This is the piston ring for the UMS 7-90cc engine, the seven-cylinder 90cc four-stroke radial from UMS.
The part itself is the piston rings, which seal compression and control oil on the cylinder wall.
Why it is replaced: rings are a wear item and are replaced at overhaul; worn rings show as falling compression, rising oil consumption and hard starting. Supplied as a pack of 4, which is how these small parts are normally bought — you rarely need just one.
Fitting note: Check ring end gap in the bore before fitting, and stagger the gaps on assembly.
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