ISO 6623:2013

INTERNATIONAL ISO
STANDARD 6623
Third edition
2013-07-15
Internal combustion engines — Piston
rings — Scraper rings made of cast iron
Moteurs à combustion interne — Segments de piston — Segments
racleurs mixtes en fonte moulée
Reference number
©
ISO 2013
© ISO 2013
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ii © ISO 2013 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Overview . 1
4 Ring types and designation examples . 1
4.1 Types N, NM, E, and EM scraper rings — General features . 1
4.2 Type N . 2
4.3 Type NM . 3
4.4 Type E . 4
4.5 Type EM . 5
5 Common features . 6
5.1 Type N, NM, E, and EM rings — Inside chamfered edges (KI) . 6
5.2 Type NM and EM rings with a partly cylindrical machined (LM) or lapped (LP) peripheral
surface at the bottom running edge . 7
5.3 Type N, NM, E, and EM rings (chromium plated/spray coated) . 7
5.4 Napier or scraper ring with reduced undercut or step (mini Napier/stepped) [RU] . 8
6 Force factors . 8
7 Dimensions .10
Bibliography .26
Foreword
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
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The committee responsible for this document is ISO/TC 22, Road vehicles.
This third edition cancels and replaces the second edition (ISO 6623:2004), of which it constitutes a
minor revision.
iv © ISO 2013 – All rights reserved

Introduction
ISO 6623 is one of a number of series of International Standards dealing with piston rings for reciprocating
[2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
internal combustion engines. Others are ISO 6621, ISO 6622, ISO 6624,
[12] [13] [14] [15] [16]
ISO 6625, ISO 6626, and ISO 6627 (see Bibliography for details).
INTERNATIONAL STANDARD ISO 6623:2013(E)
Internal combustion engines — Piston rings — Scraper
rings made of cast iron
1 Scope
This International Standard specifies the essential dimensional features of scraper rings made of
cast iron, types N, NM, E, and EM, having diameters from 30 mm up to and including 200 mm, used in
reciprocating internal combustion engines for road vehicles and other applications.
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 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications
3 Overview
The scraper ring types are specified in Tables 1 and 2 and Figures 1 to 5. Their common features and
the dimensions of those features are specified in Tables 3 to 5 and Figures 6 to 9. Tables 6 and 7 give
the force factors for the different ring types, while Tables 8 and 9 give the dimensions and forces of the
scraper rings.
Tables 8 and 9, respectively, offer a choice between the following two radial wall thicknesses:
— radial wall thickness “regular”;
— radial wall thickness “D/22”.
The common features and dimensional tables presented in this International Standard constitute a
broad range of variables and the designer, in selecting a particular ring type, shall 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 his/her selection.
4 Ring types and designation examples
4.1 Types N, NM, E, and EM scraper rings — General features
The general features of types N, NM, E, and EM scraper rings are shown in Figure 1.
NOTE See Tables 8 and 9 for dimensions and forces.
Key
a See 4.2, 4.3, 4.4, and 4.5 and Figures 2, 3, 4, and 5 for detail X of N, NM, E, and EM, respectively.
Figure 1 — Types N, NM, E, and EM
4.2 Type N
4.2.1 Napier ring (undercut step)
The general features of type N Napier rings with an undercut step shall be in accordance with Figures 1
and 2, except for rings h < 1,5 mm.
Key
1 reference plane
2 top side identification mark
a
When the ring is closed, this edge shall be in contact with the cylinder bore.
b
See Table 1.
Figure 2 — Type N (Detail X of Figure 1)
2 © ISO 2013 – All rights reserved

