ISO 6624-1:2017

Internal combustion engines — Piston rings — Part 1: Keystone rings made of cast iron

ISO 6624-1:2017 specifies the essential dimensional features of keystone rings made of cast iron, types T, TB, TBA, TM, K, KB, KBA and KM, having diameters from 70 mm up to and including 200 mm, used in reciprocating internal combustion piston engines.

Moteurs à combustion interne — Segments de piston — Partie 1: Segments trapézoïdaux en fonte

General Information

• Status: Published
• Publication Date: 26-Apr-2017
• ICS: 43.060.10 - Engine block and internal components
• Technical Committee: ISO/TC 22/SC 34 - Propulsion, powertrain and powertrain fluids
• Drafting Committee: ISO/TC 22/SC 34/WG 4 - Piston rings
• Current Stage: 9060 - Close of review
• Due Date: 02-Sep-2022

RELATIONS

• Revises: ISO 6624-1:2001 - Internal combustion engines — Piston rings — Part 1: Keystone rings made of cast iron
• Effective Date: 04-Nov-2015

Standards Content (sample)

INTERNATIONAL ISO
STANDARD 6624-1
Third edition
2017-04
Internal combustion engines —
Piston rings —
Part 1:
Keystone rings made of cast iron
Moteurs à combustion interne — Segments de piston —
Partie 1: Segments trapézoïdaux en fonte
Reference number
ISO 6624-1:2017(E)
ISO 2017
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ISO 6624-1:2017(E)
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© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
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ISO 6624-1:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative reference ......................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Overview ....................................................................................................................................................................................................................... 1

5 Ring types and designation examples ............................................................................................................................................ 1

5.1 Type T — Straight faced keystone ring 6° ....................................................................................................................... 1

5.1.1 General features................................................................................................................................................................ 1

5.1.2 Designation ........................................................................................................................................................................... 2

5.2 Type TB — Symmetrical barrel faced keystone ring 6° ....................................................................................... 2

5.2.1 General features................................................................................................................................................................ 2

5.2.2 Designation ........................................................................................................................................................................... 4

5.3 Type TBA — Asymmetrical barrel faced keystone ring 6° ................................................................................ 4

5.3.1 General features................................................................................................................................................................ 4

5.3.2 Designation ........................................................................................................................................................................... 5

5.4 Type TM — Taper faced keystone ring 6° ........................................................................................................................ 5

5.4.1 General features................................................................................................................................................................ 5

5.4.2 Designation ........................................................................................................................................................................... 6

5.5 Type K — Straight faced keystone ring 15° .................................................................................................................... 7

5.5.1 General features................................................................................................................................................................ 7

5.5.2 Designation ........................................................................................................................................................................... 7

5.6 Type KB — Symmetrical barrel faced keystone ring 15° ................................................................................... 7

5.6.1 General features................................................................................................................................................................ 7

5.6.2 Designation ........................................................................................................................................................................... 8

5.7 Type KBA — Asymmetrical barrel faced keystone ring 15° ............................................................................ 8

5.7.1 General features................................................................................................................................................................ 8

5.7.2 Designation ........................................................................................................................................................................... 9

5.8 Type KM — Taper faced keystone ring 15° .................................................................................................................... 9

5.8.1 General features................................................................................................................................................................ 9

5.8.2 Designation ........................................................................................................................................................................10

6 Common features ..............................................................................................................................................................................................11

6.1 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Inside chamfered edges (KI) ..................................11

6.2 Type T, TB, TBA, TM, K, KB, KBA, KM rings (positive twist type) internal bevel or

internal step top side ......................................................................................................................................................................11

6.3 Type TM or KM rings with partly cylindrical machined (LM) or lapped (LP)

peripheral surface .............................................................................................................................................................................12

6.4 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Plating/coating configuration ..............................13

6.4.1 Uncoated rings ................................................................................................................................................................13

6.4.2 Chromium plated, PVD coated or spray coated rings ...................................................................14

7 Force factors ...........................................................................................................................................................................................................16

8 Dimensions ..............................................................................................................................................................................................................16

Bibliography .............................................................................................................................................................................................................................24

© ISO 2017 – All rights reserved iii
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ISO 6624-1:2017(E)
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

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on 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

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO’s adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: w w w . i s o .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 34,

Propulsion, powertrain and powertrain fluids.

