How does overhead cam engine work

The 4 stroke cycle starts over again and continues so long as the vehicle is running. All of these strokes are happening very fast, and the speed is referred to as RPM or rotations per minute. The higher the RPM, the faster the engine is operating and rotating the crankshaft. At high RPMs, the 4 stroke cycle can occur hundreds of times a second.

The camshaft is what opens and closes the intake and exhaust valves to suck in air and force it out during this process. Overhead valve or pushrod engines are typically found in older vehicles or larger engines.

The camshaft is installed inside the engine block and is operated through lifters, pushrods, and rocker arms. It is difficult to precisely control valve timing at higher RPM and is better suited for V8 or larger engines. They are lower cost and offer high torque at lower RPM. Single overhead cam or overhead cam engines have a single camshaft installed in the cylinder head.

The valves are operated directly by the camshaft and it is much easier to maintain precise timing at higher RPM and 3 or 4 valves per cylinder. One or Two exhaust valves are operated by the camshaft while two intake valves are operated by oil pressure. If the gap is too large, the valves open late and close early, reducing power and increasing engine noise. Too small a clearance prevents the valves from closing properly, with a consequent loss of compression.

Some engines have self-adjusting tappets, which are hydraulically operated by the engine oil pressure. The overhead valve system OHV system, operated by pushrods, has the crankshaft adjacent and parallel to the crankshaft in the cylinder block.

As the crankshaft rotates, each valve is opened by means of a tappet, pushrod and rocker arm. The valve is closed by spring pressure. The camshaft drive-chain sprocket has twice as many teeth as the crankshaft sprocket, so that the camshaft rotates at half engine speed. An overhead-cam OHC engine needs fewer parts to operate the valves. The cams act directly on bucket tappets or on short levers - known as fingers - which in turn act directly on the valve stems.

The system dispenses with the extra weight and mechanical complexity of pushrods and rocker arms. A long chain is frequently used to drive the camshaft from a sprocket on the crankshaft, but such a long chain tends to 'whip'. The problem is overcome in some designs by fitting intermediate sprockets and two shorter drive chains, kept under tension. The engine can make more power if more air enters the cylinder, and it wastes less power if it is easier to pump the exhaust out of the cylinder.

At higher engine speeds, the engine pumps a lot of air though the cylinders. Having four valves per cylinder allows the engine to pump enough air to run and make useful power at these higher speeds. Another interesting thing that some car makers do is have a separate intake runner for each of the two intake cylinders. One of the intake runners is wide and short for maximum airflow, the other is a tuned intake runner. When the intake valve is open on the engine, air is being sucked into the engine, so the air in the intake runner is moving rapidly toward the cylinder.

When the intake valve closes suddenly, this air slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder.

When it reaches the end of the intake runner, where the runner connects to the intake manifold, the pressure wave bounces back down the intake runner. If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder -- effectively acting like a turbocharger. A DOHC engine is a dual overhead camshaft engine, or an engine with two camshafts.

What is the advantage of a DOHC engine? The biggest advantages of a DOHC engine are increased power and increased speed. This type of engine can particularly increase your vehicle's engine power at high speeds.