What makes a camshaft move

The camshaft is moved by the engine’s crankshaft through a timing belt, timing chain, or gear train; in a four‑stroke engine it turns at half the crankshaft speed, and variable valve timing devices can shift its phase but do not power it. Put simply, torque originates at the crankshaft—first from the starter motor during cranking and then from combustion—and is transmitted to the camshaft through a synchronized drive so valves open and close at precise moments.

The mechanical drive: how the crankshaft turns the camshaft

In conventional piston engines with camshafts, the crankshaft is the prime mover. As the crank spins, it drives the camshaft via a positive, synchronized link—belt, chain, or gears—so valve events stay in time with piston motion. In four‑stroke engines the camshaft rotates at a 2:1 reduction (one cam revolution for every two crank revolutions). In cam‑in‑block (OHV/pushrod) engines a single cam drives lifters and pushrods; in OHC/DOHC layouts, one or more overhead cams are driven at the top of the engine. Tensioners, guides, and sprockets maintain alignment and manage vibration, while engine oil reduces friction at cam journals and lobes.

Timing belt drives

Synchronous toothed belts are quiet and light, commonly used in many passenger cars. They rely on precise tooth engagement to keep timing, assisted by spring or hydraulic tensioners and idler pulleys. Belts are typically dry and require periodic replacement per the manufacturer’s interval; failure on interference engines can cause valve-to-piston contact.

Timing chain drives

Roller or “silent” chains run in oil and are guided by plastic or metal rails with hydraulic tensioners that use oil pressure to keep the chain taut. Chains are durable and often intended to last the life of the engine, though wear, guide degradation, or tensioner issues can stretch timing, trigger rattle, or illuminate fault codes.

Gear trains

Direct gear drives—common in heavy‑duty diesels and some performance engines—use meshing gears (often with idlers) for highly precise timing and robust durability. They add cost, weight, and potential gear lash noise, but excel in environments demanding reliability under high loads.

What turns it first: starting, idling, and running

At start‑up, the camshaft moves because the starter motor spins the crankshaft via the flywheel or flexplate; the timing drive simply follows. In stop‑start and many hybrids, an integrated starter‑generator or the traction motor performs this cranking role. Once the engine fires, combustion torque at the crank continues to drive the camshaft. Across all operating modes, the cam’s motion is always a consequence of crankshaft torque transmitted through the timing system.

Variable valve timing: adjusting when, not powering how

Modern engines use variable valve timing (VVT) and sometimes variable lift systems to broaden torque, improve efficiency, and cut emissions. Cam phasers mounted on the cam sprocket advance or retard cam angle relative to the crank, using engine oil pressure or electric motors. These devices do not generate the rotation that moves the camshaft; they fine‑tune its phase while the crankshaft provides the motive power.

The following list outlines the main types of cam phasers and how they modify cam timing.

• Hydraulic vane phasers: Oil pressure rotates an internal vane within a housing to advance/retard angle (e.g., Toyota VVT‑i, GM VVT, many Ford and Hyundai/Kia systems).
• Helical/screw phasers: Oil‑actuated axial movement through helical gears produces a rotational phase shift (e.g., earlier BMW VANOS generations).
• Electric cam phasers: A compact e‑motor adjusts phase directly or assists hydraulics for faster, low‑temperature response (e.g., Toyota VVT‑iE on intake cams, various Delphi/Bosch eVCT systems).

Regardless of type, phasers are adjusters, not drivers: they trim the cam’s position while the crank-and-timing drive supply the rotation.

What resists cam motion: loads, lubrication, and dynamics

While the crank drives the cam, several forces resist and shape that motion. Valve springs press on cam lobes through followers (buckets, lifters, or rockers), creating cyclic loads. Oil reduces friction at journals and lobes; inadequate lubrication can increase drag or cause wear. The timing system must also absorb torsional vibrations and transient shocks from changing cylinder pressures and rapid throttle events, which is why you’ll find chain guides, damped tensioners, and phaser lock pins to stabilize timing at idle and during starts.

Configurations and exceptions

Most four‑stroke gasoline and diesel engines use camshafts and the 2:1 crank-to-cam speed relationship. Two‑stroke gasoline engines typically omit camshafts altogether, using ports instead of valves, while some two‑stroke diesels employ gear‑driven cams for valves or unit injectors. A small but notable exception is “camless” technology—such as Koenigsegg’s Freevalve—where electronically controlled pneumatic‑hydraulic actuators replace cams. In those designs, there is no camshaft to move; valve events are commanded directly.