This third edition cancels and replaces the second edition (ISO 6624-1:2001), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— PVD coating thickness has been included with a new Table 8;
— updates have been made regarding technology improvements.
iv © ISO 2017 – All rights reserved
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ISO 6624-1:2017(E)
Introduction

ISO 6624 belongs to the series of International Standards dealing with piston rings for reciprocating

internal combustion engines. Others are ISO 6621, ISO 6622, ISO 6623, ISO 6625, ISO 6626 and ISO 6627

(see Bibliography for details).

The common features and dimensional tables presented in this document constitute a broad range of

variables and, in selecting a particular ring type, the designer must bear in mind the conditions under

which it will be required to operate.
[4]

It is also essential that the designer refer to the specifications and requirements of ISO 6621-3 and

ISO 6621-4 before completing a selection.
© ISO 2017 – All rights reserved v
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INTERNATIONAL STANDARD ISO 6624-1:2017(E)
Internal combustion engines — Piston rings —
Part 1:
Keystone rings made of cast iron
1 Scope

This document specifies the essential dimensional features of keystone rings made of cast iron, types

T, TB, TBA, TM, K, KB, KBA and KM, having diameters from 70 mm up to and including 200 mm, used in

reciprocating internal combustion piston engines.
2 Normative reference

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 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications

3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Overview

The keystone ring types are specified in Tables 1 to 3 and Figures 1 to 8. Their common features and

the dimensions of those features are specified in Tables 4 to 8 and Figures 9 to 16. Tables 9 and 10 give

the force factors for the different types of ring, while Table 11 and Table 12 give the dimensions and

forces of keystone rings 6° and 15°, respectively.
5 Ring types and designation examples
5.1 Type T — Straight faced keystone ring 6°
5.1.1 General features
See Table 10 for dimensions and forces.
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ISO 6624-1:2017(E)
Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 1 — Type T
5.1.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624–1, being a cast

iron, 6° keystone ring with a straight faced peripheral surface (T), of nominal diameter d = 90 mm (90) and

nominal width h = 2,5 mm (2,5), made of grey cast iron, subclass 12 (MC12), and having a chromium plated

peripheral surface with a minimum thickness of 0,1 mm (CR2). Parameters in parenthesis are used in the ISO

ring designation:
Piston ring ISO 6624-1 T-90 × 2,5-MC12/CR2
5.2 Type TB — Symmetrical barrel faced keystone ring 6°
5.2.1 General features
See Table 10 for dimensions and forces.
2 © ISO 2017 – All rights reserved
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ISO 6624-1:2017(E)
Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 2 — Type TB
Table 1 — Symmetrical barrel dimensions
Dimensions in millimetres
h h h h t , t h
1 25 26 27 2 3 8
Tolerance
2,0 0,40 1,00 ±0,30 1,60 1,2
0,003...0,015
2,5 0,45 1,25 ±0,40 2,05 1,6
3,0 0,50 1,50 2,50 2,0
±0,50 0,005...0,020
3,5 0,55 1,75 2,95 2,4
4,0 0,60 2,00 3,40 2,8
±0,60 0,005...0,023
4,5 0,65 2,25 3,85 3,2

Gauge width h , informative only, shall be used only if agreed between manufacturer and customer.

© ISO 2017 – All rights reserved 3
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ISO 6624-1:2017(E)
5.2.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624–1, being a cast iron, 6°

keystone ring with a symmetrical barrel faced peripheral surface (TB), of nominal diameter d = 90 mm (90) and

nominal ring width h = 2,5 mm (2,5), made of heat-treated martensitic spheroidal graphite cast iron, subclass 53

(MC53), and having a semi-inlaid spray coating on the peripheral surface with a minimum thickness of 0,2 mm

