What Does a Camshaft Do?

The main function of a camshaft is to precisely open and close an engine’s intake and exhaust valves by converting its rotational motion into timed linear motion via cam lobes, synchronizing valve events with the crankshaft to manage airflow, combustion, power, efficiency, and emissions. In modern four-stroke engines it typically turns at half the crankshaft speed and, through lifters, pushrods, or rocker arms, actuates the valves according to the cam profile.

How a Camshaft Works

A camshaft is a shaft with egg-shaped lobes (cams). As the shaft rotates—driven by a timing belt, chain, or gears—the lobes press on followers (tappets/lifters), rocker arms, or pushrods, lifting valves off their seats against spring pressure. As the lobe rotates past its peak (lift), the valve closes. In overhead-cam (OHC/DOHC) engines the camshaft sits in the cylinder head and acts directly on followers; in overhead-valve (OHV/pushrod) engines it sits in the block and uses pushrods and rockers to reach the valves. The camshaft’s phase relationship to the crankshaft is critical; on four-stroke engines it is geared so that one cam revolution aligns with two crankshaft revolutions.

What the Camshaft Controls

These are the principal roles the camshaft plays in an internal-combustion engine’s operation and behavior.

• Valve timing: when each valve opens and closes relative to piston position (crank angle).
• Valve lift: how far the valve opens, controlling airflow into and out of the cylinder.
• Valve duration: how long the valve stays open, shaping the engine’s power band.
• Valve overlap: the period when intake and exhaust valves are briefly open together to improve scavenging.
• Synchronization with the crankshaft: keeps valve events in step with piston travel for efficient combustion.
• Ancillary drive (legacy): in many older engines, the camshaft also drives the distributor and/or a mechanical fuel pump.
• Combustion efficiency and emissions: by governing airflow and mixture motion, it affects fuel economy and tailpipe emissions.
• NVH and idle quality: aggressive profiles can boost peak power but often at the cost of rougher idle and more noise.

Together, these factors determine how an engine breathes across the rev range, directly influencing torque, peak horsepower, drivability, and emissions compliance.

Camshaft Configurations and Placement

Camshafts come in several layouts, each with trade-offs in performance, packaging, and complexity.

• SOHC (Single Overhead Cam): one camshaft per bank operates both intake and exhaust valves; simpler, compact.
• DOHC (Dual Overhead Cam): separate intake and exhaust cams per bank; enables optimal valve angles and easier variable timing/lift; common in modern multi-valve engines.
• OHV/Pushrod: a single camshaft in the engine block actuates valves via lifters and pushrods; compact height, strong low-end torque, widely used in American V8s.
• Desmodromic (rare, motorcycles): cams open and close valves mechanically without springs to control valve motion at high rpm.

While OHC designs dominate modern passenger cars for efficiency and high-rpm breathing, pushrod architectures remain competitive where packaging, durability, and low-end torque are priorities.

Modern Technologies That Modify Camshaft Behavior

To widen the performance envelope and meet efficiency and emissions targets, manufacturers add systems that vary camshaft action in real time.

• Variable Valve Timing (VVT): hydraulically or electrically “phases” the camshaft relative to the crankshaft to advance/retard timing (e.g., VVT-i, VANOS, VTC).
• Variable Valve Lift/Duration: switches cam lobes or continuously varies lift/duration for better low-load efficiency and high-load power (e.g., VTEC, Valvetronic, MultiAir).
• Cylinder Deactivation: works with cam profiles to disable valves on selected cylinders under light load to save fuel.
• Camshaft Position Sensing: a sensor reports cam position to the ECU for precise fuel injection and ignition timing.
• Camless/Actuator-Based Systems (rare): electronic or pneumatic-hydraulic actuators control valves individually without a camshaft (e.g., Koenigsegg Freevalve); still uncommon in mass-market cars.

These technologies allow engines to adapt valve events to driving conditions, improving torque at low rpm, power at high rpm, and fuel economy in between.

Maintenance and Symptoms of Camshaft Issues

Proper lubrication and correct timing are essential to camshaft longevity and accurate valve events.

• Maintenance: timely oil changes, correct oil grade/additives (especially for flat-tappet cams), and scheduled timing belt/chain service.
• Valve lash checks: required on some engines to maintain correct clearance and prevent accelerated wear.
• Symptoms of trouble: ticking/knocking noises, misfires, rough idle, loss of power, metal shavings in oil, cam/crank correlation fault codes (e.g., P0016–P0019), or VVT solenoid/actuator errors.

Addressing lubrication and timing-system issues early prevents lobe wear, follower failure, and potential catastrophic valve-to-piston contact.

Common Clarifications

These points help distinguish the camshaft’s role from other engine parts and concepts.

• The camshaft is not the crankshaft: the crank converts piston motion to rotation; the cam controls valves.
• On four-stroke engines, the camshaft generally rotates at half the crankshaft speed.
• The timing belt/chain synchronizes the cam and crank; it does not actuate valves by itself.
• Camshafts don’t inject fuel; however, some mechanical diesels use a cam to drive injection pumps.
• Two-stroke engines typically lack camshafts because ports, not poppet valves, handle gas exchange.

Understanding these distinctions can simplify diagnostics and prevent part-confusion when servicing engines.

Summary

A camshaft’s main job is to open and close the intake and exhaust valves at precisely the right moments, converting rotational motion into timed valve movement that governs how the engine breathes. By setting valve timing, lift, duration, and overlap—and increasingly by varying these in real time—camshafts shape torque, power, efficiency, drivability, and emissions across the rev range.

What is the main function of the camshaft?

Function. The camshaft is a mechanical component of an internal combustion engine. It opens and closes the inlet and exhaust valves of the engine at the right time, with the exact stroke and in a precisely defined sequence. The camshaft is driven by the crankshaft by way of gearwheels, a toothed belt or a timing chain.

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.

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