Overview
ISO 28741:2023 - Road vehicles - Spark-plugs and their cylinder head housings - Basic characteristics and dimensions - is a consolidated international standard that specifies the main properties, dimensions and design requirements for spark plugs and their cylinder head housings used with spark‑ignited engines. Applicable beyond road vehicles, the standard harmonizes thread sizes, seating types, terminal interfaces and key dimensional features so manufacturers, OEMs and service suppliers can ensure interchangeability and reliable ignition-system fitment.
Key Topics
- Scope and exclusions: Defines general requirements for spark plugs and housings; excludes screened and waterproof spark plugs (see ISO 3412, ISO 3895, ISO 3896).
- Thread sizes and tolerances: Covers standard metric thread sizes (examples include M10, M12, M14, M18) and references ISO thread standards (ISO 68‑1, ISO 261, ISO 965 series) for limiting dimensions and tolerances.
- Seating types and reach: Specifies flat seating and conical seating interfaces, and defines spark plug reach (short, medium, long, extended, etc.) and projection to avoid piston interference.
- High‑voltage terminals: Standardizes terminal types - SAE (solid post), cup terminals, and threaded terminals - including dimensional and measurement rules for reliable ignition lead connection.
- Gaskets and sealing: Defines gasket function and required thickness after initial torqueing for flat seats to ensure gas‑tight seals.
- Installation torque: Provides guidance on installation tightening torque and cautions on factors (thread lubrication, head material, plating) that affect torque requirements.
- Dimensional diagrams and annexes: Includes detailed figures, tables and normative annexes for half‑thread plugs, optional terminals, and combination housings.
Applications
- Automotive OEMs and component manufacturers use ISO 28741:2023 to design and produce compatible spark plugs, spark plug shells, and cylinder head housings.
- Engine designers and calibration engineers rely on defined reach, projection, and seating specifications to ensure combustion chamber clearance and ignition reliability.
- Aftermarket parts suppliers and service technicians use the standard to select correct replacement plugs, matching thread, seating and terminal types.
- Regulatory and quality teams use the standard to harmonize procurement, testing interfaces and conformity with international thread/tolerance rules.
Related Standards
Keywords: ISO 28741:2023, spark plugs, cylinder head housings, spark plug dimensions, thread sizes, ignition terminals, spark plug reach, installation torque.