What Are Signs of a Blown Piston Ring?

A blown engine cylinder piston ring is a major engine mechanical problem that severely disrupts the normal operation of a vehicle's engine. Each engine piston has a piston ring that is responsible for sealing engine combustion gases within each engine cylinder, a job that is critical for maintaining proper engine power and function. What follows are the most common signs of a blown piston ring.

Loss of Engine Power

One of the main signs of a blown piston ring is a loss of vehicle engine power. A piston ring, otherwise known as a piston compression ring, is responsible for containing engine combustion and preventing it from blowing past the piston rings into the upper engine chambers, an occurrence that causes a loss of engine combustion pressure, which leads to a significant loss of engine power. A blown piston ring can be verified by performing an engine compression test, a test which measures the compression of each individual engine cylinder.

Exhaust Smoke

A vehicle with a blown piston ring will normally emit exhaust smoke with a bluish tint. By allowing a portion of the engine combustion gases to blow past the piston ring into the main engine crankcase area, these exhaust gases, which are made up of a fair amount of unburned fuel vapors, are emitted out of the vehicle's tailpipe as bluish-colored exhaust smoke, a condition that is more prominent under heavy acceleration or when revving up the vehicle engine.

Increased Vehicle Emissions

Many times a vehicle that has a blown piston ring will fail an exhaust emissions test. This is due to the increased amounts of exhaust gases that are allowed to blow past a blown piston ring. Normally, a fully functional piston ring creates an airtight seal between the piston ring and the wall of the engine cylinder. A blown piston ring will either break completely or develop cracks or chips that allow engine combustion gases to escape past the piston ring and out the vehicle exhaust. These escaping exhaust gases raise the vehicle's emissions profile.

Engine Blow-by

Engine blow-by is a condition that results from engine combustion gases blowing past a blown piston ring and entering the engine head area, where these combustion gases can be visibly seen exiting the engine oil crankcase filler hole or even the carburetor throttle body opening. Engine blow-by is routinely noted during a normal vehicle engine tune-up or some other type of routine vehicle maintenance.

Rough Engine Idle

Due to the engine combustion gases that escape past a blown piston ring, it is common for a vehicle engine with a blown piston ring to idle roughly or erratically. This rough engine idle is due to the loss of engine compression that results from the blown piston ring. The more engine cylinders that have a blown piston ring, the rougher the engine idle will be.

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