Table 1 — r dimensions
Dimensions in millimetres
r
d
max.
30 ≤ d < 175 0,3
175 ≤ d ≤ 200 0,7
4.2.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6623, being a cast iron Napier
ring with a straight-faced peripheral surface (N), of nominal diameter d = 90 mm (90), of radial wall thickness
“regular”, of nominal ring width h = 2,5 mm (2,5), made of non-heat-treated grey cast iron subclass 12 (MC12),
and with chamfered internal edges (KI):
Piston ring ISO 6623 N - 90 × 2,5 - MC12/K I
NOTE Parameters in parentheses are used in the ISO ring designation.
4.3 Type NM
4.3.1 Napier ring (undercut step), taper faced
The general features of type NM Napier rings with an undercut step, taper faced, shall be in accordance
with Figures 1 and 3, except for rings h < 1,5 mm.
Key
1 reference plane
2 top side identification mark
a
See Table 1.
Figure 3 — Type NM (Detail X of Figure 1)
Table 2 — Taper
Dimensions in minutes
Uncoated rings and chromium-plated or spray-coated rings
with peripheral surface ground
Code
a
Taper Tolerance
M2 30
+60
M3 60
M4 90
a
For chromium-plated rings with a tapered peripheral surface that is not ground, the
+70
tolerance shall be increased by 10 (e.g. M3=60 ).
4.3.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6623, being a cast iron Napier
ring with a 90′ taper-faced peripheral surface (NM4), of nominal diameter d = 90 mm (90), of radial wall thickness
“regular”, of ring width h = 2,5 mm (2,5), made of heat-treated grey cast iron subclass 21 (MC21), and phosphated
on all sides (PO):
Piston ring ISO 6623 NM4 - 90 × 2,5 - MC21/PO
NOTE Parameters in parentheses are used in the ISO ring designation.
4.4 Type E
4.4.1 Scraper ring (stepped)
The general features of type E stepped scraper rings shall be in accordance with Figures 1 and 4.
Key
1 reference plane
2 top side identification mark
a
When the ring is closed, this edge shall be in contact with the cylinder bore.
b
See Table 1.
Figure 4 — Type E (Detail X of Figure 1)
4 © ISO 2013 – All rights reserved

4.4.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6623, being a cast iron
scraper ring with a straight-faced peripheral surface (E), of nominal diameter d = 90 mm (90), of nominal ring
width h = 2,5 mm (2,5), of radial wall thickness “regular”, made of non-heat-treated grey cast iron subclass 12
(MC12), and with an inlaid spray coating on the peripheral surface, and minimum thickness 0,1 mm (SC2F):
Piston ring ISO 6623 E - 90 × 2,5 - MC12/SC2F
NOTE Parameters in parentheses are used in the ISO ring designation.
4.5 Type EM
4.5.1 Scraper ring (stepped), taper faced
The general features of type EM scraper rings, stepped and taper faced, shall be in accordance with
Figures 1 and 5.
Key
1 reference plane
2 top side identification mark
a
See Table 1.
b
See Table 2.
Figure 5 — Type EM (Detail X of Figure 1)
4.5.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6623, being a cast iron scraper
ring with a 30′ taper-faced peripheral surface (EM2), of nominal diameter d = 90 mm (90), of nominal ring width
h = 2,5 mm (2,5), of radial wall thickness “regular”, made of heat-treated grey cast iron subclass 22 (MC22), and
with inside chamfered edges (KI):
Piston ring ISO 6623 EM2 - 90 × 2,5 - MC22/KI
NOTE Parameters in parentheses are used in the ISO ring designation.
5 Common features
5.1 Type N, NM, E, and EM rings — Inside chamfered edges (KI)
Dimensions in millimetres
a) For nominal KI ≥ 0,3 b) For nominal KI < 0,3
Key
1 top side identification mark
Figure 6 — Inside chamfered edges (KI)
Table 3 — KI dimensions
Dimensions in millimetres
d KI
30 ≤ d < 50 0,2 max.
a
50 ≤ d < 125 0,3 ± 0,15
125 ≤ d < 175 0,4 ± 0,15
175 ≤ d ≤ 200 0,6 ± 0,2
a
KI = 0,2 max. for rings 50 < d < 60 and h < 1,5
1 1
6 © ISO 2013 – All rights reserved

5.2 Type NM and EM rings with a partly cylindrical machined (LM) or lapped (LP) pe-
ripheral surface at the bottom running edge
a) Feature: machined = Code: LM b) Feature: lapped = Code: LP
Figure 7 — NM and EM rings with partly cylindrical peripheral surface
Table 4 — Axial dimensions of cylindrical part of peripheral surface h
Dimensions in millimetres
a a
h h h
1 24 24
max. each side of the gap up to 30° max.
1,2 0,4 0,6
1,5 0,5 0,8
1,75 0,6 1,0
2,0 0,7 1,2
2,5 0,9 1,4
3 ≤ h ≤ 4 1,1 1,8
a
Partly cylindrical peripheral surface shall be visible.
5.3
...