learning about auto repair expenses

Why Do Worn Piston Rings Require An Engine Overhaul?

Piston rings are a part of your engine you probably don't spend much time thinking about it, and that's generally a very good thing. While these components are relatively inexpensive, they're located deep within your engine and require a substantial amount of time and effort to reach. Unfortunately, worn piston rings are often inevitable as any vehicle ages, and they can cause significant problems.

What Do Your Piston Rings Do?

You probably have a rough idea of how an internal engine work. Each cylinder in your engine contains a combustion chamber where all the action happens. This chamber has a moving piston at the bottom and the intake and exhaust valves at the top. The valves allow the fuel and air mixture to enter and exhaust gases to leave, while the piston should theoretically keep everything well sealed.

There's a problem with this setup, however. The piston needs to move up and down freely, which prevents it from forming a perfect seal against the cylinder walls. Sealing too well also creates extra friction, reducing engine efficiency and resulting in more wear on the cylinder walls. On the other hand, a poor seal creates blowby, burnt oil, and other severe issues.

Your piston rings help to create a compromise between these two extremes. Each piston has three rings that act as seals for the chamber. These rings can move somewhat freely, but they form tight seals as the piston moves up and down while your engine is at its standard operating temperature. The lower right also helps scrape oil from the cylinder walls, allowing it to re-enter the crankcase.

What Happens When Piston Rings Wear Out?

All piston rings allow some minuscule leakage, even when brand new. As the rings age, they wear down and seal more poorly. Poor maintenance can cause piston rings to degrade more rapidly as carbon buildup and sludge can wear them down or become trapped in the rings. Worn piston rings allow combustion products to enter the crankcase and oil to enter the combustion chamber.

Ultimately, these problems will burn oil and reduce compression inside your combustion chamber. Low compression will reduce your engine's efficiency and power and, if it becomes severe enough, cause misfires and prevent your engine from starting. Piston ring wear is irreversible, so once you notice the early symptoms, it's only a matter of time until they become more severe.

Unfortunately, repairing an engine with worn piston rings typically requires a teardown and overhaul. Since you can find your pistons at the bottom of the combustion chambers, reaching them requires disassembling most of the engine. With so much labor required for this job, overhauling the whole engine at the same time is typically the most cost-effective option. 

For more information on an engine overhaul, contact a company like Black Dog Oil Field Services LTD.