ISO 6626:1989

Overview

ISO 6626:1989 specifies the essential dimensions and key design features for coil-spring-loaded oil control piston rings used in reciprocating internal combustion engines (and similar compressors). The standard covers seven ring types - DSF‑C, DSF‑CNP, SSF, GSF, DSF, DSF‑NG and SSF‑L - for nominal diameters up to 200 mm and axial widths from 3 to 8 mm (divided into 0.5 or 1.0 mm steps). It standardizes geometry, slot arrangement, spring design, materials/finishes and the way tangential force and nominal contact pressure are specified and classified.

Key topics and technical requirements

• Ring types and designation: Defines type codes (e.g., DSF‑C, SSF‑L) and examples for full product identification including diameter, width, material subclass and special treatments.
• Dimensional tables: Comprehensive tabulated dimensions for land widths, groove depths, radial wall thickness, slot lengths (standard and reduced) and cutter diameters for each ring type.
• Slot arrangement: Specifies number and spacing of slots based on ring diameter (e.g., ranges corresponding to 8, 10, 12 or 14 slots) and tolerances for slot/bridge lengths.
• Coil spring details: Standard spring designs (CSN constant‑pitch, CSG constant‑pitch with ground coil diameter, CSE variable‑pitch with ground coil diameter), wire material/heat‑treatment guidance, spring excursion and recommended fixing (latch pin ~180° from ring gap).
• Tangential force & nominal contact pressure: Procedures to specify/compute ring tangential force (spring-dominated), classification into six nominal contact pressure classes (PNE, PNL, PNR, PNM, PNH, PNV), and tolerance rules (actual Ft tolerance +20%).
• Surface finishes & materials: References to material and finish recommendations (e.g., grey cast iron subclasses per ISO 6621‑3) and optional chromium plating layer thickness categories.
• Tolerances and offsets: Limits for land and spring groove offsets and other geometric tolerances referenced to general drawing tolerancing standards.

Applications and users

ISO 6626 is intended for:

• Piston ring manufacturers standardizing production and inspection of coil‑spring oil control rings.
• Engine designers and OEMs selecting ring types and nominal contact pressure for oil control and friction targets.
• Quality/inspection engineers using dimensional tables and tolerances for acceptance testing.
• Aftermarket/remanufacturing and compressor designers where similar reciprocating conditions apply. Practical applications include oil control, blow‑by reduction and friction optimization in automotive, industrial and small engine piston assemblies.

Related standards

• ISO 6621 series (piston ring vocabulary, measuring, materials, general specs, quality)
• ISO 6622, ISO 6623, ISO 6624, ISO 6625 (other piston ring types and guidance)
• ISO 1101 (geometric tolerancing)

Keywords: ISO 6626, piston rings, coil-spring-loaded oil control rings, internal combustion engines, tangential force, nominal contact pressure, piston ring dimensions, spring types, ring design.