Tools You'll Need:
* Timing light: Essential for accurately setting the timing.
* Socket set: To remove and replace the distributor.
* Wrench set: To potentially adjust the distributor.
* Mechanic's gloves: To protect your hands.
* Shop rags: To keep things clean.
* Owners Manual or Repair Manual: For specifications. The exact timing specifications will vary slightly depending on the year and specific application of the 305.
Procedure:
1. Identify the Timing Marks: Locate the timing marks on the crankshaft damper (harmonic balancer) and the timing chain cover. These marks will align at Top Dead Center (TDC) on the #1 cylinder's compression stroke. Consult your manual for the exact location of these marks.
2. Verify #1 Cylinder is at TDC: With the engine off, rotate the crankshaft (using a wrench on the crankshaft bolt – carefully) until the timing marks are aligned. Double-check that the #1 cylinder is actually on the compression stroke. You can do this by:
* Feeling for compression: Using your thumb, carefully feel for compression at the spark plug hole (make sure the spark plug is removed).
* Using a piston stop: A piston stop tool inserted into the #1 spark plug hole will prevent you from accidentally going past TDC.
3. Connect the Timing Light: Hook the timing light up to the #1 cylinder spark plug wire and connect the timing light's power clamp to a good ground.
4. Start the Engine: Have a helper crank the engine while you observe the timing mark on the balancer through the timing light. The illuminated timing mark will show the current timing advance.
5. Compare to Specifications: Your engine's specifications will indicate the proper timing advance at idle (usually in degrees Before Top Dead Center or BTDC). This is often listed as a range (e.g., 6-10 BTDC). Consult your owner's manual or a repair manual for your specific engine.
6. Adjust the Timing (if necessary): If the timing is off, you'll need to adjust the distributor. Loosen the distributor clamp slightly. Then:
* To advance the timing: Rotate the distributor slightly clockwise.
* To retard the timing: Rotate the distributor slightly counter-clockwise.
Re-check the timing after each small adjustment. Make small adjustments until the timing is correct, then tighten the distributor clamp.
7. Double Check: After making your adjustments, restart the engine and recheck the timing to ensure it's stable.
Important Considerations:
* Vacuum Advance: Many 305 engines have a vacuum advance mechanism on the distributor. This can affect the timing at idle. You might need to disconnect the vacuum advance line to set the base timing accurately, then reconnect it afterward.
* Distributor Rotation: Rotating the distributor counter-clockwise will retard the timing, and clockwise will advance it. However, this is relative and depends on the engine and distributor setup. Be careful not to rotate it too far.
* Professional Help: If you're not comfortable working on your engine, it's best to take it to a qualified mechanic. Improper timing can damage your engine.
* Engine RPM: The timing may be different at higher RPMs. The initial timing setting is often the idle timing.
This is a general guide. Always refer to your specific vehicle's repair manual for accurate timing specifications and any special instructions. Safety first! Remember to disconnect the negative battery terminal before starting any work on your vehicle's electrical system.
