Car Engine

What Causes Piston Slap And What To Do?

Mike Cross
Updated Aug 10, 2021
What Causes Piston Slap

We depend on our motor vehicles every day to get us to work or to take care of your families. So, following routine care and maintenance is a must. Cars are expensive and designed with a well thought out engine.

Even though you take care of your car by falling scheduled care, there are times when you may have an issue with some part or the other. When this happens, it is crucial to figure out the cause and take the steps necessary to correct the issue.

Car engines are designed to use pistons. The pistons are actually very important in keeping your engine running efficiently and smoothly. However, from time to time you may notice that something is off. This could very well be your piston and it needs to be checked out right away.

What Causes Piston Slap
What Causes Piston Slap

What are pistons?

To better understand how important pistons are to your car’s engine, we need to understand what they actually are.

The piston is a cylinder that is located in the engine block and it moves up and down. Air and fuel combine together in the combustion chamber to cause the movement. The piston is attached to a wrist pin, which is then connected to a crankshaft. Because so much heat is generated in the combustion chamber, pistons have to be designed to withstand a lot of heat.

Most pistons today are made from aluminum alloy. This makes them extremely durable. However, they are still subject to wear and tear like any other vehicle component. Since pistons are part of the engine, it is imperative that you figure out the problem and have it fixed as soon as possible.


How do I know if my car is experiencing piston slap?

Most cars today will be designed with sensors to monitor the air and fuel ratio mix and they will also have knock sensors. These tools will alert you to potential problems. You may see that your check engine light is suddenly on.

It is also likely that one of the early signs of piston slap is a rattling or knocking sound coming from under the hood. You may also notice other signs of piston failure too. If you notice that your vehicle is losing power and not able to accelerate the way it should, there is misfiring or if there is oil burning, then your car is probably experiencing piston failure.

What does piston slap sound like?

Piston slap will sound exactly as the name implies. It will be a knocking or slapping sound coming from underneath the hood of your car.

Why does piston slap happen?

Piston slap happens when there is too much clearance between the piston and the wall. This is especially true if your engine block is made from aluminum.

If your car has a piston that experiences more cold clearance, then the piston will have more velocity and more thrust into the sides of the block.

What are some options for fixing piston slap?

If your vehicle has piston slap, the check engine light will turn on, you can find the error code when you using best obd2 scanner. And there are a few things you can try to correct it.

Most cars today are designed with a knock sensor. The knock sensor is responsible for monitoring the sensors and noting any variations in them. This information is then transmitted to the car’s ECU, or onboard computer center. The computer center can then adjust the ignition timing. This will help prevent any piston slapping.

You can also try using an offset pin to help control the noise. The offset pin works by adjusting the motion of the piston. This reduced force will help control the piston from hitting the cylinder bore.

Another easy fix for piston slap has to do with reducing the distance between the piston and the cylinder bore. Over time and thanks to wear and tear, the gap between the two can gradually become wider and wider. Sometimes you simply need to tighten the bore. This immediately reduces the distance and controls the slapping.

Is piston slap harmful to your car’s engine?

While piston slap is not an issue that needs to be fixed immediately, it does need to be checked out. The noise itself is not harmful to the engine. However, it is a sign that the pistons are banging against the ides of the cylinder walls. Eventually this will cause harm to your engine. It is a good idea to take your car to your local mechanic as soon as you notice piston slap.

What are some other signs of piston trouble?

If your timing belt is worn or having issues, that could be a cause of piston trouble. The timing belt is used to help facilitate the movement between the pistons and the valves. If your timing belt is worn out it should be replaced immediately before any further damage can occur.

A burned piston can also cause trouble for you. If your engine has a dirty fuel injector, it can cause a hole to be burned into the top of the piston. If you are using the  wrong spark plugs for your vehicle, this can also cause the piston to become burned. Opening the hood of your car should be enough to spot the problem.

Worn piston rings can also be a contributor of piston slap. When the piston rings wear out, they allow air to get into the space between the piston and the cylinder. It is also possible for oil to leak into the space as well. This will cause your car to have white or gray exhaust and you will need to add oil more frequently.

Final Thoughts

Pistons are an integral part of your car’s engine. It is crucial that they are in good shape and fitted properly so that your engine can run efficiently.

If you notice a rattling or knocking sound coming from under the hood, it is imperative to have it checked out as soon as possible. You want to have any possible failure fixed as soon as possible to prevent or minimize damage to your car’s engine.

Mike Cross
Life is too short to drive with stock audio

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