Single Overhead Camshaft (SOHC)
An engine configuration where a single camshaft is located in each cylinder head, operating both intake and exhaust valves.
Single Overhead Camshaft (SOHC) is a cylinder head configuration where a single camshaft is mounted directly above the cylinders. In this layout, the single camshaft controls both the intake and exhaust valves. In V-type engines (like V6 or V8 engines), a SOHC design will have two camshafts in total—one located in each cylinder head bank.
Because a single camshaft must operate all the valves, SOHC engines typically use rocker arms to translate the cam lobe profiles to the valve stems, especially in multi-valve configurations (like 3 or 4 valves per cylinder). SOHC systems are mechanically simpler and narrower than DOHC designs, making them lighter and cheaper to manufacture. However, they offer less flexibility for variable valve timing adjustment because the intake and exhaust lobes are fixed on the same shaft.
Symptoms of SOHC valvetrain issues include ticking noises from the cylinder head (indicating excessive valve lash), engine misfires, and loss of power. Diagnosing valvetrain noise involves removing the valve cover to inspect the camshaft lobes and rocker arms for wear, and adjusting the mechanical valve lash if required. Like DOHC, maintaining the timing belt or chain is critical to avoid engine destruction in interference designs.