Jim Smart
November 1, 2002
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With eight separate engines working together on a common crankshaft, we have a continuous distribution of power from eight cylinder bores. The distributor makes it possible to fire these eight cylinders in proper order. When we tie the distributor to the camshaft and crankshaft, it all works together in near-perfect synch.

Understanding Old Sparky

We know the ignition system has to fire multiple spark plugs in a timed sequence. Each spark plug has a small gap between the center electrode and cross electrode. Vintage Fords typically have a spark plug electrode gap of .034-inch, suitable for low-energy, point-triggered ignition systems. To get a spark to jump any sized gap, we need high-voltage electricity powerful enough to jump the gap. We produce high-voltage electricity via the ignition coil, which is an electrical transformer that transforms battery voltage (12-14 volts) to high-voltage electricity (around 20,000 volts).

Inside conventional point-type distributors, the ignition points act as a switch for the ignition coil's task of producing high-voltage electricity. When the points open, the ignition coil releases the store of electricity to the distributor's high-tension lead. Because this is a timed sequence, the distributor rotor will be positioned on a given cylinder's spark plug wire lead when the points open. With a V-8 engine, this happens eight times in two revolutions of the crankshaft. With electronic ignition, a magnetic pickup module inside the distributor takes the place of ignition points and condenser. This is oversimplified, of course, because there is also an ignition amplifier separate from the distributor that works hand-in-hand with the pickup module.

The four-cycle power process would be easy to handle if all we had to worry about was firing a spark plug when the piston reached the top of the cylinder. But if we fired the spark plug when the piston reached top-dead-center (TDC), we wouldn't make the most of the fuel/air mixture. Because fuel takes a given amount of time to ignite and burn, we have to fire the spark plug before the piston reaches the top of the cylinder. Fuel and air don't "explode" in the combustion chamber. The fuel/air mix ignites in a "quick fire" that begins at the spark plug and roars across the top of the piston. This is called a flame front.

As engine speed increases, the spark has to occur earlier in the compression stroke. Because we're locating the spark earlier in the compression stroke, this is called "advancing" the spark. How do we advance the spark? We do this with two functions inside the distributor-vacuum advance and centrifugal advance. Centrifugal advance works with the speed of the engine. Vacuum advance works when we lean on the throttle. Both work together to adjust spark timing in line with engine power demands.

Centrifugal advance works with engine speed via springs and flyweights that position the distributor rotor. The faster the distributor turns, the further out the flyweights move against spring tension, positioning the rotor earlier in the compression stroke. Spark timing happens in degrees of crankshaft rotation and piston location. Crankshafts rotate 360 degrees in a full circle. As the piston makes its way up the cylinder bore on compression stroke, this happens between zero and 40 degrees of crank rotation before the piston reaches the top of the bore.

At idle speed, we want the spark to occur at 6 to 12 degrees (crank rotation) before the piston reaches the top of the cylinder. This is called BTDC (Before Top Dead Center). When the engine revs to 3,500 rpm and higher, the spark needs to happen earlier around 36 to 40 degrees BTDC. This helps our engine make the most of the fuel/air charge. When we move the spark any earlier than 40 degrees BTDC-and this is pushing our luck-we risk premature combustion (pinging and detonation) that can do serious engine damage.

Cooling It

All that heat energy released in each combustion chamber during power stroke can be destructive if it isn't controlled. We control the heat with water jackets around the cylinders and in the cylinder heads. Water jackets contain the coolant mix that keeps our engine temperature stable. This is done with coolant, the radiator, a thermostat, hoses, water pump, and a fan that pulls outside air through the radiator.

Coolant flows into the engine's water jackets via the bottom radiator hose. Ideally, we have water jackets that are completely full of coolant, without air bubbles that cause hot spots. The thermostat is a flow-control valve that opens when the coolant temperature in the engine reaches either 180 or 192 degrees Fahrenheit. Older Mustangs have a 180-degree thermostat. Newer, computer-controlled Mustangs are 192 degrees.

When the thermostat opens, it allows hot coolant to leave the engine and flow into the radiator through the upper hose. Coolant in the radiator is displaced by the incoming hot coolant from the engine. Fresh coolant in the radiator enters the engine, which closes the thermostat. The cycle begins all over again when coolant inside the engine reaches 180 or 192 degrees.

Lube It Or Lose It

Another engine survival tool is the oiling system. Engine oil is stored in the oil pan at the bottom of the engine. When we check oil, we're pulling a dipstick that shows us how much oil is in the pan. The camshaft we mentioned earlier also has the busy task of turning the oil pump that keeps our engine alive. It does this through a shaft splined into the distributor shaft.

Our Mustangs have what is called a "G" rotor oil pump that draws oil from the pan and forces it into the oil galleys that feed moving parts like crankshafts and camshaft bearings, pistons and cylinder walls, lifters, rocker arms, timing gearset, and more. Oil is fed to these critical moving parts under pressure, which keeps them from rubbing together. Moving parts float on a layer of engine oil. Think of engine oil as a barrier that protects moving parts from certain destruction.

Another thing engine oil does is cool hot engine parts. As oil flows through the engine, it carries heat away from the hottest parts, such as bearings, pistons, rings, and even valve stems. Engines fail whenever oil pressure is lost and moving parts grind themselves to an unpleasant halt.