Camshaft engine: functions, problems, and inspection

Camshaft engine: functions, problems, and inspection

The camshaft has been a key component of internal-combustion engines since the early 1900s, surviving and outliving many technological advancements in the automotive industry. It plays a critical role in managing the intake, compression, ignition and exhaust processes of the engine.

What is a camshaft? Why is it important?

A camshaft is a rotating shaft which runs along the cylinder bank, consisting of teardrop-shaped cams, bearings and bearing journals. Its primary function is to open and close the intake and exhaust cylinder valves at specific times for a specific duration while the engine is operating. Each cylinder row has its own camshaft and they are driven by the gears or timing chain in the crankshaft. The timing of the component directly influences the RPM range of the engine. The camshaft lift (valve lift) also affects the power output, as a higher lift allows more air to flow through the cylinders.

Types of camshaft drive mechanisms:

 The top three camshaft designs: 
  • Single overhead cam (SOHC) — One camshaft per cylinder bank. These mechanisms were particularly popular in the 60’s and 70’s. Advantages: they are reliable, cheap to maintain, and lightweight. Disadvantages: the engines are noisy, valve tuning is restricted, the RPM range is limited.
  • Dual overhead cam (DOHC) — Two camshafts per cylinder bank. Most modern vehicles use DOHC mechanisms. Advantages: these engines have a higher horsepower, are quieter, and allow car owners to separately tune the intake and exhaust valve timing, increasing efficiency. Disadvantages: they are more expensive, difficult to maintain, and heavier.
    Types of camshaft drive mechanisms: dual overhead cam (DOHC)
  • Overhead valve (OHV/pushrod) — Like OHC engines, the valves are located in the cylinder head, however, the camshaft is installed inside the engine block. They include long rods which reach up to the head to move the rocker arms and actuate the valves. Advantages: These mechanisms are often more compact, cheaper to produce, and some have a better low-end torque than OHC mechanisms. Disadvantages: less control over valve timing, limited number of valves per cylinder, and the valvetrain is heavier.

Material: These components are usually made from either steel or cast iron.

Camshaft position sensors

When looking at the functions of this component, the role of the camshaft sensors is essential. These sensors collect information on the precise position and rotational speed of the crankshaft and then transmit this information to the engine control unit (ECU) in real time. The ECU requires this information to regulate the timing of the ignition and fuel injection processes. They work in cooperation with the crankshaft sensors to provide a comprehensive overview of the engine operation systems. The ECU can also be altered to optimise these processes – this is known as ‘chip tuning’.

Symptoms of a broken position sensor

  • ! The “check engine” light is on
    Symptoms of a broken position sensor
  • ! Starting difficulties
  • ! Jerking and stalling
  • ! Shifting gear problems
  • ! Poor fuel efficiency

Causes of camshaft failure

Causes of camshaft failure

If your vehicle’s camshaft stops working properly, this could do serious damage to the engine and you may not even be able to start it. You may also hear abnormal or loud noises coming from under the bonnet.

 Here are 5 common causes of camshaft failure: 
  1. Insufficient lubrication/using the wrong lubricant. The camshaft and valve train components need lubrication in order to function properly, particularly cam lobes. Make sure to apply the correct moly paste or oil to the components, as recommended by the car manufacturer to prevent wear.
  2. Lobe wear. If the cam lobes are worn or flat, this results in reduced lift and the valves may not even open at all when the engine is running at a low rpm or idling. The engine may also start to backfire at high speeds.
  3. Incorrect break-in procedure. For example, if the engine is turned over excessively or left inactive for too long before the initial start up, this could cause damage. The engine rpm needs to be high enough during the break-in period.
  4. The valve spring pressure is too high or too low. Make sure to replace the springs on time and that the new springs match the vehicle’s specifications.
  5. Mechanical interference. Common mechanical issues include spring coil bind and insufficient clearance between the valves and pistons, as well as between the rocker arm slots and studs.
  6. Contaminated oil/poor oil quality. Car owners may consider changing the engine oil or using engine flush products to get rid of oil contaminants and sludge build up.

It is important to check the cam components thoroughly for wear, cracks and other signs of damage before determining how to repair the component. If the damage is extensive, it may be more practical to replace the whole camshaft.

How to check the camshaft and position sensors

 Camshaft: 
  • i Check the oil feed pipe for any blockages.
  • i Clean and inspect the cam bearings for scratches and wear.
  • i Clean and inspect the cam lobes for damage.
  • i Check the shaft for cracks.
  • i Measure the cam lift: you can do this using a digital caliper. Firstly, you’ll need to measure the diameter of the cam base circle. Next, you will need to measure the largest diameter, known as the base circle and lobe lift. You can then calculate the cam lift by subtracting the base circle diameter from the base and lobe lift value.
 Sensors: 
  • i Check for wire damage or loose wires.
  • i Check the sensor for signs of damage.
  • i Remove it and check the reluctor wheel for damage.
  • i Check the voltage and resistance using a multimeter – this method may vary depending on the type of CKP sensor (inductive or hall effect).

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