What Is the Main Function of the Camshaft?

The camshaft’s main function is to open and close an engine’s intake and exhaust valves at precisely timed intervals relative to the crankshaft, controlling how the engine breathes and, therefore, how it produces power, efficiency, and emissions. In modern engines, the camshaft’s role is coordinated electronically and often adjusted on the fly to optimize performance at different speeds and loads.

How the Camshaft Does Its Job

At its core, the camshaft converts rotational motion into linear motion: as the shaft spins, egg-shaped lobes press on lifters, rocker arms, or cam followers to open valves, then allow them to close under spring force. In a four-stroke engine, the camshaft is synchronized to the crankshaft—typically at half speed (2:1 ratio)—via a timing chain, belt, or gears. Layouts vary: overhead cam designs position the camshaft(s) above the valves, while pushrod (OHV) engines place the camshaft in the block and use lifters and pushrods to reach the valves.

The following steps outline how a camshaft controls valve operation through the four-stroke cycle.

1. Rotation: The camshaft rotates in sync with the crankshaft via a belt, chain, or gear drive.
2. Opening: As a lobe’s rising flank meets the follower, it lifts the valve off its seat to admit fresh air-fuel (intake) or expel exhaust gases (exhaust).
3. Peak lift: The lobe’s peak dictates maximum valve opening, controlling how much air can flow.
4. Closing: The lobe’s falling flank allows the valve spring to close the valve, sealing the combustion chamber.
5. Timing coordination: The lobe’s shape (timing, lift, duration) is matched to engine speed and load requirements, aligning with intake, compression, power, and exhaust strokes.

This precisely timed opening and closing is what enables efficient cylinder filling and scavenging, turning crank rotation into useful power with minimal waste.

Why It Matters

Valve timing, lift, and duration dictate how much air an engine can process and how effectively it burns fuel. Cam profiles shape the torque curve, influence drivability, and affect emissions. Many modern engines use variable valve timing (VVT) and, in some cases, variable lift systems to alter camshaft phasing or lobe effect in real time for a broader performance and efficiency envelope.

These are the key outcomes the camshaft directly influences in an internal combustion engine.

• Airflow control: Governs intake and exhaust flow, determining cylinder filling (volumetric efficiency).
• Power and torque: Profile and phasing tune low-end torque versus high-rpm power.
• Fuel economy and emissions: Optimized timing reduces pumping losses and can improve catalytic converter light-off and EGR via valve overlap.
• Engine smoothness: Proper timing supports stable idle and smooth acceleration.
• Compatibility with technologies: Works with turbocharging/supercharging and direct injection strategies to meet power and emissions targets.

Together, these factors explain why the camshaft—and its control systems—are central to modern engine design and tuning.

Related Roles and Modern Variations

Beyond valve actuation, camshafts in some engines drive or coordinate with other systems. In older designs they may drive a distributor or a mechanical fuel pump. In many direct-injection engines, a cam lobe powers the high-pressure fuel pump. Electronic control units use camshaft position sensors to monitor phase relative to the crankshaft, enabling VVT systems (e.g., phasers on intake and/or exhaust cams) and, in some engines, variable lift mechanisms. Common layouts include single overhead cam (SOHC), dual overhead cam (DOHC), and pushrod (OHV) designs; the choice affects engine packaging, RPM potential, and maintenance complexity.

Types of Camshaft Layouts

The following common layouts determine how the camshaft interacts with the valves and other components.

• OHV/pushrod (cam-in-block): Compact, strong low-end torque; uses lifters and pushrods to actuate remote rocker arms.
• SOHC: One overhead cam per bank; typically simpler, may use rockers to actuate both intake and exhaust valves.
• DOHC: Two overhead cams per bank; allows optimal placement and separate timing control for intake and exhaust, often used with multi-valve heads.

Each architecture influences performance characteristics and how easily advanced timing and lift systems can be implemented.

Maintenance and Signs of Trouble

Camshaft reliability hinges on proper lubrication and timing integrity. Regular oil changes protect lobes, followers, and cam phasers. Timing belts must be replaced at manufacturer intervals; chains require good oil and may need tensioner or guide service over time. Failure or severe wear can cause misfires, power loss, or catastrophic damage in interference engines.

Watch for these common symptoms that can indicate camshaft or timing-related issues.

• Rattling on startup or at idle (chain, tensioner, or phaser problems).
• Check-engine light with cam/crank correlation or timing codes (e.g., P0011–P0025, P0016–P0019).
• Loss of power, rough idle, or misfires across the rev range.
• Hard starting, stalling, or poor fuel economy.
• Elevated emissions or failed inspection due to timing faults.

Addressing oil quality, timing drive condition, and sensor accuracy usually restores proper camshaft control and engine performance.

Bottom Line

The camshaft’s primary job is to time the opening and closing of intake and exhaust valves so the engine breathes correctly. Everything from power delivery to fuel economy and emissions hinges on that precise valve control—now often enhanced by computer-managed variable timing and lift systems.

What does a cam do for performance?

