Piston ring problems

by Had Robinson
updated January 20, 2022

Installation and removal

This should be done without tools.

Use your fingernails to gently spread the tips of the ring so that it will just clear the piston.  Slide off/on the piston ring.  Be sure to clean the piston ring lands with the old ring.  Use a file to nick the outer and inner ring surface and break the ring in half.  Use 2 stroke oil to coat the new ring before reinstallation.  When reinstalling be certain that the tips of the ring are on either side of the holding pin that is in the lands (groove) on the piston.  If the ring is not lined up properly, the piston will not slide into the cylinder.  If there are markings on the flats of the ring, make sure they are on the top side when installing it.

Worn rings

Like everything else in an engine, piston rings will wear out.  If the cylinder lacks oil while running, even briefly, ring wear (and permanent damage) will occur within a minute or two.

The photo below shows a new ring on the left and a damaged ring on the right.  If your ring looks much different than the one on the left, it should be replaced.  The ring on the right is from a new engine that had no lubrication for a brief period.  The pilot had fuel that was contaminated with water (he sent me a sample).  However, from the looks of the ring, he probably forgot to mix oil with the gasoline.  Typically, when lubrication is lost, the piston will seize from overheating, as this one probably did.

Notice that the chromium/nitride plating is missing from the outer edges of the damaged ring (red arrows) and the ring core is exposed and badly worn.  Instead of relatively sharp outer edges, the ring is slightly rounded and is unable to do its job of sealing the combustion chamber.

The black arrow shows what is left of the badly scuffed plating.  If the pilot had run the engine a bit more, there would have been nothing left of the plating.  When lubrication is lost while the engine is running, the cylinder, piston, and ring wear is severe and all of the components must be replaced.

The piston ring is necessary to seal the combustion chamber and to transfer heat from the piston to the cylinder walls.  If the cylinder walls have had the honing marks worn down, the cylinder should be re-honed or replaced.  At this time, it is cheaper to replace the cylinder.

photo courtesy of Precision Surfacing Solutions