ISO 6621-4:2015

INTERNATIONAL ISO
STANDARD 6621-4
Third edition
2015-03-15
Internal combustion engines — Piston
rings —
Part 4:
General specifications
Moteurs à combustion interne — Segments de piston —
Partie 4: Spécifications générales
Reference number
©
ISO 2015
© ISO 2015
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Piston ring codes . 1
5 Designation of piston rings . 4
5.1 Designation elements and order . 4
5.2 Designation examples . 5
6 Marking of piston rings . 6
6.1 General . 6
6.2 Mandatory topside identification marking . 6
6.3 Additional marking . 7
7 General characteristics . 7
7.1 Ring shape . 7
7.2 Light tightness . 8
7.3 Closed gap . 8
7.4 Tangential force, F , and diametral force, F , of single piece piston rings . 8
t d
7.5 Tangential force F of multipiece oil control rings as specified in ISO 6626-1, ISO 6626-2,
t
and ISO 6626-3 .12
7.6 Tangential force F of expander/segment oil control rings as specified in ISO 6627 .13
t
8 Notches for preventing ring rotation .13
8.1 Ring joint with internal notch (only for compression rings as specified in ISO 6622 and
ISO 6624) .13
8.2 Ring joint with side notch (only for compression rings as specified in ISO 6622) .15
9 Machining of surfaces .16
9.1 Peripheral surfaces .16
9.2 Side faces .16
9.3 Other surfaces .16
10 Plated, coated, and treated surfaces .17
10.1 Chromium plating on peripheral surfaces .17
10.2 Spray coated peripheral surfaces .20
10.3 Nitrided surfaces .24
10.4 Treated surfaces .25
10.5 Physical vapour deposition coating (PVD) .26
11 Miscellaneous .27
11.1 Cleanliness .27
11.2 Corrosion protection .27
11.3 Packaging .27
12 Traceability (optional) .27
Bibliography .28
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 22, Road vehicles.
This third edition cancels and replaces the second edition (ISO 6621-4:2003), which has been technically
revised.
ISO 6621 consists of the following parts, under the general title Internal combustion engines — Piston
rings:
— Part 1: Vocabulary
— Part 2: Inspection measuring principles
— Part 3: Material specifications
— Part 4: General specifications
— Part 5: Quality requirements
iv © ISO 2015 – All rights reserved

Introduction
ISO 6621 is one of a series of International Standards dealing with piston rings for reciprocating internal
combustion engines. Others are ISO 6622-1, ISO 6622-2, ISO 6623, ISO 6624-1, ISO 6624-2, ISO 6624-3,
ISO 6624-4, ISO 6625, ISO 6626-1, ISO 6626-2, ISO 6626-3, and ISO 6627.
INTERNATIONAL STANDARD ISO 6621-4:2015(E)
Internal combustion engines — Piston rings —
Part 4:
General specifications
1 Scope
This part of ISO 6621 specifies the general characteristics of piston rings for reciprocating internal
combustion engines for road vehicles and other applications (the individual dimensional criteria for
these rings are given in the relevant International Standards). It also provides a system for ring coding,
designation, and marking. 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, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 6507-3, Metallic materials — Vickers hardness test — Part 3: Calibration of reference blocks
ISO 6621-1, Internal combustion engines — Piston rings — Part 1: Vocabulary
ISO 6621-2, Internal combustion engines — Piston rings — Part 2: Inspection measuring principles
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6621-1 apply.
4 Piston ring codes
Codes used for piston rings shall be as given in Table 1, corresponding to their explanatory descriptions.
Table 1 — Codes and descriptions in alphabetical order
Relevant International
Code Description
Standard
B Barrel-faced rectangular ring ISO 6622-1, ISO 6622-2
BA Asymmetrical barrel-faced rectangular ring ISO 6622-1, ISO 6622-2
CR1E . CR2E Peripheral surface chromium plated semi-inlaid design ISO 6621-4
CR1F . CR2F Peripheral surface chromium plated inlaid design ISO 6621-4
CRF . CR4 Peripheral surface chromium plated fully faced design ISO 6621-4
CSN, CSG, CSE Type of coil spring ISO 6626-1, ISO 6626-2
D Bevelled edge oil control ring ISO 6625
D22 Radial wall thickness for “d1/22” ISO 6622-1, ISO 6623
a
Material mark (for alternative materials) at the discretion of the manufacturer.
b
Any other additional marking on customer’s request, which shall be quoted clearly in the order, shall be agreed upon
between manufacturer and customer.
Table 1 (continued)
Relevant International
Code Description
Standard
DSF Coil spring loaded bevelled edge oil control ring ISO 6626-1, ISO 6626-2
DSF-C Coil spring loaded bevelled edge oil control ring,
ISO 6626-1, ISO 6626-2
chromium plated, and profile ground
DSF-CNP Coil spring loaded bevelled edge oil control ring,
ISO 6626-1
chromium plated, not profile ground
DSF-NG Coil spring loaded bevelled edge oil control ring (face
ISO 6626-1
geometry similar type DSF-C or DSF-CNP)
DV Bevelled edge V-groove oil control ring ISO 6625
E Scraper ring (stepped) ISO 6623
EM1 . EM4 Scraper ring (stepped), taper-faced ISO 6623
ES-1 . ES-4 Expander/segment oil control rings ISO 6627
FE Ferro oxided on all sides ISO 6621-4
G Double bevelled oil control ring ISO 6625
...