What a Camshaft Does in an Engine

A camshaft times and actuates an engine’s intake and exhaust valves, opening and closing them at precise moments so the cylinders can breathe and expel gases efficiently; it converts the crankshaft’s rotation into the linear motion that moves valves via lobes, followers, and springs, all synchronized by a timing belt, chain, or gears.

Why the Camshaft Matters

Every four-stroke engine relies on a camshaft to coordinate airflow with piston movement. That synchronization determines torque, power, fuel economy, emissions, and drivability. In modern engines, electronically controlled cam phasers adjust that timing on the fly, broadening performance and efficiency.

Core Functions

The camshaft’s essential roles in a four-stroke internal-combustion engine include the following points, which together describe how it governs combustion breathing and timing:

• Opens intake valves to let the air-fuel mixture (or air in diesels) enter the cylinder.
• Opens exhaust valves to expel burned gases after combustion.
• Sets valve timing, duration, and lift via the shape of its lobes, defining when and how far valves move.
• Synchronizes with the crankshaft—rotating at half crank speed in a four-stroke—to match valve events to piston position.
• Enables variable valve timing and lift in modern engines through cam phasers or multi-profile/lift systems.
• Drives auxiliaries on some engines, such as high-pressure fuel pumps for direct injection and vacuum pumps.

Together, these functions control the engine’s breathing cycle, underpinning power delivery characteristics and emissions performance from idle to redline.

How It Works

From Rotation to Valve Motion

The camshaft’s egg-shaped lobes push on lifters (tappets) or followers, which in turn move rocker arms or directly press on valve stems. Valve springs close the valves when the lobe rotates away. In a four-stroke engine, the camshaft rotates once for every two rotations of the crankshaft, ensuring that each valve event aligns with the intake, compression, power, and exhaust strokes. Mechanical synchronization comes via a timing belt, chain, or gearset; sensors track both the cam and crank positions so the engine control unit (ECU) can manage ignition, fuel injection, and variable timing precisely.

Valve Events and Performance

Three parameters define a cam’s behavior: lift (how far the valve opens), duration (how long it stays open), and overlap (when intake and exhaust valves are briefly open together). Higher lift and longer duration can increase high-rpm power by improving cylinder filling, but they can roughen idle, reduce low-end torque, and challenge emissions. Overlap can aid scavenging at high rpm but hurts low-speed efficiency. Modern variable systems mitigate these trade-offs by shifting timing and, in some cases, lift as conditions change.

Designs and Modern Variations

Automakers use different valvetrain architectures and technologies, each with advantages for packaging, efficiency, or performance:

• OHV/pushrod (cam-in-block): The cam sits in the engine block, operating valves via lifters, pushrods, and rocker arms. Compact and torquey, common in many V8s.
• SOHC (single overhead cam): One cam per bank operates both intake and exhaust valves, often via rocker arms—simpler than DOHC.
• DOHC (dual overhead cam): Separate intake and exhaust cams per bank enable optimal valve angles and high-rpm breathing; common in modern multi-valve engines.
• Variable cam phasing (VVT/VCT, e.g., VVT-i, VANOS, i-VTEC phase): Hydraulically or electrically rotates the cam relative to its drive to advance/retard timing for power, economy, and emissions.
• Variable lift/duration systems (e.g., Honda VTEC, BMW Valvetronic, Fiat MultiAir): Switch cam profiles or vary lift continuously to broaden the torque curve and reduce pumping losses.
• Cam-driven auxiliaries: Many direct-injected gasoline engines mount the high-pressure fuel pump on a cam lobe; some diesels and gasoline engines drive a vacuum pump from the cam as well.

Each configuration balances complexity, cost, and results: DOHC with advanced phasing and lift control delivers the broadest capability, while pushrod layouts optimize size and low-speed torque.

Reliability, Maintenance, and Timing Service

Camshafts themselves are durable, typically made from cast iron or billet steel and lubricated by pressurized oil. Their performance depends on clean oil and correct viscosity—both crucial for hydraulic lifters and cam phasers. Timing belts require periodic replacement per the manufacturer’s schedule; timing chains are designed for longer life but can stretch or suffer from guide and tensioner wear. On “interference” engines, a failed belt or chain can allow valves to contact pistons, causing severe damage, so timely service is essential.

Symptoms of Trouble

Camshaft wear, timing errors, or phaser faults produce recognizable signs that indicate the valvetrain may need diagnosis:

• Hard starting, rough idle, misfires, or noticeable loss of power—especially across the rev range.
• Rattling on cold start, often from a loose timing chain or sticky cam phaser/tensioner.
• Check Engine light with cam/crank correlation or phaser codes (commonly P0010–P0017 on many vehicles).
• Poor fuel economy and higher emissions, sometimes accompanied by sulfur/sooty exhaust smell.
• Valvetrain ticking, backfiring, or metal particles in oil indicating mechanical wear.