Key parts that transmit motion to the camshaft

To understand the motion path at a glance, it helps to identify the core components that take torque from the crankshaft and deliver it to the camshaft.

• Crankshaft: The original source of rotation, driven by the starter motor and then combustion.
• Timing element: Belt, chain, or gears that maintain synchronized motion between crank and cam.
• Tensioners and guides: Keep the belt/chain tight and damp vibration to preserve precise timing.
• Cam phaser (if equipped): Adjusts the cam’s phase angle relative to the sprocket but does not power rotation.
• Camshaft bearings and followers: Support rotation and transfer lobe motion to valves with minimal friction.

Together, these parts ensure the camshaft turns reliably, stays in time with the pistons, and can be finely adjusted for performance and efficiency.

Summary

A camshaft moves because the crankshaft drives it through a synchronized timing system—belt, chain, or gears—with a 2:1 speed ratio in four‑stroke engines. Starter motors (or hybrid e‑machines) spin the crank first; combustion sustains rotation thereafter. Variable valve timing phasers can advance or retard cam timing but do not power the cam. Proper tension, lubrication, and vibration control keep the motion precise so valves open and close exactly when they should.

How to tell if a camshaft is bad?

You can tell a camshaft is bad through performance issues like a rough idle, engine misfires, and loss of power, noticeable noises such as loud ticking or tapping, and warning signs like a check engine light and metal shavings in the oil. Other symptoms can include poor fuel economy, difficulty starting the vehicle, and backfiring. 
Common Symptoms of a Bad Camshaft

• Engine Performance Issues:
  • Loss of Power: You’ll feel reduced engine power and poor acceleration. 
  • Rough Idle: The engine may sputter or run unevenly, especially when idling. 
  • Misfires: Inconsistent operation of the valves can lead to incomplete combustion, causing misfires. 
  • Stalling: The engine may stall, particularly at low speeds or when stopped. 
  • Hard Starts: A faulty camshaft can affect the timing of ignition, making the engine difficult to start. 
• Audible Clues:
  • Loud Ticking or Tapping: Worn camshaft lobes or bearings can create loud ticking or tapping noises from the engine’s upper cylinder area. 
  • Backfiring: Worn valves may not open or close correctly, causing unburnt fuel to ignite in the intake or exhaust system. 
• Warning Lights & Diagnostics:
  • Check Engine Light: A faulty camshaft can disrupt engine sensors, triggering the check engine light. A flashing light indicates a serious misfire. 
  • OBD2 Codes: Connect an OBD2 scanner to your vehicle to retrieve diagnostic trouble codes (DTCs) that pinpoint the specific engine problem. 
• Physical Evidence:
  • Metal Shavings in Oil: When camshaft components wear down, they can create metal debris that contaminates the engine oil. 

What to Do Next

1. Scan for Codes: Use an OBD2 scanner to read any stored fault codes. 
2. Inspect the Oil: Check the engine oil for any visible metal shavings. 
3. Listen for Noise: Pay attention to any ticking, tapping, or knocking sounds coming from the engine. 
4. Inspect the Camshaft (if possible): In some cases, you can remove the valve cover to visually inspect the camshaft for wear or damage. 

If you notice these signs, it’s crucial to have a mechanic diagnose the issue to prevent further severe engine damage. 
This video demonstrates how to inspect the camshaft for wear and damage: 56sPeter Finn the Car DoctorYouTube · May 15, 2014

How does the camshaft move?

The cam rotates. The nose of the cam B reaches the valve lifter. And the valve is fully open the closing flank C closes the valve gradually.

What spins your camshaft?

Which turns the pistons up and down the cam shaft only needs to turn once to complete one full cycle of opening and closing the valves. Now remember those bumps on the cam shaft. Those are the loes.

What drives the camshaft?

The camshaft in an internal combustion engine is driven by the crankshaft through a timing chain, timing belt, or gear set. This connection synchronizes the camshaft’s rotation, which is at half the speed of the crankshaft, to ensure the valves open and close at the precise moments needed for the four-stroke cycle of the engine.
 
How the Drive Works

1. Crankshaft Rotation: The crankshaft rotates as the pistons move up and down during the engine’s cycle. 
2. Synchronized Connection: A timing chain, timing belt, or meshing gears connect the crankshaft to the camshaft. 
3. Reduced Speed: Because a camshaft completes one full cycle of valve operation for every two revolutions of the crankshaft (one cycle for the engine), it spins at half the speed of the crankshaft. 
4. Valvetrain Operation: The spinning camshaft, with its egg-shaped lobes, pushes on the valvetrain, which opens and closes the intake and exhaust valves at the correct times in the combustion cycle.