ISO 9457-1:1991

Overview

ISO 9457-1:1991, "Road vehicles - Metric starter motor pinions - Part 1: Currently used pinions", defines the tooth geometry and dimensional data needed to ensure interchangeability of metric pinions used on starter motors for reciprocating internal combustion engines in road vehicles. This Part 1 covers the currently used series (pressure angle 14°30') and provides the detailed tooth limit dimensions and the base tangent length (W2) used as the inspection value. Dimensions or requirements not given in this part are left to the manufacturer's choice.

Key Topics and Requirements

• Scope: Specifies metric modules, pressure angles, number of teeth and other tooth characteristics necessary for interchangeability of starter motor pinions.
• Pressure angle: Standardized at 14°30' for the pinions covered in this part.
• Metric modules and tooth counts: The standard lists the commonly used metric modules and permitted numbers of teeth for currently used pinions (table of limit dimensions provided in the standard).
• Tooth geometry parameters: Includes addendum modification (coefficient x), tip and root diameters, start and end of active profile, and other tooth limit dimensions.
• Inspection value: Base tangent length (W2) is specified as the inspection control dimension.
• Notation: Symbols and gear notation conform to ISO 701:1976 (illustrated in figure 1 of the document).
• Manufacturer flexibility: Any dimensions or requirements not specified in this part are explicitly left to the manufacturer’s choice.
• Parts series: ISO 9457 is a multi-part standard - Part 1 addresses current pinions; a future part will cover pinions with a 20° pressure angle.

Applications and Who Uses It

This standard is practical for stakeholders involved in the design, manufacture, inspection and procurement of starter motor pinions and related components:

• Automotive OEMs specifying starter motor components to ensure spare-part interchangeability.
• Starter motor and pinion manufacturers designing metric pinions for road-vehicle engines.
• Aftermarket and replacement-part suppliers ensuring compatibility with existing starters.
• Quality, metrology and inspection labs using the base tangent length (W2) and limit dimensions for acceptance testing.
• Gear and transmission engineers referencing consistent pinion tooth geometry for system integration.

Related Standards

• ISO 701:1976 - International gear notation; symbols for geometrical data (referenced for symbols).
• Other parts of ISO 9457 - Part 1 covers currently used pinions; future parts are planned (e.g., 20° pressure angle pinions).

Keywords: ISO 9457-1:1991, starter motor pinions, metric pinions, pressure angle 14°30', interchangeability, pinion dimensions, automotive starters, gear specifications.