paragliding training center
by Had Robinson
This must 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 plenty of 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 or groove on the piston. If the ring is not lined up properly, the piston will not slide into the cylinder!
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. 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 cast iron 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. A damaged cylinder can be replaced or re-bored/honed at this shop for a modest price and get an oversized piston from Miniplane-USA, if needed.