"I love it when a plan comes together!" Setting the initial timing is a very simple procedure, once the mechanical principles of the engine are understood. Now comes the fun part- - - - -tweaking that initial setting for best overall performance. There are actually three timing settings, and the only one that's easily adjustable is the first one- - - -initial timing. Once the engine is running, we're partway to the goal. The next step depends on the kind of timing light you have.
A timing light works by flashing as a spark plug fires, effectively freezing the motion of the flywheel or harmonic balancer and allowing the position of the timing mark to be observed in relation to the pointer or a degree scale mounted to the engine block. The "pointer and ball" that stovebolt sixes use has a relationship that varies according to the year of manufacture and the size of the engine, but most of them align when the crankshaft is 5 degrees of rotation before the piston reaches top dead center. By simply aligning the pointer and ball with the timing light, your timing at idle speed will be 5 degrees before top dead center (BTDC). Since the window in the bellhousing is pretty wide, you can vary that relationship a little if you desire. Moving the ball to the left of the pointer advances the timing- - - -going to the right retards it. I've found that most stovebolt engines run best with the leading edge of the ball just touching the pointer- - - -not centered on it. That's probably somewhere in the neighborhood of 7-8 degrees of advance at idle.
Now comes the fun part- - - - -as the engine speed increases the spark needs to happen sooner, so the pressure wave from the burning fuel meets the top of the piston to get the right thrust on it at the most efficient point. The speed of the flame front across the combustion chamber is fairly constant, as long as the fuel mixture doesn't go lean. For now, let's assume the carburetor is supplying the right mixture. The speed of the piston is variable, so firing the plug as much as 30-40 degrees BTDC is required for best performance at cruise speed. Then there's engine load- - - - -light throttle cruise on level ground can tolerate more timing advance than when passing, climbing hills, or hauling a heavy load in the bed, or trailer towing. There are two timing advance modes built into the distributor to accommodate those situations.
