Imperial Homepage -> Repair -> Engine -> Timing Light
Question from Kevin:
Where are you supposed to set the mark to? There's a metal strip that has markings on it, but not sure where to set it.
This sheet metal piece has some markings on it. There is a zero in the middle, and then if I recall 3 marks from each side, 5 degrees each. So, you have reading resolution of 15 degrees befrore and 15 degrees after TDC.
One of the cables of the timing light goes around the plug wire of spark plug of cylinder number 1 (I think that's on the driver side, the one up front, but check to make sure). With engine idling, aim at the harmonic balancer, the little disk of about 1 inch thick that's rotating under this sheet metal piece. You will see a little horizontal groove on the harmonic balancer flashing and appearing motionless. If the little line is below the zero mark, that means you are before TDC (which is where you should be). Now, if you loosen the distributor and rotate it a little, you will see this mark moving up and down. When you rotate the distributor clockwise (the little vacuum advance module is moving towards the front of the car) you are advancing and you will notice the mark is dropping.
What is the optimum setting for your car? Keep on advancing till you hear the engine pinging (on a fully warmed up engine). Dick B. suggests to test for pinging at around 30 mph on D, by pushing the gas on a medium to light acceleration. I do it differently. Since my cars are slightly modified, I never hear pinging in that condition (unless the timing is way too advanced). I do a WOT acceleration throughut the rpm range of the engine w/ 1st or 2nd gear (from 2000 all the way to 4500, no reason to rev it further if you are trying to detect knock). If you don't hear any knocking, advance some more, regardless of what the timing light says (the more you advance, the higher the performance and economy, and the lower the exhaust temperature). When you do start hearing the familiar pinging sound, retard a hair (say one or two degrees) and leave it there. Use the timing light to record this "optimum" setting, so if you have to mess with the timing again, you won't have to go through all that. Its possible that in the summer you may have to retard a hair more. The hotter the engine, the more it tends to ping.
Beware: some real low compression ratio engines that have no carbon deposits (I don't think the 71 is included, I think the 71 has close to 9 which is almost healthy) may never knock, especially when premium gas is used. If you use the above technique, you may end up advancing way too much, which will be beyond optimum. One of the symptoms for this case may be hard starting.
Don't forget to disconnect the vacuum advance.
Your engine should be 9.7-1 compression if it hasn't been modified and and running 91octane gas you probably should be ok at around 5 or 6 btdc...less than halfway down from 0 to bottom of markings plate. If your car came from a low elevation you'll have some carb work to do too.
Question from Remco:
I changed the distributor on my '57. My old one had no mechanical or vacuum advance. Within one hour I had the hold-down plate out and I installed my new distributor, new plugs, new wires, new rotor and cap, and a new coil. I put the new cables on exactly the same as the old ones came off. I set the distributor and started my car. It runs good so I try to set the timing. NO timing mark is in sight. I try to adjust the distributor and the engine almost stalls before I could see the last timing mark. When I adjust it by ear, there are no marks in sight. What am I dooing wrong ???
I think best option is not to use timing light any more and don't bother about is. The car runs fine but I would like to know what I did wrong.
Check to be sure the timing light pickup is on the #1,left front, plug wire, if it is already then the harmonic damper has slipped.
Make sure that your timing light is hooked up to the #1 cylinder. It is the front left cylinder.
You must remove the vacuum line from the distributor while timing, or it will not time right.
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