Any car reference manual can tell you how to set distributor advance with a timing light, and it's one of the first things a mechanic typically learns in Auto Shop 101. However, setting distributor timing by ear is very nearly as lost an art as that of carburettor tuning using lead body filler, and it's one of those little things that separates the men from the boys in any shop. Setting timing by ear is, by nature, a fairly simple procedure that relies more upon mechanic skill than any of those newfangled doohickeys sold at the Sears and Roebuck.
- Skill level:
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Things you need
- Basic hand tools
- Small bolt, screw or golf tee
Fill your fuel tank with the lowest grade of fuel you intend to use. This is crucial since you're going to be setting your ignition advance right at the engine's detonation threshold, and you don't want to set it to work with 93 octane when you usually run 87 octane.
Identify the vacuum advance distributor or ignition module plug on your distributor. Notice that it sits just off the distributor's centre axis and points to either the left or right. The direction that your vacuum advance module points is the direction of ignition advance (usually clockwise) and the other direction is ignition retard.
Warm the engine up to operating temperature. Shut the engine off and unplug the vacuum advance tube from the vacuum advance module on the distributor. Stick a small bolt, screw or golf tee into the tube to plug it. Start the engine, rev it up a little and listen for surging and pinging. If the engine runs normally, you're cleared to proceed. Shut the engine off and loosen the hold-down clamp bolt on the block at the base of your distributor.
Turn the distributor about three degrees in the direction of advance, tighten the hold-down clamp a little and start the engine. If the engine starts fine and runs with no surging or pinging, then shut the engine off and advance the distributor another three degrees. Start the engine and retest. Keep advancing the distributor until the engine struggles to start or surges and pings. You've now reached the advance threshold for initial timing.
Loosen the hold-down clamp and back the timing off by three degrees, or just enough so that the starter spins freely and engine starts easily again. Take the car for a test drive around the block. Accelerate gently and listen for knocking or pinging, feel for drops in power and engine surging. Tighten the hold-down clamp.
Shift the car in a high gear so that the engine lugs a little, or place it in "Drive." Place your foot lightly on the brake pedal to ensure the engine is working against a load. Accelerate a bit harder and listen for knocking --- get off the gas immediately if you hear anything. Park the car and retard the timing by a few degrees. Test drive the car again. If all is well, then fully tighten the hold-down clamp and plug the vacuum advance back into your advance module.
Start the car and go for a test drive to make sure all is in order. Your car should now run at its optimal timing for the fuel you're using and the altitude at which you live.
Tips and warnings
- You can think of degrees of timing like the minutes on a clock. One full distributor rotation is equal to 180 degrees, and there are 60 minutes in an hour. Hence, one "minute" of rotation at the distributor equals three degrees of ignition advance or retard. Rotating the distributor by five "minutes" would equal 15 degrees of advance or retard. So, it should go without saying that it takes a sharp eye and a steady hand to make the incremental changes necessary to set timing by ear.
- This job should not be performed by inexperienced persons. Many modern engines are known as interference engines. That means the pistons will interfere with the valves if not timed properly. Extreme damage could occur.
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