Zuigerveerset std. Ø52,4 SYM 125 AIR 4T

Engineered for the SYM Symphony 125I ST 125cc scooter (2017-2020), this aftermarket piston ring set replaces OEM reference 13010-U3A-000 with equivalent-grade materials and precision tolerances. The piston rings form the dynamic seal between the piston and cylinder wall, a function that directly impacts compression, oil consumption, and exhaust emissions.

The ring set typically includes three rings: a top compression ring, a second compression ring (scraper), and an oil control ring assembly. The top ring must withstand combustion temperatures exceeding 300°C while maintaining a gas-tight seal against pressures above 80 bar. The second ring scrapes excess oil from the cylinder wall and prevents top ring flutter. The oil control ring, consisting of two thin steel rails separated by a expander spring, meters the oil film thickness on the cylinder wall to lubricate the compression rings without allowing excessive oil into the combustion chamber.

Manufactured from cast iron with chromium plating on the top ring face, these rings offer exceptional wear resistance and scuff resistance during the critical break-in period. The chromium layer, typically 0.1-0.2mm thick with a hardness of 800-1,000 HV, provides a low-friction running surface that beds in quickly. The second ring features a taper face or napier hook design that enhances oil scraping action while reducing gas blow-by. The oil control ring expander spring is manufactured from 65Mn steel with a tension calibrated to apply 8-12N of radial force against the cylinder wall.

Technical parameters: bore diameter Ø52.4mm; top ring width 1.2mm; second ring width 1.5mm; oil ring width 2.8mm; top ring material: alloy cast iron with chrome plating; second ring: cast iron with taper face; oil ring: two-piece steel rail with expander; end gap 0.20-0.35mm (top ring, measured in bore).

Replacement is indicated when: compression testing reveals values below 10 bar on a warm engine, oil consumption exceeds 500ml per 1,000 km, blue smoke is visible from the exhaust during deceleration, or during scheduled top-end overhauls at 30,000-40,000 km. Always measure cylinder bore diameter and out-of-round before ordering; if wear exceeds 0.05mm, cylinder re-boring with an oversize piston and rings may be necessary. When installing, stagger the ring end gaps 120° apart and ensure the gaps do not align with the piston pin axis or thrust direction.