If these symptoms appear, prompt inspection of timing components, oil condition, and sensor signals can prevent further damage and restore proper valve control.

Context and the Road Ahead

As emissions and efficiency targets tighten, variable cam timing and lift systems have become standard on most new engines, aiding Miller/Atkinson-like strategies in hybrids and improving turbo response. Experimental “camless” systems using electro-hydraulic or electromagnetic actuators (such as FreeValve) show promise but remain rare in mainstream production as of 2025 due to cost, durability, and control complexity.

Summary

The camshaft is the mechanical conductor of an engine’s breathing, converting rotation into precisely timed valve motion. By setting when and how far valves open—and, in modern engines, by varying those events dynamically—it shapes power, torque, efficiency, and emissions. Keep oil fresh, follow timing service intervals, and the camshaft will quietly orchestrate reliable performance mile after mile.

Can you run an engine without a camshaft?

No, a car will not run without a camshaft. The camshaft plays a crucial role in the engine’s operation by controlling the opening and closing of the engine’s valves. This timing is essential for the intake of air and fuel into the combustion chamber and the expulsion of exhaust gases.

What happens when a camshaft goes bad?

When a camshaft goes bad, you might notice symptoms like a rough idle, engine misfires, lack of power, a lit check engine light, a loud ticking or tapping noise from the engine, increased fuel consumption, and difficulty starting the vehicle. These issues arise because a faulty camshaft fails to correctly open and close the engine’s intake and exhaust valves, disrupting the engine’s combustion and timing. 
This video explains the common symptoms of a bad camshaft, including engine misfires and noises: 53sKamsiparts Automotive YouTube · Sep 14, 2023
Common Symptoms of a Bad Camshaft

• Rough Idle and Misfires: The camshaft’s timing is crucial for proper combustion. A worn or damaged camshaft can lead to inconsistent valve operation, causing the engine to run roughly and misfire. 
• Engine Performance Issues: You may experience a noticeable loss of power, hesitation during acceleration, and a general lack of responsiveness from the engine. 
• Check Engine Light: A malfunctioning camshaft can trigger sensors, causing the “Check Engine” light to illuminate on your dashboard. 
• Abnormal Noises: A worn camshaft or damaged camshaft bearings can create loud tapping or ticking sounds, especially from the upper part of the engine. 
• Increased Fuel Consumption: Inefficient combustion due to poor valve timing can lead to a drop in your vehicle’s fuel efficiency. 
• Stalling and Starting Problems: Severe camshaft issues can disrupt the engine’s operation, leading to stalling, particularly at low speeds, or difficulty getting the engine to start. 
• Backfiring: Incorrect valve timing can allow unburnt fuel to ignite outside the combustion chamber, resulting in loud pops or bangs from the exhaust or intake. 
• Metal Shavings in Oil: As the camshaft lobes wear down, they can shed metal particles into the engine oil, which can be seen when draining the oil. 

Why It Matters
A bad camshaft is a serious issue that can lead to extensive and expensive engine damage if not addressed promptly. Early replacement can help restore engine performance, improve fuel efficiency, and prevent further harm to related engine components. 
This video explains the importance of a camshaft position sensor and how it relates to engine timing: 57sCar Care CluesYouTube · Nov 6, 2024

Is a camshaft worth fixing?

Think of your camshaft replacement as preventive medicine for your car. Just as regular check-ups help maintain your health, this repair protects your engine’s vital systems and ensures reliable performance for years to come.

Does a camshaft increase horsepower?

Yes, a performance camshaft can increase horsepower by optimizing airflow into and out of the engine’s cylinders, usually by increasing valve lift or duration to allow more air and fuel to enter the combustion chamber. However, this increase in high-RPM power often comes at the cost of lower-end torque and potentially a rougher idle, so the choice of camshaft should align with the specific needs and intended use of the engine. 
How a Camshaft Increases Horsepower

• Increased Airflow: A performance camshaft is designed with lobes that are “bigger or longer” than stock, which increases valve lift (how far the valves open). This allows a greater volume of the air-fuel mixture to enter the cylinders, leading to more power. 
• Increased Duration: The camshaft also controls valve timing, or duration, which is the amount of time the valves remain open. Longer duration allows more time for the engine to “breathe” and fill the cylinders, boosting high-end power, notes Quora. 
• Engine Breathing: By changing the valve lift and duration, a performance camshaft directly affects how the engine “breathes,” improving the flow of air and exhaust. 

Considerations and Trade-offs

• Power Band: Opens in new tabThere’s a trade-off between low-RPM torque and high-RPM horsepower. A cam optimized for peak horsepower will likely sacrifice some low-end performance. 
• Engine Characteristics: Opens in new tabThe stock camshaft is a compromise designed for a specific balance of performance and drivability. An aftermarket cam changes this balance to suit different goals. 
• Other Modifications: Opens in new tabA camshaft upgrade often works best in conjunction with other engine modifications, such as improved exhaust and intake systems, to fully realize its potential.