(SC4E). Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6624-1 TB-90 × 2,5-MC53/SC4E
5.3 Type TBA — Asymmetrical barrel faced keystone ring 6°
5.3.1 General features
See Table 10 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 3 — Type TBA
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ISO 6624-1:2017(E)
Table 2 — Asymmetrical barrel dimensions
Dimensions in millimetres
a b b
h h h h t t
1 25 26 27 2 3
Tolerance
2,00 0,40 0,60 ±0,20 1,50 0...0,007 0,009...0,030
2,50 0,45 0,70 1,80 0,011...0,035
±0,25 0...0,008
3,00 0,55 0,80 2,10 0,012...0,038
3,50 0,60 0,90 2,40 0,012...0,040
±0,30 0...0,009
4,00 0,65 0,95 2,80 0,013...0,045
4,50 0,70 1,05 ±0,35 3,20 0...0,010 0,015...0,050
h may be lowered for rings with reduced edge dimensions.
t or t or both may be varied as agreed between manufacturer and customer.
2 3
5.3.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624–1, being a cast iron,

6° keystone ring with an asymmetrical barrel faced peripheral surface (TBA), of nominal diameter d = 90 mm

(90) and nominal ring width h = 2,5 mm (2,5), made of heat-treated martensitic spheroidal graphite cast iron,

subclass 53 (MC53), and having a semi-inlaid spray coating on the peripheral surface with a minimum thickness

of 0,2 mm (SC4E). Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-1 TBA-90 × 2,5-MC53/SC4E
5.4 Type TM — Taper faced keystone ring 6°
5.4.1 General features
See Table 10 for dimensions and forces.
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ISO 6624-1:2017(E)
Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 4 — Type TM
Table 3 — Taper
Dimensions in minutes
Internal twist feature de-
Code Taper Tolerance signs
Tolerance
+50 +60
M1 10
0 0
M2 30
M3 60
+60 +70
0 0
M4 90
M5 120

For chromium plated rings with a tapered peripheral surface that is not ground, the tolerance

+70 +80

shall be increased by 10 (e.g. M3 = 60 tolerance: ; M3 with internal features = 60 tolerance: ).

0 0
M1 not for rings with partly cylindrical peripheral surface.
5.4.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron, 6°

keystone ring with a 10´ taper faced peripheral surface (TM1), of nominal diameter d = 90 mm (90) and nominal

ring width h = 2,5 mm (2,5), made of heat-treated grey cast iron, subclass 22 (MC22), and phosphate-coated all

over (PO). Parameters in parenthesis are used in the ISO ring designation:
6 © ISO 2017 – All rights reserved
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ISO 6624-1:2017(E)
Piston ring ISO 6624-1 TM1-90 × 2,5-MC22/PO
5.5 Type K — Straight faced keystone ring 15°
5.5.1 General features
See Table 11 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 5 — Type K
5.5.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron,

15° keystone ring with a straight faced peripheral surface (K), of nominal diameter d = 90 mm (90) and nominal

ring width h = 2,5 mm (2,5), made of carbidic cast iron, subclass 32 (MC32), and ferroxide coated all over (FE).

Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6624-1 K-90 × 2,5-MC32/FE
5.6 Type KB — Symmetrical barrel faced keystone ring 15°
5.6.1 General features
See Table 1 for symmetrical barrel dimensions.
See Table 11 for dimensions and forces.
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ISO 6624-1:2017(E)
Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 6 — Type KB
5.6.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron, 15°

keystone ring with a barrel faced peripheral surface (KB), of nominal diameter d = 90 mm (90) and nominal ring

width h = 2,5 mm (2,5), made of malleable cast iron, subclass 41 (MC41), and having an inlaid spray coating on

the peripheral surface with a minimum thickness of 0,2 mm (SC4F). Parameters in parenthesis are used in the

ISO ring designation:
Piston ring ISO 6624-1 KB-90 × 2,5-MC41/SC4F
5.7 Type KBA — Asymmetrical barrel faced keystone ring 15°
5.7.1 General features
See Table 2 for asymmetrical barrel dimensions.
See Table 11 for dimensions and forces.
8 © ISO 2017 – All rights reserved
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ISO 6624-1:2017(E)
Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.

Figure 7 — Type KBA — Correction of details “X” and “Y”: show asymmetry more detailed

5.7.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron 15°

keystone ring with an asymmetrical barrel faced peripheral surface (KBA) of nominal diameter d = 90 mm (90)

and nominal ring width h = 2,5 mm (2,5), made of malleable cast iron, subclass 41 (MC41), and having an inlaid

spray coating on the peripheral surface with a minimum thickness of 0,2 mm (SC4F). Parameters in parenthesis

are used in the ISO ring designation:
Piston ring ISO 6624-1 KBA
...