ISO 12251:2017

INTERNATIONAL ISO
STANDARD 12251
Second edition
2017-09
Diesel engines — Clamp mounted CR
fuel injectors — Mounting dimensions
Moteurs diesels — Injecteurs de combustible pour rampe commune
fixée par patte — Dimensions de montage
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
4 General requirements . 3
4.1 Clamp mounting arrangement . 3
4.2 Injector guiding dimensions. 4
4.3 Concentricity of the nozzle shaft . 4
4.4 High pressure connector . 5
5 Dimensions and tolerances . 6
5.1 Type A, clamp mounted CR fuel injectors with straight capnut . 6
5.2 Type B, clamp mounted CR fuel injectors with stepped capnut . 8
6 Other specifications .10
7 Designation .10
Bibliography .11
Foreword
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electrotechnical standardization.
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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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URL: www.iso.org/iso/foreword.html.
This document was prepared by ISO/TC 22 Road Vehicles, Subcommitee SC 34 Propulsion, powertrain,
and powertrain fluids.
This second edition cancels and replaces (ISO 12251:2011) which has been technically revised.
The main changes compared to the previous edition are as follows:
— surface specification has been referenced to ISO 1302;
— ISO 2974 has been added for the high pressure connector;
— large D and small d have been interchanged, corresponding to ISO 286-1 (large D for bores, small d
for shafts);
— numbering D to D and d to d has been rearranged: same numbers now indicate same position
1 5 1 5
within the assembly of injector and cylinder head;
— Figure 5 has been completed in order to show the complete assembly and a new dimension D and
bore for capnut space have been added;
— D has been corrected to 24,1 in Table 2 at type A.5 (error in the first edition);
— Table 3 has been changed: tolerances for d changed to max. values and max. value for type B.2
changed from 19,1 to 19,2;
— dimension D and bore for capnut space 19,3 mm have been introduced in Table 4;
— type B.6 has been added in Table 3 and Table 4;
— Bibliography has been added.
iv © ISO 2017 – All rights reserved

INTERNATIONAL STANDARD ISO 12251:2017(E)
Diesel engines — Clamp mounted CR fuel injectors —
Mounting dimensions
1 Scope
This document specifies dimensional requirements for clamp mounted CR fuel injectors and their
corresponding cylinder head features in diesel engines.
According to the injector nozzle capnut, the clamp mounted CR fuel injectors can be divided into
two types:
a) Type A, where the nozzle capnut is straight (see Figure 4);
b) Type B, where the nozzle capnut is stepped (see Figure 5).
Each clamp mounted CR fuel injector type is subdivided by a series of different sizes.
NOTE This differentiation corresponds to the relationship between the two guide diameters of the clamp
mounted CR fuel injectors.
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 1302, Geometrical Product Specifications (GPS) — Indication of surface texture in technical product
documentation
ISO 2974, Diesel engines — 60 female cones for high pressure fuel injection components
3 Terms, definitions and symbols
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
For the purposes of this document, the following symbols apply:
d injector upper guide diameter
d injector shaft diameter
d capnut diameter
d injector lower guide diameter
d injector nozzle shaft diameter
D bore for upper guide diameter
D bore for capnut space
D bore for lower guide diameter
D bore for nozzle shaft
l overa
...