Tools You'll Need:
* Timing light: This is essential. It's a specialized light that flashes in sync with the ignition pulses, allowing you to see the position of the crankshaft pulley.
* Socket wrench and extension: To remove the distributor cap if needed.
* Spark plug wrench: Possibly needed for initial spark plug wire removal/replacement, depending on access.
* Distributor clamp (optional but recommended): This helps you keep the distributor from moving.
* Shop rags: To keep things clean.
* Owners Manual or Repair Manual: Crucial for getting the correct timing specification for your specific engine and year.
Procedure:
1. Safety First: Disconnect the negative (-) battery cable before starting any work on the ignition system.
2. Locate Timing Marks: Find the timing marks on the harmonic balancer (crankshaft pulley) and the timing pointer on the engine block. The balancer will have degree markings.
3. Set Engine to TDC (Top Dead Center) on the Compression Stroke of Cylinder #1: This is the most crucial step. Your engine's manual will guide you through this. Common methods involve inserting a screwdriver or similar tool into the spark plug hole of #1 cylinder and turning the engine over until the piston reaches top dead center on the compression stroke (the piston moves up and you feel compression). There are also ways to do this using the distributor and rotor position in conjunction with the timing marks.
4. Connect the Timing Light: Attach the timing light's clamp to a spark plug wire. Usually, the number 1 wire is chosen. The other end plugs into the timing light and your vehicle's battery or power source.
5. Start the Engine: With the engine running and the timing light aimed at the timing marks, you'll see the timing marks illuminated by the light flashes. The illuminated mark on the harmonic balancer should align with the timing pointer on the engine block, this will indicate your current ignition timing.
6. Adjust Timing (If Necessary): This is usually done by loosening the distributor clamp and rotating the distributor. Rotating the distributor clockwise advances the timing; counterclockwise retards it.
7. Check the Manual for Spec: Your vehicle's service manual will give you the specific base ignition timing (usually expressed in degrees before Top Dead Center, or BTDC). This is often measured at idle. This is likely around 6-10 degrees BTDC but can vary depending on the year and model. Some engines have specifications that depend on vacuum advance being connected or disconnected.
8. Fine Tuning: After you've set the base timing, you might need to check the vacuum advance and mechanical advance. The manual will tell you what to expect.
9. Reconnect Battery Cable: Once you're satisfied with the timing, reconnect the negative battery cable.
Important Considerations:
* Vacuum Advance: Many 350 Chevy engines have a vacuum advance mechanism on the distributor. This changes the timing automatically depending on engine load. Your timing should be checked with the vacuum line connected and disconnected.
* Mechanical Advance: This is an internal mechanism in the distributor that advances the timing as engine speed increases. While you can't directly adjust this, a faulty mechanical advance can affect the timing significantly.
* Computerized Ignition Systems: If your 350 Chevy has a computer-controlled ignition system (like HEI distributors in later models), adjusting the timing might be more complex and may require specialized tools or software. You might even find the timing is self-adjusting. Always consult your service manual.
* Professional Help: If you're not comfortable working on your engine's ignition system, take your vehicle to a qualified mechanic. Improper timing can cause significant damage.
This information is for guidance only. Always refer to your vehicle's service manual for the precise timing specifications and procedures. Incorrect ignition timing can cause engine damage. If you are unsure about any aspect of this process, seek professional help.
