ELECTRICAL EQUIPMENT—Q.12which now close. Closing of the contacts short circuitsthe resistor and allows full current to flow through thefield windings. The armature now rotates under fullpower, with the pinion and engine flywheel fullyengaged. This completes the second stage.In order to avoid premature disengagement of thepinion before release of the starter button, a ball-lockingdevice is positioned between the armature shaft andpinion sleeve. This consists of the followingcomponents:Four steel balls (16) located in holes in thepinion sleeve.A locking collar (17) mounted on the pinionsleeve.The collar loading spring (18).Four recesses (39) in the armature shaft.The balls, set in holes in the pinion sleeve, areretained in position by the lock-collar, the inside bore ofwhich, has a 450 chamfer, causing the balls to bepressed inwards against the armature shaft.In the stationary position, the balls hold back the lockcollar. When the pinion moves forward to the fullyengaged position. the balls become opposite therecesses in the armature shaft sinking into them as theshaft revolves. Spring pressure pushes the collar overthe top of the balls, locking them in the recesses. Thusany backward or forward movement of the pinion sleevecan no longer occur and the pinion is securely held inthe fully engaged position as long as the starter buttonremains pressed.Releasing the starter button cuts off the solenoidcurrent. Under the combined pressure of the maincontact and plunger springs (14) and (42). the plungerreturns to its normal position. carrying with it the movingcontact plate. Thus both sets of contacts open. Withcurrent cut, the rotation speed of the armature rapidlydrops. The returning plunger pushes back the lockcollar, releasing the balls and freeing the pinion sleeve.The engine flywheel speed now rapidly over-runs thepinion speed. This action, combined with the pressureof the return spring (4) throws the pinion out of meshwith the flywheel, returning the pinion to the disengagedposition.Fig. Q.10.Any tendency of the pinion to wander forward undervibration resulting in damage to the contact andarmature assembly, is prevented by pressure of thepinion return spring (4).On rare occasions, badly worn pinion and flywheelteeth may meet face to face, preventing engagementand causing the pinion to remain stationary against theflywheel when the starter button is pressed. Specialprovision is made for overcoming this difficulty. At thecommutator end of the armature, a steel ball thrustdevice is fitted.This consists of a spring (36), guide (33), steel ball (32).and thrust-washer (30), against which the armaturepresses. The spring and ball are held in position by anend-cap (34) secured to the commutator end shield by aspring clip (29).Should a face-to-face contact occur, the armature.under the influence of the helix, will be turned slightlyand at the same time forced back against the spring:end movement of approximately 1/16 in (1,6 mm) ispermitted. When the starter button is released thearmature and pinion will come back to the normaldisengaged position, but the radial position of the pinionwill be slightly in advance of the previous position, sothat the next engagement will be made quite smoothly.In order to maintain the required tolerances, shims (28)are fitted at the commutator end.
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