ISO 6623:2013

Overview

ISO 6623:2013 specifies essential dimensional features and related requirements for scraper piston rings made of cast iron (types N, NM, E, EM) used in reciprocating internal combustion engines for road vehicles and other applications. The standard applies to rings with nominal diameters from 30 mm up to and including 200 mm and defines geometry, tolerances, coatings, force factors and designation examples to support consistent design, manufacture and quality control.

Key topics and technical requirements

• Ring types and geometry
  • Type N (Napier / undercut step), NM (Napier taper-faced), E (stepped scraper), EM (stepped taper-faced).
  • Diagrams and detail views (Figures 1–5) show reference planes, top-side marks, and running-edge features.
• Dimensional tables
  • Comprehensive tables for nominal diameters, radial wall thickness options (“regular” and “D/22”), ring widths, closed gaps, axial step widths and tolerances (Tables 8–9).
  • Example designation format included (e.g., “Piston ring ISO 6623 NM4 - 90 × 2,5 - MC21/PO”).
• Peripheral surface options
  • Taper codes (e.g., M2 ≈ 30′, M3 ≈ 60′, M4 ≈ 90′) with tolerances for ground or unground plated surfaces.
  • Partly cylindrical machined (LM) or lapped (LP) bottom running-edge options and axial extents (Figure 7, Table 4).
• Edge and coating specifications
  • Inside chamfer (KI) sizes by diameter range and tolerances (Table 3).
  • Coating/plating options with minimum thicknesses: chromium plating (CRF, CR1, CR2) and spray/inlaid coatings (SC1F–SC4F) with specified thicknesses (e.g., CRF 0.005 mm, CR1 0.05 mm, CR2 0.1 mm; SC1F 0.05 mm, SC2F 0.1 mm, etc.).
• Force factors and corrections
  • Tangential and diametral force data and correction factors for coatings, KI and materials (Tables 6–7). Designers must correct tabulated forces when using materials/coatings different from the baseline grey cast iron.
• Special variants
  • Mini Napier/stepped (RU) - reduced undercut dimensions and adjusted force factors.

Practical applications and users

ISO 6623:2013 is intended for:

• Engine designers and OEMs specifying piston ring geometry for road-vehicle and industrial reciprocating engines.
• Piston-ring manufacturers and foundries producing cast iron scraper rings.
• Quality engineers, procurement teams and test laboratories verifying conformance to dimensional and coating requirements.
• Aftermarket parts suppliers ensuring interchangeability and reliable sealing/scraping performance.

Benefits include standardized interchangeability, reliable sealing/scraping behavior, and clearer supplier specifications for production and inspection.

Related standards

• ISO 6621 series (notably ISO 6621-4) - referenced for general piston ring specifications and force corrections.
• Other ISO piston-ring parts (ISO 6621, ISO 6622, ISO 6624–6627) for complementary ring types and test methods.

Keywords: ISO 6623:2013, piston rings, scraper rings, cast iron, Napier ring, scraper ring dimensions, ring coatings, engine design, ring force factors.