Automotive camshafts are used in engines to open and close the valves that will help the engine allow entry of air and fuel and release of gases in an efficient manner. The entire action of the valve majorly depends on the shape of the camshaft. Any automotive camshaft is perfect for all engines at one speed but when the speed differs, the engine won’t perform to its full potential with a fixed camshaft. Therefore, automobiles manufacturers have developed different automotive camshaft arrangement that differs as the engine speed changes. There are three typical arrangement of camshaft on engines: Single overhead cam (SOHC), Double overhead cam (DOHC), and Pushrod.

Single Overhead Cam

This is the arrangement where engines rely on a single camshaft per cylinder bank. It denotes an engine with one camshaft per head. In an inline engine, there is one camshaft in the head whereas in valve engine or horizontally-opposed engine which have more than one cylinder head consists of two camshaft, one for each head. Here, the automotive camshaft directly operates the valve through a cam bucket called tappet or an intermediary rocker arm, and springs return the valves into their original position. In heavy engines or in heavy commercial vehicles, the strings have to be really strong because it is the only thing that keep the valves in contact with the rocker arm at high engine speed where valves are pushed down very fast. Volkswagen EG / DX 8v engine is the example of single overhead automotive camshaft.

Double Overhead Cam

As the name indicates, a double overhead camshaft engine have two camshaft located within the cylinder head. Here, inline engines have two camshaft and valve engines have four. One operates the inlet valve and the other operates the exhaust valves. Most of the modern engines are drive by the double overhead camshaft arrangement. It reduces inertia of the valve more as compared to SOHC as there are no rocker arms or reduced in size. Common examples include Riley car engines from 1926-mid 1950s and Harley Davidson Twin Cam engine.

Pushrod Engines

In a pushrod engine, the automotive camshaft are often driven by a short chain or gears and they are less prone to breakage than spring in SOHC engines. Although the valves of a pushrod engine is located above the cylinder in the head, the automotive camshaft is inside the engine block and not on the head. Therefore, it is also known as overhead valve or OHV. Austin Morris A-series engine is an example of OHV.

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