Overview
ISO 7026:1997 specifies dimensional requirements for screw-in injection nozzle holders used on diesel (compression-ignition) engines. It covers four holder types - 20, 21, 21.1 and 27 - designed to accept pintle nozzles size “S”, type “B” (as defined in ISO 2697). The standard is the third edition (1997), superseding ISO 7026:1990 and adding type 21.1.
Key topics and technical requirements
- Scope: Prescribes dimensional and tolerance requirements for mounting screw-in nozzle holders in diesel engines; does not define fuel inlet/return pipe locations.
- Covered types: Holder types 20, 21, 21.1 and 27 for pintle nozzle size S, type B.
- Injector protrusion / screen clearance:
- Type 20 (long version): injector protrusion 1.0 mm – 0.2 mm (see figure 1).
- Types 21 and 21.1 (short version): injector protrusion 13 mm – 0.2 mm (see figure 2).
- Type 27 (with integral thermal screen): protrusion of 14.1 mm – 0.2 mm measured from the top of the thermal screen (see figure 3).
- Dimensions and tolerances: All dimensions are specified in millimetres and shown in the figures; thread diameters are to be considered by flank diameter (characteristic A).
- Design notes for manufacturers:
- Manufacturer must design a thermal screen or gasket so that the distance between face B and the cylinder head top is achieved.
- Determination of the bore/diameter in the cylinder head is left to the engine designer, taking into account maximum-material principle and tolerance stacks to minimize play and avoid injector overheating.
- Unspecified items: Dimensions and requirements not covered by the standard are left to the manufacturer’s discretion.
Applications and users
ISO 7026 is used to ensure mechanical compatibility, interchangeability and correct mounting of screw-in nozzle holders in diesel engines. Typical users:
- Engine manufacturers and designers - for cylinder-head and fuel-system interface design.
- Injector and nozzle-holder component manufacturers - to produce parts to standard dimensions and tolerances.
- OEM suppliers and aftermarket parts producers - to ensure cross-compatibility.
- Service and repair shops, technical authors, and testing laboratories - for reference during maintenance, replacement and validation.
Related standards
- ISO 2697:1974 - defines pintle injector size “S” used by ISO 7026.
- Use ISO 7026 alongside engine-specific standards and manufacturer specifications for full assembly, sealing and fuel-routing details.
Keywords: ISO 7026, diesel engines, screw-in injection nozzle holders, pintle nozzle size S, injector holder types 20 21 21.1 27, dimensions, tolerances, ISO 2697.
Open preview (PDF)Diesel engines — Screw-in injection nozzle holders, types 20, 21, 21.1 and 27 for pintle nozzle size "S", type "B"
