What Is the Purpose of the Camshaft?

The camshaft opens and closes an engine’s intake and exhaust valves at precisely timed intervals, synchronized with the crankshaft, to control how air and fuel enter the cylinders and how exhaust gases exit. By governing this “breathing,” the camshaft directly shapes power delivery, efficiency, emissions, and drivability.

How a Camshaft Works

At its core, the camshaft converts rotational motion into linear motion using egg-shaped lobes that press on lifters, pushrods, or rocker arms to actuate valves. This motion must be perfectly timed to piston movement to avoid contact and to optimize cylinder filling and scavenging.

1. Rotation: The camshaft turns, typically at half the crankshaft speed in a four-stroke engine.
2. Lobe action: Each cam lobe’s profile (shape) dictates how far and how long a valve opens.
3. Valve actuation: Lobes press on followers/lifters and rockers (or direct tappets) to open valves; springs close them.
4. Synchronization: A timing belt, chain, or gears keep cam(s) and crankshaft aligned to specified timing marks.
5. Feedback/control: Camshaft position sensors report cam angle to the engine control unit (ECU) for precise ignition, injection, and variable timing control.

The interplay of lobe geometry and precise synchronization determines when and how effectively the engine breathes across the rev range.

Key Functions and Impacts

Beyond simply opening and closing valves, the camshaft influences multiple facets of engine performance and compliance.

• Airflow management: Controls intake charge and exhaust scavenging, affecting torque and horsepower.
• Combustion efficiency: Proper timing improves fuel economy and responsiveness.
• Emissions control: Optimized valve events reduce unburned hydrocarbons, NOx, and particulate formation.
• Idle quality and drivability: Overlap and duration affect smoothness at low rpm versus high-rpm power.
• Accessory drive: In many engines, the camshaft drives a distributor (older designs) or a high‑pressure fuel pump (modern direct-injection engines).

The camshaft’s profile and timing strategy are central to balancing performance demands with regulatory and efficiency requirements.

Camshaft Placement and Designs

Engine architecture determines how a camshaft interacts with the valvetrain, influencing complexity, friction, and RPM potential.

• OHV/pushrod: Camshaft in the block; pushrods and rockers actuate valves (compact, strong low-end torque, limited high‑rpm breathing).
• SOHC: Single overhead camshaft per bank; simpler, can use rocker arms to actuate multiple valves.
• DOHC: Dual overhead cams per bank; typically enables four valves per cylinder and finer control of intake/exhaust timing.
• Camless concepts: Electrohydraulic or electromagnetic actuators remove cams entirely; promising prototypes exist, but mass-market adoption remains limited.

While OHV engines remain popular in some V8s, DOHC layouts dominate modern high-specific-output and efficiency-focused designs.

Valve Timing Technologies

Modern engines vary valve timing and lift to widen the torque curve and improve efficiency without sacrificing emissions compliance.

• Cam phasing (VVT): Continuously adjusts the cam’s phase angle relative to the crankshaft via oil‑controlled or electric phasers (e.g., VVT-i, VANOS, VCT, VVT-iE).
• Variable valve lift: Alters lift/duration with multi-step or continuous mechanisms (e.g., VTEC, Valvetronic, MultiAir) to reduce pumping losses and boost power.
• Profile switching: Selects different lobe profiles at specific RPM/load points (e.g., performance cam lobes engaged at higher revs).
• Cylinder deactivation coordination: Works with lifter collapse systems on some engines to reduce fuel use under light loads.

These systems let one engine behave like several, prioritizing smoothness and economy at low load and maximum breathing at high load.

Relationship With the Crankshaft and Timing

Because the pistons and valves share the same space at different times, precise synchronization is critical. In four-stroke engines, the camshaft turns at half the crankshaft’s speed. Timing chains, belts, or gears maintain alignment; failure or skipped teeth can cause power loss or catastrophic damage in “interference” engines where valves and pistons can collide. Regular timing belt replacement (where applicable) and attention to chain tensioners and guides are essential.

Maintenance, Wear, and Failure Symptoms

Camshafts and followers depend on clean, correctly specified oil and proper break‑in to prevent wear. As tolerances are tight, early warning signs should be addressed promptly.

• Symptoms: Ticking/knocking from the top end, misfires, rough idle, loss of power, metal shavings in oil, poor fuel economy, and illuminated check‑engine lights.
• Common causes: Oil starvation or low pressure, extended oil-change intervals, incorrect oil viscosity or additives, unsuitable flat‑tappet break‑in practices, and high-pressure fuel pump lobe wear on some direct-injection engines.
• Diagnostics: Scan for cam/crank correlation codes (e.g., P0010–P0017), inspect timing alignment, check oil pressure, and evaluate cam lobe and follower surfaces.
• Prevention: Use OEM‑spec oil and intervals, replace timing belts/tensioners on schedule, and ensure proper lubrication after major engine work.

Proactive maintenance preserves cam and follower surfaces, sustains performance, and avoids costly top-end repairs.

Performance Terms That Define a Cam

Several specifications describe how a camshaft will influence engine behavior, guiding both OEM calibration and aftermarket tuning.

• Lift: Maximum valve opening; higher lift generally increases airflow but stresses springs and followers.
• Duration: How long a valve stays open (in crank degrees); more duration often shifts power higher in the rev range.
• Lobe separation angle (LSA): Angle between intake and exhaust lobe centers; tighter LSA increases overlap and mid/high‑rpm power but can roughen idle.
• Overlap: Period when intake and exhaust valves are open together; enhances scavenging at high rpm but can dilute idle quality and emissions at low rpm.

Manufacturers balance these parameters—and increasingly vary them dynamically—to deliver broad, usable performance with acceptable emissions and refinement.

Summary

The camshaft’s purpose is to time and actuate the intake and exhaust valves so the engine breathes correctly in sync with piston motion. Its design, placement, and control strategies determine how an engine idles, accelerates, saves fuel, and meets emissions standards. From fixed profiles to advanced variable systems, the camshaft remains the central coordinator of combustion airflow in modern internal combustion engines.

Is replacing a camshaft a big job?

Time and effort: Depending on the make and model of your vehicle, replacing a camshaft can be a time-consuming task. It may require several hours of work, including disassembly, inspection, replacement, and reassembly. Additionally, it may require special tools and equipment to complete the job properly.

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

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. 

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.