1968 Pontiac V8 Engine Description and Operation







ENGINE OPERATION

In 1968 the v8 engine was a complexity of physics yet a simple part of the automobile. Lets run through how it works from start up to idle.
When the ignition switch is turned to start, the battery supplies power to turn the starter

The starter engages the flywheel. The flywheel is bolted to the crankshaft, which is connected to the camshaft by sprockets and a chain (Timing chain). Along the crankshaft are four off set journals. Connected to these journals are the connecting rods, with the pistons pinned a top, inside the cylinder. As the flywheel spins the crankshaft pulls and pushes the pistons form top to bottom in the cylinder. Simultaneously the timing chain on the crankshaft is spinning the camshaft. The camshaft has sixteen eccentric lobes and one gear machined into it. Bolted to the front of the camshaft is another eccentric, used to operate the fuel pump, which applies fuel pressure to the carburetor.

Lifters ride up and down on these off centered lobes. The gear is for turning the distributor. On the bottom of the distributor is a slot for the oil pump shaft. While the camshaft is spinning. The distributor is also spinning the oil pump, providing oil pressure. Lying on top of the each lifter is a push rod, which fits into a cup on the rocker arm. The other side of the rocker arm rests on the top of the valve stem. There are two valves for each cylinder, an intake and an exhaust valve. As the camshaft spins, it pushes the lifters and push rods up. The rocker arm moves upward on its fulcrum, pushing the valve stem down, opening the valve. As the camshaft spins past its high point, the valve springs close the valve and pushes the push rod and lifter down. (See. It's that simple)

With the internal parts spinning, the correct timing of the opening and closing of the valves, in relation to the position of the pistons, is critical. With a piston at top dead center (TDC) both valves are closed. As the flywheel turns and the piston is pulled down, the timing chain spins the cam, which pushes the lifters and the intake valve opens. As the piston is being pulled down, air is being drawn through the air filter. As the air passes through the carburetor into the intake manifold, it meters a small amount of fuel. The fuel-air mixture, from the intake manifold, is pulled through the head passageway, into the cylinder (intake stroke). When the piston reaches the end of its travel and starts upward, the intake valve closes. While traveling upward the fuel-air mixture is now compressed (compression stroke). Now the distributor at this point produces a gap in the points, which causes the ignition coil field to collapse and causes a spark to jump the gap in the spark plug, which is installed at the top of the cylinder head. That spark sets off the fuel-air mixture that was compressed during the compression stroke. The explosion of the fuel air mixture forces the piston down (power stroke). Now the exhaust valve opens and the piston travels upward to expel any brunt gasses. (Exhaust stroke). In summary, while one piston is at top dead center, the other pistons are in different points of their cycle. As the engine's revolutions per minute (rpm) increase, this causes perpetual motion as each cylinder fires. When the engine reaches a sufficient rpm the ignition switch can be released to the run position and the engine will run at idle.

ENGINE OPERATION