Piston


Piston

Nine out of ten vehicles today come with a certain number of cylinders, which is usually four or six. However, there are also eight- and ten-cylinder engines as well as more exotic and luxury twelve- and even sixteen-cylinder motors. 


Whether your engine has four or six cylinders, or even more, each cylinder features a cylindrical piece of metal, called a piston, which moves up and down forced by the combustion process. An air/fuel mixture blows up due to an ignition spark or extremely high pressure, causing a specific piston to go down, while another one in another cylinder goes up, compressing an air/fuel mixture in that cylinder. The up-and-down movements of the pistons are converted into the rotational motion of the crankshaft, which, in turn, spins a transmission shaft. 

A typical car piston is made of cast aluminum and features several spring-loaded rings housed in special grooves that go around the piston. Some of these rings serve to prevent combustion gases leaks, while the others scrape oil from the cylinder walls to prevent it from burning.

How can I know that my pistons fail?

Most pistons are manufactured to live a lifetime. However, improper service or problems caused by other failed engine parts may lead to malfunctioning pistons. If your pistons fail or wear out, you’ll notice the following issues:

Abnormal noises from the engine

As a rule, pistons do not fail all at once. They usually wear slowly, increasing the gap between cylinder walls and pistons. Once it becomes too big, you may hear an abnormal noise, called piston slap, especially when the engine is warmed up.

Blue smoke from the tailpipe and increased oil consumption

A worn-out piston and poor piston rings can’t provide efficient sealing, allowing some engine oil to mix with an air/fuel mixture and to be burned during the combustion process. As a result of its burning, you see blue smoke coming from the exhaust. You’ll also mention that the oil level reduces on a regular basis.

Lack of engine performance and power

While worn-out pistons do not cause a significant loss of power and performance, a cracked or damaged piston will affect the engine’s compression, resulting in poor performance and acceleration along with unstable engine operation. 

Your dashboard’s check engine light is on 

A failed piston will influence just about every aspect of your engine operation, including its performance, fuel and oil consumption, and emissions. Since all these parameters are monitored by the engine control unit, it will turn on the check engine light once any problem is detected.

Driving a vehicle with a faulty piston is one of the worst things you can do to your engine.  This may cause serious damage to the related cylinder, connecting rod, valves and the crankshaft. The best thing you can do to prevent further engine damage is to shut down the engine and get in touch with your mechanic.

Is a piston repairable?

The short answer is no. However, the fact that one of your pistons needs a replacement is nothing compared to the damage it may cause to the engine. If you want to determine the extent of the damage caused by a failed piston, several special tests need to be done. 

Compression test

This test will allow for checking compression leaks, which cause poor performance and power.

Test with a borescope

A borescope is inserted through each spark plug hole to see physical damage to the cylinders and the pistons.

Reading engine trouble codes

In some cases an engine control unit can identify the root of a problem, providing a relevant trouble code. 

Every engine repair process involves a lot of labor and time. Your mechanic will need to take the engine apart to access a damaged piston and inspect it to find out what caused its failure. If your bad piston has a hole burned from its top or it’s melted, this is usually caused by overheating. A cracked piston says about incorrect ignition timing, while a scored piston with a lot of dents and scratch marks should tell you about poor air filtration or crankcase ventilation. In some cases, a piston can be scuffed on its sides, which is a sign of poor oil lubrication inside the cylinder. The worst scenario is a shattered piston when it hits intake and exhaust valves, causing damage to itself and the valves at the same time. This usually happens because of a loose timing chain or belt, or a defective auto tensioner. 

The repair cost will vary depending on the damage caused by a bad piston. In some cases, an entire engine replacement or rebuild will be required. If your car is old and is not covered under the manufacturer’s warranty, you should make a decision whether it is worth repairing or it’s cheaper to purchase another car. On the other hand, if you own a new car and can afford to fix it, an engine replacement or rebuild is the way to go. 

Can I fix the problem myself?

A bad piston is synonymous with extensive engine damage which requires a special knowledge and tools to be fixed. Unless you’re a qualified mechanic, it’s better to leave this job to a professional. However, you can prevent damage caused by a failed piston by following the owner’s manual recommendations as well as oil, spark plugs and coolant change intervals.

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