Replacement piston rin for the UMS 5-75cc, the five-cylinder 75cc four-stroke radial from UMS.
Function: it is the piston rings, which seal compression and control oil on the cylinder wall.
The reason this ends up on an order: 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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