Piston ring problems

by Had Robinson

Installation and removal

This should be done without tools.  Simply 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.  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 can wear out and/or be damaged.  Below is a close-up photo of a Top 80 ring from a new engine that had no lubrication for a brief period (right ring).  The pilot had fuel that was contaminated with water (he sent me a sample).  However, he may have forgotten to mix oil with the gasoline, despite his claims to the contrary.  Typical when lubrication is lost, the piston in the engine will seize from overheating, as this one probably did.

The piston ring is necessary to seal the combustion chamber and to transfer heat from the piston to the cylinder walls.

A new ring is on the left, the damaged ring is on the right.  Notice that the chromium/nitride plating is missing from the outer edges of the ring (red arrows) and the core of the ring 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, cylinder, piston, and piston ring wear is severe and all of the components must be replaced.

Top 80 damaged piston ring