A performance cam increases power by altering valve lift and duration, allowing more air and fuel into the combustion chamber and improving the engine’s breathing to boost horsepower, often at the expense of low-end torque and smooth idling. The camshaft’s lobe profile dictates these changes, with higher lift and longer duration creating more power but also potentially causing rougher performance and reduced longevity for the valvetrain components. 
How a performance cam works

• Valve Lift: Opens in new tabA performance cam has a lobe shape that pushes the intake and exhaust valves further open. This increased lift allows a larger volume of air and fuel into the combustion chamber during the intake stroke, and more exhaust gases to escape during the exhaust stroke. 
• Valve Duration: Opens in new tabThis refers to the length of time the valves remain open. A longer duration opens the valves earlier and closes them later, allowing for more air and fuel to enter, which increases the engine’s power potential. 

Impact on performance

• Increased Horsepower: By improving the “breathing” of the engine, a performance cam allows for greater air and fuel intake, which directly translates to more power. 
• Shifted Power Band: Many performance cams are designed to peak at higher RPMs, providing significant power in the upper range of the engine’s speed. 
• Compromises: To achieve higher-RPM power, performance cams often reduce low-end torque and can cause a rougher, less stable idle. 
• Increased Engine Strain: Higher lift and duration put more stress on the valvetrain components (springs, lifters, rocker arms), which can reduce the longevity of these parts if not properly addressed. 

Choosing the right cam 

• Mild Cams: Opens in new tabIdeal for daily driving, prioritizing low-end torque, smooth idling, and good fuel economy.
• Performance Cams: Opens in new tabTailored for racing or enthusiast applications where high-end power is the main goal.
• Moderate Cams: Opens in new tabOffer a good balance between low-end torque and high-end power for street-driven vehicles.

What is the primary function of cam?

Cam is short for camshaft, the engine part that opens and closes the valves to let the air-fuel mixture in and out of combustion chambers. Every engine manufactured today has, if not one, then at least two or more installed. The camshaft’s primary function is to close and open the valves.

What is the main function of a camshaft?

The primary function of a camshaft is to precisely control the opening and closing of an internal combustion engine’s intake and exhaust valves, ensuring that air and fuel enter the combustion chamber and exhaust gases exit at the optimal moments in the engine’s four-stroke cycle. It does this through a rotating shaft with specially shaped lobes that push on other components, which in turn operate the valves, directly affecting the engine’s performance and efficiency.
 
How it Works

1. Rotating Lobes: The camshaft is a rotating rod with a series of egg-shaped “lobes”. 
2. Valve Activation: As the camshaft rotates, each lobe comes into contact with lifters or rocker arms, pushing them to open the valves. 
3. Valve Springs: When the lobe rotates away, valve springs snap the valves shut, allowing the engine to perform its compression and combustion strokes. 
4. Timing: The speed and precise shape of the camshaft lobes determine the timing, duration, and amount of lift for the valves, which is critical for efficient engine operation. 

Why It’s Important 

• Engine Breathing: The camshaft acts as the engine’s conductor, managing its “breathing” process by controlling when air and fuel are drawn in and when exhaust gases are released.
• Performance & Efficiency: By regulating valve timing, the camshaft directly influences an engine’s power output and fuel economy.
• Synchronization: The camshaft’s rotation is synchronized with the engine’s crankshaft, ensuring these crucial events happen in perfect harmony with the piston’s movement.

What happens when the camshaft goes bad?

When a camshaft goes bad, you might notice symptoms like a check engine light, a rough idle, loss of engine power, and cylinder misfires. You may also hear a loud ticking or tapping sound from the engine. Other signs include poor fuel economy, difficulty starting, and stalling. In severe cases, metal shavings can appear in the engine oil. 
Common Symptoms of a Bad Camshaft

• Check Engine Light: The vehicle’s computer may detect a problem with the camshaft’s function, triggering the light. 
• Rough Engine Idle: Inconsistent valve timing can lead to an irregular engine operation. 
• Engine Misfires: Worn camshaft lobes can disrupt valve timing, preventing proper air-fuel mixture combustion. 
• Loss of Power and Performance: Inefficient combustion due to poor valve timing can result in reduced engine power and acceleration. 
• Loud Ticking or Tapping Noises: Worn camshaft lobes can increase valve clearance, causing noises in the valve train. 
• Engine Stalling: In severe cases, especially at low speeds or idle, a bad camshaft can cause the engine to stall. 
• Difficulty Starting: A faulty camshaft can affect the accuracy of sensor data, making it harder for the engine to start. 
• Increased Fuel Consumption: Inefficient combustion leads to less power output, making the engine use more fuel to maintain performance. 
• Backfiring: Incorrect valve timing can allow unburnt fuel to ignite outside the cylinder, causing popping sounds from the intake or exhaust. 
• Metal Debris in Oil: As the camshaft wears, it can produce metal shavings that contaminate the engine oil. 

Why These Symptoms Occur
The camshaft’s primary job is to control the timing of the engine’s intake and exhaust valves. When it goes bad, these valves may not open or close correctly, leading to: 

• Improper Combustion: Opens in new tabValves not opening or closing at the right time leads to incomplete or inefficient burning of fuel. 
• Disrupted Engine Timing: Opens in new tabThe engine’s computer relies on the camshaft for precise timing data. If this data is inaccurate, the engine can’t coordinate spark and fuel delivery properly.