National foreword

This British Standard is the UK implementation of ISO 12251:2017. It supersedes BS ISO 12251:2011, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee MCE/22, Engines for road vehicles.

A list of organizations represented on this committee can be obtained on request to its secretary.

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2017.

Foreword

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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).

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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 D₁ to D₅ and d₁ to d₅ has been rearranged: same numbers now indicate same position within the assembly of injector and cylinder head;
Figure 5 has been completed in order to show the complete assembly and a new dimension D₃ and bore for capnut space have been added;
D₄ 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 d₃ changed to max. values and max. value for type B.2 changed from 19,1 to 19,2;
dimension D₃ 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.

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:

Type A, where the nozzle capnut is straight (see Figure 4);
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

3 Terms, definitions and symbols

4 General requirements

4.1 Clamp mounting arrangement

4.2 Injector guiding dimensions

4.3 Concentricity of the nozzle shaft

4.4 High pressure connector

5 Dimensions and tolerances

5.1 Type A, clamp mounted CR fuel injectors with straight capnut

5.2 Type B, clamp mounted CR fuel injectors with stepped capnut

6 Other specifications

7 Designation

Bibliography

BS ISO 12251:2017

Diesel engines. Clamp mounted CR fuel injectors. Mounting dimensions

Published:

31 Oct 2017

Withdrawn:

28 Jan 2026