What is the purpose of a camshaft?

A camshaft opens and closes an engine’s intake and exhaust valves at precisely timed moments, converting the crankshaft’s rotation into the valve motions that let an internal-combustion engine breathe. By controlling when and how far valves move, it dictates power, fuel efficiency, emissions, idle quality, and drivability.

Core role in an engine

At its simplest, the camshaft is the engine’s mechanical conductor: its lobes press on followers, lifters, or rocker arms to open valves, while springs close them. The camshaft is synchronized to the crankshaft via a timing belt, chain, or gears so these “valve events” occur at the correct points in the four-stroke cycle (intake, compression, power, exhaust). The following points summarize what a camshaft actually does and why it matters.

• Times and actuates valves: Cam lobes translate rotation into lift, opening intake and exhaust valves with precise timing and duration.
• Synchronizes with the crankshaft: In a four-stroke engine, the camshaft rotates at half crank speed to align valve events with piston position.
• Shapes engine character: Cam profile (lift, duration, overlap) determines torque curve, peak power RPM, throttle response, and idle smoothness.
• Influences efficiency and emissions: Timing affects cylinder filling and scavenging, internal EGR via overlap, and catalytic converter light-off.
• Interfaces with ancillary systems: Historically, the camshaft drove distributors and mechanical fuel pumps; today it often drives high-pressure fuel pumps in direct-injection engines.
• Prevents mechanical failure: Proper profiles and springs avoid valve float at high RPM and keep valves from contacting pistons in interference engines—provided timing stays correct.

Together, these functions make the camshaft central to how an engine breathes and, ultimately, how it performs and lasts.

How a camshaft works

From rotation to valve motion

Each cam lobe is an eccentric shape designed to lift a follower or lifter, transferring motion through a pushrod and rocker (in overhead-valve/pushrod engines) or directly to the valve via a rocker/finger follower (in overhead-cam engines). Valve springs return the valve to its seat as the lobe rotates away. Dual overhead cam (DOHC) layouts typically dedicate one cam to intake valves and one to exhaust, allowing finer control at high RPM.

Timing relationship with the crankshaft

Precision timing is essential. In four-stroke engines, the camshaft turns at half the crankshaft’s speed so that each valve opens once every two crank revolutions. Timing belts, chains, or gears maintain this relationship; if timing slips, performance suffers or, in interference engines, the pistons can strike open valves. Many two-stroke engines use ports instead of poppet valves and have no camshaft, although some two-stroke diesels use camshafts to operate exhaust valves.

Camshaft specifications and their effects

Engine behavior is heavily influenced by a few key camshaft parameters. Understanding them explains why one engine idles smoothly and another screams at high RPM.

1. Lift: How far the valve opens. Higher lift increases airflow and potential power but can stress valvetrain components and require stronger springs.
2. Duration: How long the valve stays open, measured in crankshaft degrees. Longer duration favors high-RPM power but can reduce low-end torque and idle quality.
3. Lobe separation angle (LSA) and overlap: The angular distance between intake and exhaust lobe centers; tighter LSA increases valve overlap, improving scavenging at high RPM but raising emissions and roughening idle.
4. Ramp rates: How quickly the lobe lifts the valve. Faster ramps improve area under the lift curve (airflow) but can increase wear and risk of valve float if springs aren’t matched.

The art of cam design is balancing these traits for the intended use—quiet, efficient commuting, broad-shouldered towing torque, or peak track performance.

Modern advancements

Contemporary engines use advanced systems to make camshafts more adaptable, broadening powerbands and cutting fuel use and emissions without sacrificing drivability.

• Variable valve timing (VVT): Cam phasers hydraulically or electrically advance/retard cam timing on the fly (e.g., VVT-i, VTC, VANOS), optimizing valve events for low-end torque, high-RPM power, and reduced emissions.
• Variable valve lift/dual-profile systems: Mechanisms like VTEC, Valvetronic, and MultiAir alter lift and/or duration to reduce pumping losses at low load and unlock airflow at high load.
• Cylinder deactivation: Special lifters collapse to keep some valves closed under light load, improving efficiency while the cam still operates the remaining cylinders.
• Direct injection integration: Many modern gasoline engines drive a high-pressure fuel pump from an extra cam lobe, precisely orchestrating fuel delivery.
• Alternatives and outliers: Ducati’s desmodromic systems use cam-driven closing instead of springs; emerging “camless” concepts (electromagnetic/hydraulic actuators, such as Koenigsegg’s Freevalve) exist but are not yet mainstream.

These technologies let a single engine behave like several—quiet and efficient in traffic, responsive on demand, and clean enough to meet stringent standards.

Beyond cars and trucks

While camshafts are synonymous with automotive engines, the underlying cam principle is common in machinery—from textile equipment to packaging lines—where precise, repeatable motion is required. In pure battery-electric vehicles, which lack combustion engines, camshafts aren’t used at all; in hybrids, they remain central to the ICE portion.

Common questions

Do electric vehicles have camshafts?

Pure EVs do not, because they use electric motors rather than combustion engines. Hybrids still rely on camshafts in their internal-combustion engines, often with VVT and variable lift.

What maintenance keeps camshafts healthy?

The camshaft itself is robust, but its performance depends on lubrication, correct timing, and clean oil. Watch for the signs and service items below.

• Symptoms of trouble: Ticking/knocking from the valvetrain, misfires, loss of power, metal in oil—possible lobe or follower wear or timing issues.
• Timing components: Replace belts, chains, tensioners, and guides on schedule; a skipped tooth can cause severe engine damage in interference designs.
• Oil quality: Follow the correct grade and interval; modern variable systems rely on clean oil to actuate cam phasers and lifters.
• Sensors and solenoids: Faulty VVT solenoids or cam sensors can upset timing control and trigger check-engine lights.

Proactive maintenance preserves timing accuracy and reduces wear, safeguarding both performance and engine longevity.

Summary

The purpose of a camshaft is to open and close engine valves with exact timing, translating crank rotation into the valve motions that control an engine’s breathing. Through its profile and timing—and increasingly with variable systems—it determines how an engine idles, pulls, revs, sips fuel, and meets emissions targets. In short, the camshaft is the choreography behind every combustion event.

What is the main function of a camshaft?

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 a camshaft increase horsepower?

A camshaft can compensate for other limiting factors in your engine like a poor exhaust port design, where a little additional cam timing on the exhaust will help. And, as evidenced by this cam test, a “still streetable” cam can provide a power increase in excess of 100 horsepower.

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 the camshaft goes bad?

A faulty camshaft can cause misfires by disrupting the timing of the valves. If the camshaft lobes are worn or damaged, they may not open the valves correctly, leading to incomplete combustion in the cylinders. This improper combustion results in misfires and can cause further damage to your engine.