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The scope of this document is to provide uniform guidelines for the application of starter motor pinions and ring gears. SAE J543 contains guidelines for the use of diametral pitch gearing. The pinion data shown are based on the Fellows stub tooth system. Refer to ISO 8123, ISO 9457-1, and ISO 9457-2 for module gearing, and corresponding metric dimensions.

The purpose of this SAE Recommended Practice is to provide standardized dimensions for mounting starting motors. (See Figures 1 through 4.) It is recommended that a full register diameter having a minimum depth of 2.54 mm (0.100 in) be provided in the flywheel housing to insure proper control of gear center distance and clearance between pitch diameters. The clearance between the starting motor pilot diameter and the register diameter in the flywheel housing should be 0.03 mm (0.001 in) minimum to 0.25 mm (0.010 in) maximum. Text noted with an asterisk in Figures 1, 2, and 3, should not exceed root radius of pinion in order to provide clearance for the flywheel. The face of the starting motor mounting flange should be relieved at its junction with the pilot diameter to avoid mounting interference with flywheel housing. For backlash allowance between the pinion and ring gear refer to SAE J543. Dimensional units—millimeter (inch)