What does engine knocking mean?

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 There is no doubt that hearing a knocking sound from your engine is terrifying. It indicates serious and expensive problems that need to be attended to immediately.

Engine knocking occurs when the furl and air mixture in the vehicle’s cylinder are not functioning well causing the fuel to burn unevenly. Usually when the engine is working properly, the fuel burns evenly in little pockets.

When these pockets start to burn unevenly for whatever reason, a shock wave occurs producing a knocking sound in the engine. This sound indicates serious problems to the engine pistons and the cylinder walls.

Causes of engine knocking

There are five most common reasons for engine knocking in car engines. They include the following.

Imbalanced fuel and air ratios:

There should be a balanced ratio of air and fuel in the combustion chamber in the engine. If this proper balance of ratios is altered, it causes the fuel to burn unevenly.

If not repaired immediately and the knocking continues, the cylinder suffers extensive damage to its walls and damages other surrounding components. Replace these parts as soon as possible to prevent further damage.

Low octane rating:

Different fuels have different octane rating. This rating is indicated on fuel pumps at gas stations. The rating refers to how prone the fuel is to engine knocking as it is being compressed in the combustion chamber.

High performance cars use fuel with higher octane rating than regular cars, above 90. If the octane rating is too low, the fuel-air mix will ignite too soon causing a knocking sound to be produced.

Using spark plugs that are not compatible:

Different spark plugs have different resistance to hot temperatures. Using a spark plug that cannot handle your engine’s heat causes the engine to knock.

Carbon deposits:

Carbon particles form when the fuel-air mix is ignited. There should therefore be a cleaning detergent to eliminate these carbon molecules. If there is none, carbon deposits mess with the combustion process and cause the engine to knock.

Unlubricated cylinders:

Cylinders have to be well lubricated throughout. If they lack lubrication, loose filters and valves become dry and cause a knocking sound to be produced in the engine. Always check to ensure that there is proper flow of oil around the cylinder head. If there is an oil leak or the oil is oil and dirty, replace with new oil immediately.

Rod knock:

The rod is the part that connects the pistons and crankshafts. A rod knock is a problem that occurs when the bearing that connect the rod and the shaft fail. This produces a knocking or tapping sound from the engine.

In more serious cases, the rod itself knocks against the crank shaft. The noise gradually reduces as you accelerate and when the temperature is very cold but gets louder when there isn’t enough fuel in the tank. Oil knock is caused by a number of reasons including:

  1. Oil that isn’t sufficiently viscous
  2. Low oil pressure
  3. High oil temperature
  4. Excess revving
  5. Excess inertia force on the pistons
  6. You can fix a rod knock problem by following the steps below:
  7. Drain the oil out
  8. Replace the oil filter with a new one. Install and close tightly using wrench
  9. Put in new fresh oil, about five quarts. Check the rod bearings while at it and ensure they are shut tightly
  10. Clean the fuel injector to prevent debris from getting into the engine.

Faulty spark plugs:

Bad plugs means the plugs are either loose or cracked or both. If you hear a knocking noise coming from the engine, make sure to visually inspect the plugs. Pull them out and examine them for cracks.

Also check whether they are loosely connected in the first place by wiggling them to see if they move. Replace a knocking y bad spark plugs to fix this problem.

Exhaust Leak:

An exhaust manifold leak causes ticking when the engine is idle or accelerating. It occurs when exhaust gases leak from the gaskets at high pressure. It is not a serious problem and you can still drive around with it but should be fixed quickly enough so it does not develop into a worse and expensive issue.

How to fix engine knocking

Once you experience an engine knock, you can fix them in the following ways:

  • Use a carbon cleaning detergent: These detergents clean the carbon deposits that form in the cylinder when the fuel and air mixture combusts. The deposits are responsible for any knocking sound in the engine. Ask your mechanic the most suitable detergent for your car.
  • Check octane levels: As we’ve seen above, low fuel octane levels cause engine knocks. Check the levels at a gas station before gassing up.
  • Replace bad spark plugs.

Other problems related to engine knocking

The following are some of the causes of engine knocking:

Low oil Level:

If you do not fix this problem soon enough, other components such as the valve trains, rockers, and camshafts develop serious issues. Check oil levels regularly, like once a month, using a dipstick to ensure you have enough.

Check oil pressure with special gauges designed for this purpose. Recommended pressure is between 15 and 20 PSI. Also remember that oil should be checked when the engine is warm at idle.

Valves without adjustment:

This is a very common cause of knocking noise. The valves work by opening and closing once per tow engine spins. As they work, normal wear occurs that causes the valves to fall out of line and variable distances between each other.

This produces a knocking noise as the valves move around when the engine is running. The silver lining to this problem is that it is the easiest and cheapest to fix.

You can fix the problem by replacing the old shims with new ones and adjusting the rocker arms. If you have a pushrod engine, ensure the lifters are clean as oil deposits tend to accumulate on them over time causing the knocking noise.

Rod knock:

The rod is the part that connects the pistons and crankshafts. A rod knock is a problem that occurs when the bearing that connect the rod and the shaft fail. This produces a knocking or tapping sound from the engine.

In more serious cases, the rod itself knocks against the crank shaft. The noise gradually reduces as you accelerate and when the temperature is very cold but gets louder when there isn’t enough fuel in the tank.

Faulty spark plugs:

Bad plugs means the plugs are either loose or cracked or both. If you hear a knocking noise coming from the engine, make sure to visually inspect the plugs. Pull them out and examine them for cracks.

Also check whether they are loosely connected in the first place by wiggling them to see if they move. Replace any bad spark plugs to fix this problem.

Wear and tear:

There are a lot of components that make up the engine. Some of them include: pistons, valves, shafts and pushrods. If any of these components experience wear and tear, you will hear ticking a tapping noise in your engine.

To prevent further damage, ensure you replace the components fast or they might develop into clunking noises which are known to be much more serious.

Conclusion

Engine knocking is a serious issue that needs to be checked immediately. If left for too long, they can cause further damage that might ruin your car permanently.

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Steven Reilly
Steven Reilly is a qualified mechanic and his passion for cars goes beyond just the technical aspects. He is also an amateur racer and all round car enthusiast. When he is not driving them, he can often be found in his garage under the hood of a rare model. Steven Reilly has lost track of the number of hours he has spent setting up his fine collection of rebuilt models. He believes that cars can provide a constructive and fun opportunity to teach the youth important life skills. In line with this, he is developing a community outreach program, potentially dubbed ‘Cars for change'.

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