What is Piston Slap? Causes, Symptoms, and Solutions.

Piston slap refers to the annoying sound came out from the engine side. In this article, I will briefly discuss the piston slap symptoms and a full guide for your better knowledge. 

Piston Slap

Piston Slap

The engine is the main component of a vehicle. The piston is also a very crucial component inside the engine. So, the repair and maintenance of the piston is very important. 
Piston slap refers to the knocking or tapping sound coming from the engine compartment. Piston slap is a commonly encountered issue in internal combustion engines that can lead to unwanted noise, reduced performance, and potential long-term damage if left unaddressed.
Piston slap refers to the knocking or rattling noise produced when the piston moves inside the cylinder bore. This happens due to excessive clearance between the piston and the cylinder walls.
The piston, which is designed to fit snugly within the cylinder, experiences a slight sideways movement during its reciprocating motion. When the gap between the piston and the cylinder becomes excessive, it leads to unwanted piston slap noise.

Causes of Piston Slap

The engine piston wants to move frequently inside the cylinder bore. The lubrication inside the cylinder bore helps to move it freely inside. If there is any problem that happens inside it will cause noise. 
Various factors can contribute to the development of piston slaps in an engine. Some common causes include:

worn cylinder walls

Over time, the cylinder walls can wear out, resulting in an increased gap between the piston and the cylinder. The cylinder wall has a thin aluminum alloy-coated liner, which helps the piston move freely inside the cylinder bore. If the cylinder gets clogged then the movement of the piston can hamper. The clearance also can get increased. This increased clearance leads to piston slap.

Improper Piston Design

Inadequate piston design, such as incorrect skirt shape or insufficient skirt coating, can contribute to increased piston-to-cylinder clearance and subsequently cause piston slap. 

Incorrect Piston Installment

If the piston is not installed correctly, it can lead to misalignment and increased clearance, leading to piston slap. The proper skilled and trained technicians can fix the piston to its own place. So it is very important to check the engine from time to time with proper guidance.

Improper Lubricant

If the quality and the quantity of the lubricant are not sufficient, then it could not build an oil film between two rubbing parts. Here the piston and cylinder wall rub with each other, if better lubrication does not happen then the friction will increase and the cylinder liners can get clogged. For that reason, the piston and the cylinder walls can make noise. This could be a piston slap. 

Worn-out Piston Rings

The piston has commonly 3 types of rings- two compression rings, and one oil scrapper ring. If the piston ring gets clogged then the combustion thrust can give extra pressure on the piston head, causing the piston to slap. 
The above reason can damage the engine also. If there are such problems happen then it is advisable to replace the damaged parts with the new ones. 

Symptoms of Piston Slap

Detecting piston slaps early on is crucial for preventing further damage to the engine. Some common symptoms of piston slap include:

Knocking Noise

The most evident symptom of piston slap is a knocking or rattling noise, particularly during cold starts or when the engine is under load. The tick-tick sound will come out from the engine side. It causes engine safety also.

Decreased Performance

Piston slap can result in reduced engine performance, including decreased power output and acceleration. When the driver gives the full acceleration at that time the power output is not sufficient. When the car load is higher than the specific marking then this type of problem can happen. 

Increased Oil Consumption

Excessive piston-to-cylinder clearance can cause increased oil consumption as oil bypasses the piston rings and enters the combustion chamber. 

Black Smoke

If black smoke comes out from the exhaust system, this can happen with the burning of engine oil in the compression stroke. If this happens that means the oil ring is clogged and need to be replaced. 

Solutions for Piston Slap

If you suspect that your engine is experiencing a piston slap, it’s important to take appropriate measures to address the issue promptly. Here are some solutions that can help mitigate piston slap:

Engine Warm Up

Allowing the engine to warm up properly before driving at higher speeds can help reduce piston slap noise. If the engine is not at working temperature then the knocking sound can happen. 

Regular Maintainance

Regularly servicing your engine, including oil changes, can help maintain optimal performance and reduce the likelihood of piston slap.

Piston Replacement

In severe cases of piston slap, where the piston and cylinder clearance is beyond acceptable limits, replacing the piston with a correctly sized one can effectively eliminate the issue.

Cylinder Boring

If the cylinder walls are worn or damaged, professional honing or boring can restore the correct dimensions and reduce piston slap.


Piston slaps occur in internal combustion engines and lead to unwanted noise and potential engine damage. By understanding the causes, recognizing the symptoms, and implementing appropriate solutions, you can effectively mitigate the effects of piston slap and ensure the optimal performance and longevity of your engine.
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