General Motors GMG-857 — High Energy Ignition (HEI) Distributor Timing
Adjustments
For the General Motors GMG-857, from the General Motors operator's manual.
Applies to: KEM GMG-857, General Motors 5.7L V8 (350 CID) engine
Before you start
- Connecting the initial timing connector to B+ before starting may damage the ignition control module (ICM).
Procedure
- Do not use a timing light that requires piercing of the secondary insulation; use inductive pick-up or jumper type.
- Install timing light at #1 spark plug lead per manufacturer's instructions.
- Do not connect the alligator clip of the initial timing connector to a B+ source until after the engine is started.
- Start the engine and warm to operating temperature.
- Connect alligator clip on long lead of the initial timing connector to a convenient B+ source to remove all advance.
- Loosen distributor clamp screw just enough to rotate distributor and set base timing to specification.
- Secure distributor with clamp screw and tighten clamp screw to torque specified.
- Recheck timing and disconnect the initial timing connector from B+ source.
- Label the initial timing connector by folding the adhesive label over one of the wires.
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
- Engine speed should be around 650 RPM
- Set idle speed to 700 RPM +/- 50 RPM
- Do not exceed initial/total timing limits per engine model
Full service-parts list: KEM GMG-857 →
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.