BS ISO 6621-5-2020 Internal combustion engines一Piston rings Part 5: Quality requirements.
This document specifies quality aspects that can be defined but that are not normally found on a
drawing specification.
It covers the following:
— single-piece piston rings ogrey cast iron or steel;
— multi-piece piston rings (oil control rings) consisting of cast iron parts and spring components; and
— single-piece and multi-piece oil control rings of steel. i.e. oil control rings in the form of strip steel components or steel segments (rails) with spring expander components.
In addition to specifying some of the limits of acceptance relating to inspection measuring principles (covered by Iso 6621-2), this document also covers those features for which no recognized quantitative measurement procedures exist and which are only checked visually with normal eyesight (glasses if worn normally) and without magnification. Such features (superficial defects) are additional to the standard tolerances of ring width, radial wall thickness and closed gap.
This document does not establish acceptable quality levels (AQL), it being left to manufacturer and customer to decide the appropriate levels jointly. In this case, the recommendations of ISO 2859-1 are followed.
This document specifies the quality requirements of piston rings for reciprocating internal combustion engines for road vehicles and other applications. It is applicable to all such rings of a nominal diameter from 30 mm up to and including 200 mm.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 662 1-1, internal combustion engines — Piston rings — Part 1: Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 662 1-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at
— IEC Electropedia: available at
4 Visible defects
4.1 General
Visible defects are divided into two principle classes as described in 42 to 4.5.
The first class covers those defects frequently found in castings and includes such defects as porosity, sand inclusions, cavities, etc.
The second class of defect covers mechanical abrasions which may occur during forming, machining or handling of the rings, and includes scratches, dents, chipping, burrs and cracks.
Inspection of piston rings for such defects is generally carried out visually, without magnification, by inspectors having normal eyesight, corrected if necessary.
It is not intended that every ring be rigorously inspected for size and distribution of defects, but rather that the values given in the tables and text be used as a general guide. However, in case of doubt, the values given should be used as the means of judging the quality of the rings.BS ISO 6621-5 pdf download.