engine's rotation.
Why the other options are wrong
- A. Centrifugal advance weights are also dynamic, RPM-dependent adjustments and not manually adjustable for static timing.
- B. The vacuum advance mechanism is a dynamic adjustment, not used for static timing. It's also not a manual adjustment for the technician during a static timing procedure.
- C. Rotating the distributor counter-clockwise advances (earlies) the timing, moving the spark event further from TDC.
Distributor Timing Adjustment
Static ignition timing on a distributor-equipped engine is adjusted by rotating the distributor body. Clockwise rotation retards timing, counter-clockwise rotation advances timing.
- Clockwise retards timing
- Counter-clockwise advances timing
- Set at specific RPM (often idle) with vacuum advance disconnected
Memory trick: Clockwise retards, counter-clockwise advances, don't miss your chances!