Ignition timing is when the distributor sends an electric spark into the engine to ignite the fuel. This fuel ignition is what powers the car. The sequence in which this happens is very finely balanced, or "tuned," to provide maximum power and economy. When he timing is not set properly the car may experience hard starting, low power or bad gas mileage. Setting the timing is normally an easy task, but sometimes the manufacturer's timing marks are missing or damaged. Setting the timing without any marks is not difficult with the right information and a few common tools.
Mark the spark plug wires for the cylinder number using a short piece of masking tape on each wire. Remove all the spark plugs using the spark plug wrench. The engine will be easier to turn by hand with the spark plugs removed and it's a good time to replace them if required. Remove the valve cover from over the number one cylinder. On a V-block engine this is normally the valve cover on the driver's side. On in-line engines the number one cylinder is the one closest to the front of the car. Check your vehicle's specifications to be sure which cylinder is number one.
Rotate the engine clockwise and observe the valves on the number one cylinder. When both valves are in the up position, insert a screwdriver into the number one cylinder through the spark plug hole. Rotate the engine very slowly back and forth until the screwdriver is at the maximum height. This indicates the number one cylinder is at Top Dead Center or "TDC" on the compression stroke.
Locate the number one spark plug wire on distributor cap and make a tic-mark of this position with a marker pen on the distributor housing. Remove the distributor cap and observe the position of the rotor.
Loosen the distributor hold down bolt and turn distributor until the rotor is lined up with the mark you made in Step 3. Your timing is now set to zero degrees of mechanical timing.
Replace the valve cover using a new gasket. Replace the spark plugs and spark plug wires using the marks from Step 1. You may want to mark the harmonic balancer with a zero point referenced to a fixed point on the engine. A fixed point could be a bolt head or accessory bracket that does not move when the engine is running. Later on this mark can be used as an indicator for stroboscopic timing.
Connect a vacuum gauge to a manifold vacuum source. Most engines will have a port at the base of the carburettor or throttle body where a gauge can be connected. Start the engine and observe the vacuum gauge reading.
Turn the distributor until the maximum vacuum gauge reading is noted. Back off one inch of vacuum from the maximum reading. Tighten the distributor hold down bolt. Normal readings average from 14 to 21 inches of vacuum depending on the condition of the engine.
Test drive the vehicle and listen for pinging noises. Repeat Steps 5 and 6 if excessive pinging is heard, or if there is a significant loss of power. The timing is correct when the vehicle operates at maximum power without the engine hard starting, backfiring, or pinging on acceleration.
A fender cover or old blanket will protect the finish of your car when working under the bonnet.
Keep body parts, tools and loose clothing away from moving engine parts. Car exhaust fumes are toxic, work only in a well ventilated area.