What is the function of the camshaft?

The camshaft’s function is to open and close an engine’s intake and exhaust valves at precisely timed intervals relative to the crankshaft, controlling how air enters and exhaust leaves the combustion chamber. In a four-stroke engine, the camshaft typically rotates at half the crankshaft’s speed, and its lobe shape and timing determine valve lift, duration, and overlap—key factors that shape power, torque, efficiency, and emissions.

How the camshaft works

A camshaft is a rotating shaft with egg-shaped lobes that push on lifters, rockers, or followers to open valves against spring pressure; when the lobe rotates away, springs close the valves. This coordinated motion times the intake of the air-fuel mixture and the expulsion of exhaust gases, ensuring each cylinder breathes optimally across the engine’s operating range.

Valve timing, lift, and duration

Valve timing is when a valve opens and closes in relation to crankshaft position. Lift is how far the valve opens; duration is how long it stays open. Overlap—the period when intake and exhaust valves are open together—helps scavenging at higher RPMs. These parameters, defined by the camshaft, are central to engine character: more lift and duration can boost high-RPM power, while milder profiles favor low-speed torque, drivability, and emissions.

Where it sits and how it’s driven

In pushrod/overhead-valve (OHV) engines, the camshaft is in the block, operating valves via lifters, pushrods, and rocker arms. In single or dual overhead cam (SOHC/DOHC) designs, camshafts sit in the cylinder head(s) and act directly on the valves or via short followers. Camshafts are driven by a timing belt, chain, or gears; accurate synchronization with the crankshaft is critical to avoid valve-to-piston contact in many interference engines.

Modern enhancements: Variable valve timing and lift

To balance performance and efficiency across a wide RPM range, many engines use systems that alter cam phasing (when lobes act) and, in some cases, valve lift and duration. These technologies improve torque spread, reduce fuel consumption, and cut emissions without sacrificing top-end power.

The following are common variable systems and what they adjust during operation:

• Cam phasing (e.g., Toyota VVT-i, Ford Ti-VCT, BMW VANOS): hydraulically rotates the camshaft relative to the sprocket to advance/retard timing.
• Variable lift/duration (e.g., Honda VTEC, BMW Valvetronic, Nissan VVL): switches or continuously varies rocker geometry to change lift and/or duration.
• Electro-hydraulic valve control (e.g., Fiat MultiAir): uses oil control to modulate intake valve events more independently of the cam lobe, reducing throttling losses.

Together, these systems let the engine “retime” its breathing on the fly, optimizing response at low RPM while sustaining airflow at high RPM for stronger output.

Why it matters to performance and efficiency

Because the camshaft governs the engine’s breathing, it directly shapes drivability and economy. Engineers and tuners choose cam profiles that match the vehicle’s mission, whether that’s smooth urban efficiency or high-rev track performance.

Below are key outcomes influenced by camshaft design and control:

• Torque curve: Earlier intake opening and conservative overlap aid low-end torque; aggressive profiles shift torque higher in the rev band.
• Peak power: Higher lift and longer duration increase high-RPM airflow, raising top-end power when paired with appropriate intake/exhaust flow.
• Idle quality and NVH: Mild cams idle smoothly; long-overlap cams can lope and run richer at idle.
• Fuel economy: Optimized timing reduces pumping losses; variable systems trim fuel use in real-world driving.
• Emissions: Precise timing cuts unburned hydrocarbons and NOx by improving combustion and enabling catalyst-friendly exhaust conditions.
• Turbocharging synergy: Cam timing tailored for boost improves spool, reduces reversion, and stabilizes combustion under pressure.

In practice, modern engines balance these trade-offs with variable systems, delivering both tractable low-RPM behavior and strong high-RPM performance.

Additional roles and considerations

Beyond actuating valves, camshafts can drive or coordinate with other engine systems and require proper lubrication and alignment to prevent wear. Their health is monitored electronically to maintain precise timing.

Here are notable secondary roles and maintenance factors:

• Ancillary drives: Older engines use the camshaft to drive a distributor or mechanical fuel pump; some diesels use cam lobes to actuate unit injectors.
• Sensors: A camshaft position sensor feeds the ECU for sequential fuel injection and ignition timing, working with the crank sensor.
• Materials and followers: Camshafts are typically chilled cast iron or billet steel; followers may be flat tappet or roller. Mismatch or poor oiling can cause lobe wear.
• Valve lash: Hydraulic lash adjusters self-compensate; solid-lifter setups need periodic adjustment to maintain precise events.
• Timing service: Belts need interval-based replacement; chains need good oil quality and may eventually need guides/tensioners. Slipped timing risks engine damage in interference designs.
• Symptoms of issues: Misfires, rough idle, loss of power, metal in oil, or timing-related fault codes can point to cam wear or phaser/drive problems.

Managing these factors preserves accurate valve events, which protects performance and engine longevity.

What engines don’t use camshafts?

Most two-stroke engines don’t need a camshaft because ports in the cylinder wall control gas exchange. Experimental and niche “camless” designs use electromagnetic or electro-hydraulic actuators (e.g., Koenigsegg’s Freevalve) to control valves independently, but widespread production remains limited; the conventional camshaft with variable control is still the norm in 2025.

Summary

The camshaft’s core function is to time and actuate the intake and exhaust valves so the engine breathes correctly. By defining valve lift, duration, and timing—and, in modern engines, varying them dynamically—the camshaft determines the balance of torque, power, efficiency, emissions, and drivability across the rev range.

What is the main function of the cam shaft?

Camshafts are integral components of internal combustion engines, responsible for controlling the opening and closing of the engine’s intake and exhaust valves. As the camshaft rotates, its lobes push against the valves, allowing the intake of air and fuel and the expulsion of exhaust gases.

Does the camshaft move the lifters?

Each lifter is free to move up and down in the bore as it follows the con-tour of the rotating cam lobe. The pushrod then transfers this up-and-down motion to the rocker arm. This is the bottom-side, or cylinderside view of the combustion chamber, which is the side the valves are installed from.

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