General Motors — Base Timing Adjustment (HEI/EST)
Adjustments · Distributor
From a General Motors operator's manual — check it applies to your exact model before use.
Before you start
- If the initial timing connector is connected to B+ while the engine is started, the ignition control module (ICM) may be damaged.
Procedure
- Do not use a timing light that requires piercing of the secondary insulation; use only a timing light with inductive pick-up or jumper type connectors.
- Install timing light at #1 spark plug lead per manufacturer's instructions.
- Do not connect alligator clip lead of the initial timing connector to a B+ source until after the engine is started.
- Start the engine and allow it to warm to operating temperature; connect alligator clip to a convenient B+ source; engine speed should be around 650 RPM.
- Loosen the distributor clamp screw just enough to rotate distributor and set base timing to specification shown for the engine.
- Reduce initial timing if total exceeds limits.
- Secure distributor in position with the clamp screw and tighten to torque specified.
- Recheck timing to assure the distributor did not move during tightening.
- Disconnect the initial timing connector from B+ source and label the connector.
Tools required
- timing light with inductive pick-up Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 454 INITIAL 6° TOTAL 30°
- 350 INITIAL 6° TOTAL 28°
- 262 INITIAL 2° TOTAL 26°
- 181 INITIAL 0° TOTAL 20°
- Idle speed 700 RPM ± 50 RPM
Source: General Motors operator's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.