ISO 21342:2019

INTERNATIONAL ISO
STANDARD 21342
First edition
2019-05
Synchronous belt drives — Automotive
belts and pulleys
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative reference . 1
3 Terms and definitions . 1
4 Profiles . 1
5 Belt designation . 2
6 Belt dimensions and tolerances . 2
6.1 Belt tooth dimensions — Trapezoidal tooth belts of types ZA and ZB . 2
6.2 Belt tooth dimensions — Curvilinear tooth belts of types ZH and YH . 3
6.3 Belt tooth dimensions — Curvilinear tooth belts of types YR and ZR . 4
6.4 Belt tooth dimensions — Curvilinear tooth belts of types YS and ZS . 5
6.5 Belt pitch length and tolerances . 6
6.6 Belt widths and tolerances . 7
7 Pitch length measurement . 7
7.1 Measuring fixture. 7
7.2 Total measuring force . 8
7.3 Procedure . 8
7.4 Dimensions and clearance between measuring pulley and belt, and measuring
pulley grooves . 9
8 Lateral runout measurement .12
8.1 Fixture .12
8.1.1 Belt .12
8.1.2 Pulleys .12
8.2 Measuring device .12
8.3 Procedure .12
8.4 Results .12
9 Pulley types .13
10 Pulley designation .13
11 Pulley groove profile .14
11.1 Pulleys of types ZA and ZB (involute groove profile) .14
11.2 Pulleys of types ZH and YH .15
11.3 Pulleys of types ZR and YR.16
11.4 Pulleys of types ZS and YS .16
12 Pulley dimensions and tolerances .17
12.1 Pitch tolerances .17
12.2 Pulley outside diameter tolerances .17
12.3 Minimum pulley width .18
12.4 Flange dimensions .18
12.5 Other pulley tolerances .19
12.5.1 Axial runout.19
12.5.2 Radial runout .20
12.5.3 Parallelism .20
12.5.4 Taper.20
13 Quality specification .20
Foreword
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electrotechnical standardization.
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This document was prepared by Technical Committee ISO/TC 41, Pulleys and belts (including vee belts),
Subcommittee SC 4, Synchronous belt drives.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
This first edition of ISO 21342 cancels and replaces ISO 9010:1997 and ISO 9011:1997.
iv © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 21342:2019(E)
Synchronous belt drives — Automotive belts and pulleys
1 Scope
This document specifies the characteristics of synchronous endless belts and their related pulleys for
use in automotive applications such as engine camshaft drives.
The characteristics include:
— belt pitch spacing;
— belt nominal tooth dimensions;
— belt width and width tolerance;
— belt pitch length and pitch length tolerance;
— pulley groove dimensions and tolerances;
— pulley tolerances and quality specifications.
Test methods for measuring belt pitch length and lateral runout are also included.
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 254, Belt drives — Pulleys — Quality, finish and balance
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:
— ISO Online browsing platform: available at https: //www .iso .org/obp.
— IEC Electropedia: available at http: //www .electropedia .org/
4 Profiles
The following profiles for synchronous drives for automotive applications are standardized:
— type ZA: trapezoidal tooth;
— type ZB: trapezoidal tooth;
— type ZH: curvilinear tooth, "H" system;
— type YH: curvilinear tooth, "H" system;
— type ZR: curvilinear tooth, "R" system;
— type YR: curvilinear tooth, "R" system;
— type ZS: curvilinear tooth, "S" system;
— type YS: curvilinear tooth, "S" system.
5 Belt designation
A belt is designated by a series of numbers and letters as follows:
a) the first set of numbers indicates the number of teeth;
b) the first letter indicates tooth pitch;
c) the second letter indicates tooth profile;
d) The second set of numbers indicates the width in millimetres.
EXAMPLE
6 Belt dimensions and tolerances
6.1 Belt tooth dimensions — Trapezoidal tooth belts of types ZA and ZB
The nominal belt tooth dimensions for trapezoidal tooth belts of types ZA and ZB are shown in Figure 1
and given in Table 1.
2 © ISO 2019 – All rights reserved

Key
1 tooth pitch (p )
b
2 tooth angle (2β)
3 height (h )
s
4 pitch line differential (a)
5 root radius (r )
r
6 tip radius (r )
a
7 tooth height (h )
t
8 tooth width (S)
Figure 1 — Nominal tooth dimensions (profile) for types ZA and ZB
Table 1 — Nominal tooth dimensions for types ZA and ZB
Nominal profile
Key number Symbol
Type ZA Type ZB
1 p 9,525 9,525
b
2 2β 40 40
3 h 4,1 4,5
s
4 a 0,686 0,686
5 r 0,51 1,02
r
6 r 0,51 1,02
a
7 h 1,91 2,29
t
8 S 4,65 6,12
6.2 Belt tooth dimensions — Curvilinear tooth belts of types ZH and YH
The nominal belt tooth dimensions for curvilinear tooth belts of types ZH and YH are shown in Figure 2
and given in Table 2.
Key
1 tooth pitch (p )
b
2 height (h )
s
3 pitch line differential (a)
4 root radius (r )
r
5 tooth height (h )
t
6 tooth radius (R)
7 vertical offset (Y)
8 root radius distance (S )
r
Figure 2 — Nominal tooth dimensions (profile) for types ZH and YH
Table 2 — Nominal tooth dimensions for types YH and ZH
Dimensions in millimetres
Angles in degrees
Nominal profile
Key number Symbol
Type YH Type ZH
1 p 8 9,525
b
2 h 5,2 5,5
s
3 a 0,686 0,686
4 r 0,64 0,76
r
5 h 3,04 3,5
t
6 R 2,11 2,45
7 Y 0,93 1,05
8 S 2,84 3,27
r
6.3 Belt tooth dimensions — Curvilinear tooth belts of types YR and ZR
The nominal tooth dimensions for curvilinear tooth belts of types YR and ZR are shown in Figure 3 and
given in Table 3.
4 © ISO 2019 – All rights reserved

Key
1 tooth pitch (p )
b
2 tooth angle (2β)
3 height (h )
s
4 pitch line differential (a)
5 root radius (r )
r
6 tooth height (h )
t
7 tooth width (S)
8 Y = kX
Figure 3 — Nominal tooth dimensions (profile) for YR and ZR
Table 3 — Nominal tooth dimensions for types YR and ZR
Dimensions in millimetres
Angles in degrees
Nominal profile
Key number Symbol
Type YR Type ZR
1 p 8 9,525
b
2 2β 30 32
3 h 5,1 5,4
s
4 a 0,75 0,75
5 r 0,8 1,00
r
6 h 2,8 3,2
t
7 S 5,3 5,5
Tooth form parameter k 1,692 1,228
6.4 Belt tooth dimensions — Curvilinear tooth belts of types YS and
...