How does the Bendix drive engage the flywheel when starting?

When the starting button is pressed, the battery powers the electric motor, spinning the armature rapidly. This causes gear (A) to travel along the coarse-threaded sleeve (B) toward the motor and mesh with gear (D) on the flywheel. Spring (C) connects sleeve (B) to the armature shaft, providing flexibility and preventing too sudden engagement.

How does the Bendix gear disengage after the engine starts?

When the engine starts under its own power and the starting button is released, the small inertia gear (A) is thrown out of mesh with the flywheel gear (D), and the starting motor comes to rest.

What is the difference between outboard and inboard type Bendix drives?

When gear (A) moves away from the starting motor to mesh with the flywheel gear (Fig. 2), it is the "outboard type." When gear (A) travels toward the starting motor (Fig. 4), it is the "inboard type."

What vehicle is used as the example in Fig. 4?

Fig. 4 shows the Bendix drive on the armature shaft of a starting motor using a King car as an example.

What keeps gear (A) turning with the armature once engaged?

As soon as gear (A) is fully engaged with flywheel gear (D), it comes up against a stop and is locked firmly to sleeve (B), rotating with the starting motor armature shaft so the motor can crank the engine.

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Bendix Drive Starter Construction & Operation - Dyke's Manual Page (Fig. 4)

Manual page on Bendix starter drive construction with a labeled cutaway figure of the drive on the armature shaft

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Manual page describing Bendix starter drive construction with a labeled cutaway figure of the drive on the armature shaft.

AI caption September 2014 · Photo 154 of 332

This is a scanned page from an early automotive reference manual (apparently Dyke's Automobile Encyclopedia, based on the upload filename) explaining the construction and operation of the Bendix automatic gear shift used in starter motors. The page includes a labeled cutaway illustration (Fig. 4) of a Bendix drive mounted on the armature shaft of a starting motor, using a King car as an example, with callouts for the starting button, starting switch, oil cup, starting motor, and lettered components A through E. The text explains the operating sequence: pressing the starting button connects the storage battery to the electric motor; the armature spins, causing gear (A) to travel along the coarse-threaded sleeve (B) and mesh with flywheel gear (D); spring (C) cushions engagement. Once engaged, gear (A) locks to the sleeve and cranks the engine. When the engine starts and the button is released, inertia throws gear (A) out of mesh. A note distinguishes the alternate spring arrangement shown in Fig. 2 (page 319), and a final paragraph explains the difference between "outboard type" (gear moves away from the motor) and "inboard type" (gear moves toward the motor) Bendix drives.

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Frequently asked questions

How does the Bendix drive engage the flywheel when starting?: When the starting button is pressed, the battery powers the electric motor, spinning the armature rapidly. This causes gear (A) to travel along the coarse-threaded sleeve (B) toward the motor and mesh with gear (D) on the flywheel. Spring (C) connects sleeve (B) to the armature shaft, providing flexibility and preventing too sudden engagement.
How does the Bendix gear disengage after the engine starts?: When the engine starts under its own power and the starting button is released, the small inertia gear (A) is thrown out of mesh with the flywheel gear (D), and the starting motor comes to rest.
What is the difference between outboard and inboard type Bendix drives?: When gear (A) moves away from the starting motor to mesh with the flywheel gear (Fig. 2), it is the "outboard type." When gear (A) travels toward the starting motor (Fig. 4), it is the "inboard type."
What vehicle is used as the example in Fig. 4?: Fig. 4 shows the Bendix drive on the armature shaft of a starting motor using a King car as an example.
What keeps gear (A) turning with the armature once engaged?: As soon as gear (A) is fully engaged with flywheel gear (D), it comes up against a stop and is locked firmly to sleeve (B), rotating with the starting motor armature shaft so the motor can crank the engine.