Knock-Knock: How pistons can result in engine noise

Knock-knock has been the start to many popular jokes. However, this is one engine noise that's no joking matter.

Although some engine noise is normal in everyday driving, continuous and abnormal noises need immediate attention.

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There are a few different things in an engine that can cause engine noise, and one of these happens to be bad pistons or piston rings. Pistons are located in the heart of the engine and most engines have four, six or eight pistons. The piston ring which is located around the piston head, keeps oil from getting into the combustion chamber on the upper side of the piston.

A worn or loose piston pin can create a metallic or double knocking sound. Piston slap is generally more of a hollow, knocking noise. Even though a slight amount of piston slap is normal in many engines, a continuous amount needs to be serviced.

When diagnosing a piston issue your local Goodyear Gemini technician will look for the following things:

• They will inspect both the top and bottom of the pistons for cracks and wear.

• They will also take a close look at piston skirt for wear, galling in the pin bores or uneven wear around the piston rings.

• They also check to see if there's oil on top of the piston itself.

Some symptoms you as a driver can look for are blue smoke being emitted out of the exhaust pipe. This would occur due to oil mixing with fuel and air in the combustion chamber, thus creating smoke out of the tailpipe. Even a small drop of oil is enough to cause smoke. This would also affect the oil level in your car, forcing you to top off the oil in between your scheduled oil changes. You will also see a decline in your engine's overall performance, and an abnormal engine knock.

To help your Gemini technician diagnose the problem try to note at what speeds the engine knock occurs, be able to describe the noise, as well as the color of any smoke if it is emitted.

For more information concerning pistons visit www.jepistons.com.