The valve mechanism opens or closes the intake valve and exhaust valve at the proper timing in order to input the air-fuel mixture into the combustion chamber space and output the combustion gas into the outside. The operation is provided by pear-shaped cams, on a rotating camshaft, driven by a chain or a belt. The camshaft is mounted in the engine block. Camshaft has many small cams with appropriate position on the shaft. It transmits effort to the valve through the cams and metal pushrod. The top of pushrod pushes a rocker arm which bears against the stem of a valve.
The valve mechanism consist of: 1 – camshaft; 2 – pushrod; 3 – valves (inlet valve and exhaust valve); 4 – rocker arm; 5 – valve springs.
Camshaft – is a mechanical component of engine, which rotates, enables the engine to function by opening valves in time with the crankshaft. Camshaft driven by a chain, a belt, or a set of gears from the crankshaft.
Inlet valve – is detail, which allows air-fuel mixture into the cylinder at precise moment.
Exhaust valve – is detail, which allows the spent gases escape at precise moment.
Types of valve mechanisms
Four-stroke engines have valve mechanisms that provide inlet air-fuel mixture and output exhaust the combustion gas. Gas distribution of two-stroke engine is carried out with crank mechanism. Valve mechanisms vary according valves situation in engine block. There are valve mechanisms upper and lower situation.
Upper valve mechanism lives into the head engine and lower valve mechanism lives into the engine block.
Scheme of Valve mechanism for Diesel Engine
1 – Camshaft; 2 – cam follower; 3 – small metal cylinders tappets; 4 – pushrod; 5 – cylinder head; 6 – rocker arm; 7 – lock-nut; 8 – adjusting screw; 9 – valve keeper; 10 – sleeve; 11 – shim; 12 – spring seat; 13 – internal spring; 14 – shim; 15 – exhaust valve; 16 – valve seat.