The Crankshaft
Engine crankshafts are like bicycle crankshafts because they transfer up-and-down forces-the pistons being forced through the bore by the air/fuel explosion-into a rotating motion causing your wheels to spin. Cranks have offset throws, exactly like your bicycle's crank except the rods and pistons serve the same function as your legs do: they push the upward throw downward as the piston is pushed the same direction through the bore by the air/fuel explosion. This is what makes your car go. Once the piston goes down, the crank rotates and the piston is moved up again until it reaches the top where it can be pushed down once more by another air/fuel explosion. The crank rotates on its main journals on an oil-filmed sleeve bearing (the main bearings) just like the rods have for their big ends.
 |  The crankshaft rotates on...  The crankshaft rotates on its main journals atop oil-filmed sleeve bearings. A separate set of rod bearings allow the crank journals to spin within the connecting rods' big ends. |  The block houses the reciprocating...  The block houses the reciprocating components that help make the gasoline explode. Pistons slide up and down the bores and the number of bores equals the number of cylinders. The block also contains passages for cooling and lubrication. Notice the main bearing saddles that support the crankshaft. |
The cylinder head's combustion...
The cylinder head's combustion chambers contain the explosive forces needed for igniting the air/fuel mixture that ultimately drives the pistons downward.
The Cylinder Head
Honda cylinder heads are aluminum castings that cap off the tops of engine blocks. They house the spark plugs, combustion chambers, valves and valvetrain. The head must contain the explosive force for igniting the air/fuel mixture in order to drive the pistons downward and not escape. The combustion chambers are integrated within the cylinder head, which is where the valves and spark plugs are located. When looking at a cylinder head's underside (the side that mates to the block) the combustion chambers are the depressions that line up with the bores. It's inside these chambers, when the piston's at the top of its stroke, that the air/fuel mixture is ignited, kicking off the power stroke. The cylinder head also has cooling jackets filled with circulated water, which helps keep combustion chambers from overheating. The cylinder head contains the intake and exhaust ports, which are the passages where intake air and exhaust fumes pass when they're entering and exiting the cylinders.
The Valvetrain
Modern OHC (overhead camshaft) engine heads contain the intake and exhaust valves; both are spring-loaded poppet valves. The springs hold the valves shut but allow them to open with a push. The intake valves open to admit the explosive air/fuel mixture into the combustion chamber. They close to let the engine build compression as the piston, driven by the crank, reaches TDC (top dead center)-the point where the piston reaches the top of its stroke. When the spark plug ignites the mixture and the subsequent explosion drives the piston downward, the exhaust valves open near the bottom of the piston's stroke allowing burnt gasses to escape, preparing the combustion chamber for the next charge of fresh air and fuel.
Valves open and close with...
Valves open and close with the help of camshafts. Camshafts are basically rods with off-center bumps, or lobes, that spin inside the cylinder head at half the speed of the crankshaft.
Valves open and close via camshafts, which are basically rods with off-center bumps or lobes that spin inside the cylinder head at half the crankshaft's speed. The camshaft's lobes push the valves open and closed to admit both air and fuel and to expel exhaust. Some cam lobes work directly on the valves, like with many motorcycle and certain race engines. Typically, the camshaft works the valves through a rocker arm, which is like a miniature teeter-totter. One end of the rocker arm rubs on the rotating camshaft while the other end pushes the valves open and closed. The Honda engines you're familiar with use rocker arms.
Lucky Honda engines feature...
Lucky Honda engines feature VTEC-Honda's highly effective variable cam timing system. The system affords the intake and exhaust cams two sets of lobes, one set optimized for low-rpm effectiveness, the other for high-rpm use. Honda's i-VTEC is similar but also allows for intake camshaft phasing adjustments on the fly for an ever-broader powerband.
Honda engines are overhead cam engines, which means the camshaft is contained within the cylinder head on top of its valves. This is different than OHV (overhead valve) engines like the low-revving, domestic V-8 with its block-located camshaft, connecting to its valves with lifters, pushrods and rocker arms. OHC engines are better suited for high-rpm, small displacement sport compact engines because they have simpler, lighter, more direct acting valvetrains. These valvetrains work better at higher engine speeds because their lower inertial mass allows them to follow the camshaft's lobes more accurately.