ISO 9457-2:1994

Overview

ISO 9457-2:1994 is Part 2 of the ISO 9457 series and defines the metric modules, tooth counts and tooth geometry required to ensure interchangeability of starter motor pinions with a 20° pressure angle. Intended for starter motors used on reciprocating internal combustion engines for road vehicles, the standard supports consistent manufacturing and reliable mechanical mating between pinions and starter ring gears.

The document was developed by ISO/TC 22 (Road vehicles), subcommittee SC 15 (Interchangeability of commercial vehicle and bus components). An informative annex lists related bibliographic references for tolerances and gear notation.

Key Topics

• Scope and purpose: Establishes required metric modules, numbers of teeth and other tooth characteristics so pinions are interchangeable across manufacturers.
• Allowed metric modules: The standard lists combinations of metric module values and permissible tooth counts (examples in the document include modules such as 2.25, 2.5, 3.0 and 4.0 for specific tooth counts).
• Tooth proportions and dimensions: Denture dimensions are derived from specified tooth proportion values (h1/m), a standard dedendum ratio, and a maximum tool radius. Detailed dimensions and control values (for example, runout/clearance W2) are tabulated in the standard.
• Design notes and cautions: The standard cautions on the drive-ratio and acoustic performance - notably that pinions with eight teeth may generate higher noise and require careful attention to the drive ratio and noise control.
• Chamfering and unspecified details: If tooth chamfers are required, they must be on the opposite face to the leading side. Dimensions or prescriptions not covered may be left to the manufacturer.

Applications

ISO 9457-2:1994 is practical for engineers, component manufacturers and quality managers involved in:

• Designing and specifying starter motor pinions for road vehicles and automotive starter assemblies.
• Ensuring interchangeability between suppliers and legacy components during repair or OEM assembly.
• Selecting appropriate module and tooth-count combinations to control engagement quality, mesh ratio and acoustic behavior of starter gear trains.
• Producing shop drawings and inspection criteria based on standardized tooth proportions and dimensional tables.

Benefits include reduced rework, predictable fit and performance across suppliers, and clearer communication between designers and manufacturers.

Related Standards

• ISO 9457-1 - Part 1: common-use starter motor pinions (complements Part 2).
• ISO 286-2:1988 - System of tolerances and fits (referenced for tolerance classes).
• ISO 701:1976 - Gear data notation and symbols.

For implementation, consult the tabulated dimensions and notes in ISO 9457-2:1994 and coordinate tolerance classes with ISO 286-2 to ensure correct fits and manufacturing control.