Camshaft

Top Questions

What is the role of a camshaft in an internal-combustion engine?
The camshaft actuates the intake and exhaust valves of piston cylinders, ensuring valve timing is synchronized with piston movement for an engine to run smoothly.

How does the camshaft interact with the crankshaft in a four-stroke engine?
The camshaft is linked to the crankshaft by gears, chains, or a belt, rotating at half the speed of the crankshaft and coordinating valve timing with piston movement.

What are the four strokes in a four-stroke cycle?
The four-stroke cycle comprises the intake stroke, compression stroke, power stroke, and exhaust stroke.

What are the names of the different types of camshafts?
Different types of camshafts are: solid flat tappet, hydraulic flat tappet, solid roller, and hydraulic roller.

camshaft, in internal-combustion engines, a rotating shaft with attached disks of irregular shape (the cams), which actuate the intake and exhaust valves of a piston and cylinder. The cams and the camshaft are usually formed as a unit, with the cams set at angles to open and close the valves in a prescribed sequence as the cams rotate. A separate camshaft for each row of cylinders is driven by gears or chains from the crankshaft. Some engine designs feature two camshafts for each row of cylinders.

Function

The camshaft is mechanically linked to the crankshaft by gears or through chains or a belt so that valve timing (controlled by the camshaft) remains synchronized with piston movement (which drives the crankshaft). The camshaft usually rotates at half the speed of the crankshaft in a four-stroke engine.

As the piston moves up and down, the camshaft opens and closes inlet and outlet valves. This precise coordination is critical for an engine to run smoothly through a typical four-stroke cycle.

The four-stroke cycle

Intake stroke：The opening of a piston cylinder’s inlet valve allows the air-gas mixture to enter the cylinder as the piston moves down in the cylinder.

Compression stroke：The inlet valve closes as the piston rises, compressing the air-gas mixture.

Power stroke：A spark plug at the top of the cylinder ignites the mixture. The force of the generated explosion pushes the piston down. This is where the engine’s power comes from.

Exhaust stroke：The camshaft opens the cylinder’s exhaust valve, allowing the gases to exit the cylinder as the piston comes back up.

Since the camshaft moves at half the speed of the crankshaft, one four-stroke cycle is completed for every two revolutions of the crankshaft.

Types of camshafts

There are four types of camshafts based on the design of the parts connecting the cam lobes to the valves.

• Solid flat tappet：This is a traditional design in which the cam pushes directly on a flat lifter. It works well at high speeds but makes more noise and needs regular adjustment to maintain the correct gap (lash).

• Hydraulic flat tappet：Though similar to the solid flat type, the hydraulic flat has a small oil-filled part inside that automatically keeps the lash correct. This makes it quieter, smoother, and easier to maintain.

• Solid roller：Instead of a flat surface, the lifter has a tiny roller wheel that rides on the cam. This reduces friction and lets the engine use additional cams with more flared-out head curves for more power. Like the solid flat type, it needs regular adjustments.

• Hydraulic roller：This combines the roller wheel, with its reduced friction and greater power potential, with a self-adjusting oil system, which obviates the need for manual lash checks. This design is quiet, durable, and low-maintenance.

Camshafts can also be classified based on the camshaft’s location relative to the valves and how its motion reaches them:

Cam-in-block (overhead valve)：In this design, the camshaft is positioned within the engine block. Pushrods transfer the motion of the cams to rocker arms, which move the valves.

Overhead camshaft：The camshaft is located above the valves in the cylinder head. This eliminates the need for pushrods and allows higher engine speeds.

Single overhead camshaft：One camshaft is used for all cylinders and controls both intake and exhaust valves.

Double overhead camshaft：Two camshafts are used for the cylinders in the engine. One camshaft actuates all intake valves and the other the exhaust valves. This allows greater flexibility in valve timing.

Glossary

Cam lobe：The raised, roughly egg-shaped portion of the camshaft. As it rotates, its shape converts rotary motion into an up-and-down motion to open and close valves.

Tappet (lifter or follower)：A small component that rides on the cam lobe and transfers its motion to the rest of the valve train. It can be a flat or roller type and either solid or hydraulic.

Pushrod：A slender rod used in cam-in-block engines to carry motion upward from the lifter in the engine block to the rocker arm in the cylinder head.

Rocker arm：A small lever that turns to push a valve open when lifted.

Valve：A spring-loaded component in the cylinder head that opens to admit the air-gas mixture (intake valve) or release exhaust gases (exhaust valve) and closes tightly to seal the combustion chamber.

Valve lash (clearance)：Small gap left between the valve train components (usually between the valve stem tip and the rocker arm or follower) when the valve is fully closed and the cam lobe is not actuating valves.

Variable valve timing

The fixed duration for which the inlet and exhaust valves in the piston cylinder open and shut makes for consistent operation, but this has its drawbacks. When the crankshaft rotates at a lower rate, the valves should open and close earlier, whereas if the crankshaft rotates faster they should still open earlier but then stay open for longer. The fixed duration of valve timing cannot accommodate such adjustments. Modern engines often incorporate variable valve timing, in which the camshaft’s phase relative to the crankshaft can be adjusted even as the engine is running.

This system improves power and fuel efficiency across different engine speeds and reduces emissions. Some advanced designs include cam-less or electrohydraulic valve systems, in which manual actuators such as cams are replaced by elements that work on electrical power.