This article explains what takes place when a car engine knocks and the various causes of engine knocking sound.
How does the engine knock occur?
In internal combustion engines, only the spark plug is meant to ignite the fuel-air charge, and this should occur at a precise point in the piston’s stroke cycle. Knocking occurs if the combustion does not take place at the optimum moment in the cycle.
Normally, each of the engine cylinders should have the right balance of fuel and air. This enables the fuel to burn in small, controlled pockets. However, when the fuel burns unevenly, the sparks go off at random times, giving rise to a knocking sound in the engine. If the knocking sound starts suddenly while you are on the road and it gets progressively worse, you may require a mobile mechanic to diagnose and possibly fix the problem immediately.
Causes of engine knock
- Low octane fuel
In general, the higher the octane rating of a fuel, the more compression it can withstand before it ignites. High octane fuel tends to be more expensive, but they burn more uniformly and resist knock. Long-term use of fuel with an octane rating that is lower than your car manufacturer’s recommended fuel type can damage your car engine.
- Accumulation of carbon deposits
When carbon deposits accumulate inside the cylinder, they occupy space and reduce available space for fuel and air. This generates increased pressure within the cylinder, leading to ill-timed sparks that can give rise to knocking sounds. Reduced performance of the engine due to the build-up of carbon deposits may also result in overheating. It is advisable to have your engine checked for accumulation of carbon deposits by trained car service technicians at regular intervals.
- Faulty spark plugs
Spark plugs are required to ignite the fuel-air charge in the cylinder. Over time, spark plugs age and break down, causing them to malfunction and leading to knocking sounds. Ageing or faulty spark plugs should be replaced at regular car tune-up services.
- Worn bearings
The pistons move up and down within the engine cylinder, turning the crankshaft, which powers the movement of the car. The pistons require rod bearings to facilitate the smoothness of their movement. As the rod bearings begin to wear, they may come out of their positions, letting the pistons rattle against the crankshaft and creating the knocking sound. This type of problem often requires major repairs of the engine and should only be undertaken by experienced mechanics. New bearings would be required, and pistons or the crankshaft may need repairs or replacement.
- Faulty knock sensor
The engine requires the right mixture of air and fuel to function optimally. If the air-fuel mixture is lean, it means the cylinder does not have enough fuel but has too much air and this mixture won’t burn fast enough. This can lead to multiple firing, giving rise to knocking sounds. Fortunately, modern cars are now fitted with knock sensors designed to detect engine knock early and send appropriate signals to the engine control unit so that the problem can be corrected automatically. If the knock sensor is faulty, this mechanism will not be activated and knocking may persist until the engine becomes damaged. If you drive a car with this enhancement, it is advisable to have your knock sensor checked whenever you take your car for a tune-up service.
Get in touch with a mechanic near me
Engine knock can damage the cylinder walls and pistons of your car engine if not fixed on time. How to fix engine knocking depends on the cause, and this is stated under each of the causes of knocking explained above. Contact the car repair near me today at Beachwheels Automotive to book a service or undertake heavy vehicle repairs.