How to Set the Timing on a 350 Engineby Jeffrey Caldwell
Setting the ignition timing on a 350 engine means you synchronize the rotation of the distributor with the rotation of the crankshaft. This ensures that the spark plug at each cylinder fires at the correct time. Every vehicle is equipped with a tuneup decal somewhere inside the engine bay that provides the correct ignition timing value. It will be expressed as a number of degrees before or after top dead center. Use this value to mark the timing tab before checking the timing.
Connecting a Timing Light to a 350 Engine
Disconnect the vacuum hose from the distributor, and plug the line with a bolt.
Connect the positive lead (red) on the timing light to the positive battery terminal on your vehicle. Connect the negative lead (black) on the timing light to the negative battery terminal.
The third wire on the timing light and its clip fits between the No. 1 spark plug and wire. The No. 1 spark plug is the first one on the right as you are facing the engine from the front of the vehicle. Pull the wire off the No. 1 spark plug, and insert the clip from the timing light between the No. 1 spark plug and wire.
Make sure all the electrical leads for the timing light are routed away from any moving parts on the engine and any parts that become excessively hot.
Locate the timing tag on the front of the engine. It will be bolted to the lower end of the timing chain cover. Clean the timing tag using an automotive solvent.
Locate the groove across the crankshaft pulley. You may wish to "bump" the starter to rotate the groove to the top of the pulley. Do this by inserting the key into the ignition and turning the key to start. Quickly turn the key back to the "off" position before the engine can start. Continue until the groove is on top of the pulley.
Use white paint or chalk to highlight the groove on the crankshaft pulley. Also mark the value on the timing tab that represents the correct ignition timing value as specified on the tuneup decal in the engine bay.
Setting the Timing on a 350 Engine
Turn on the engine and allow it to warm up to normal operating temperature. Remember to keep the electrical leads from the timing light clear of the engine.
Point the timing light toward the timing tab and crankshaft pulley. The light will make the timing marks appear stationary.
If the two marks line up, the timing is set correctly. If not, you must adjust the timing.
Adjusting the Timing on a 350 Engine
Shut the engine off.
Slightly loosen the locknut on the distributor clamp at the base of the distributor. You only need to loosen the locknut enough to be able to rotate the distributor.
Turn the engine on.
Aim the timing light toward the timing tab and crankshaft pulley. If the two marks are out of alignment, slowly rotate the distributor until the marks line up.
Shut off the engine.
Tighten the locknut on the distributor clamp at the base of the distributor.
Turn on the engine. Use the timing light to make sure the mark on the timing tab and the groove on the crankshaft pulley are still in alignment.
Turn off the engine. Unplug and then reconnect the vacuum line to the distributor.
Disconnect the timing light from the engine and battery.
- If you have a 350 engine with an H.E.I. ignition system, you may wish to use an inductive timing light. The high voltages used in these systems can cause arcing between the No. 1 spark plug and wire, resulting in false readings when using older-style timing lights. H.E.I. ignition systems were standard equipment on GM vehicles built after 1974.
- When working on an engine while it is running, always be aware of moving parts of the engine, such as the engine fan and drive belts. Also be aware of any parts of the engine that may become excessively hot, such as the heads and exhaust manifolds.