OHC vs. SOHC vs. DOHC: What Is The Difference?

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Know More About Engine Terminology - OHC, SOHC, DOHC:

Conventional Valve Operating Mechanism:

Before OHC: In older generation conventional engines, the engine camshaft was located in the cylinder block next to its crankshaft. The engine’s valves were located in the cylinder head at the top. The camshaft operated a range of parts such as the rocker arms, push-rods, and tappets that, in turn, operated the valves.

The conventional valve operating mechanism
The conventional valve operating mechanism

This design is applicable to slower speed engines. It involves many moving parts and results in sluggish engine response. However, the passenger cars needed refined high-speed engines. So, the engineers replaced this technology with a more sophisticated ‘Over Head Camshaft’ design mechanism or the OHC.

What is OHC?

OHC stands for Over Head Camshaft. This valve arrangement configuration places the camshaft in the cylinder head above the pistons and combustion chamber. Such camshaft operates the valves or lifters directly. This is opposed to the conventional design of overhead valves which are operated by ‘rocker arms’ & push-rods.

OHC Enigne
OHC Engine

What is SOHC:

Firstly, the term SOHC stands for Single Over Head Camshaft. This design uses only one camshaft placed in the cylinder head. Typically an in-line engine with a single cylinder head has one camshaft placed at the top of the cylinder head. This is opposed to the bottom position in the cylinder block, which the conventional design used.

How SOHC Works?

Usually, this lone camshaft operates both the inlet and exhaust valves. Using the OHC type of design eliminates the need for some parts such as rocker arms, pushrods, and rocker-arm tubes. This results in a simpler design and smoother and quieter engine operation. It also helps to reduce weight and maintenance costs.

SOHC - 'Single Over Head Camshaft' mechanism
SOHC - 'Single Over Head Camshaft' mechanism

An engine with multiple cylinder heads such as a ‘V-engine' or a flat (horizontally-opposed) engine uses two camshafts, one for each cylinder head. However, this lone camshaft itself operates both the Inlet & Exhaust valves.

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