Starter - Bosch Porsche 944 I

DESCRIPTION

Starter is a brush type, series wound electric motor with an overrunning clutch. Field frame is enclosed by commutator end frame and drive bushing and carries pole shoes and field coils. A spline armature shaft drive end carries drive assembly. Armature shaft is supported at both ends by sintered bronze bushings.

BOSCH STARTER APPLICATION (1)

LOAD TEST

Ensure battery is fully charged. Battery cables and connections should be in good condition. Connect a voltmeter, ammeter and tachometer to vehicle. Disconnect ignition primary circuit, so engine will not start. Turn all accessories off. Engage starter with ignition switch. Voltmeter and ammeter reading, and starter RPM should be within specification.

NO LOAD TEST

With starter on test bench, take readings of starter current, voltage and RPM. Readings should be within specification.

Removal & Installation

1. Follow manufacturer's precautions prior to working on vehicle electrical system. Remove negative battery cable. Raise vehicle on hoist if necessary.
2. Mark starter wiring for reassembly. Support starter and remove starter mounting bolts. Remove starter from vehicle. To install, reverse removal procedure.

DISASSEMBLY

1. Clamp starter in vise. Remove nut and washer from solenoid main terminal connection. Remove solenoid retaining screws and unhook solenoid plunger.
2. Remove screws and end cap with rubber seal from commutator end housing. Wipe grease from armature shaft and remove "C" clip with shims.
3. Remove bolts or nuts from studs and lift off commutator end housing. Lift springs clear of brushes and slide brushes from holders. Remove brush plate from housing.
4. Separate drive end housing and armature assembly from yoke by tapping apart. Remove armature assembly from drive end housing while at the same time uncoupling actuating arm.
5. To remove actuating arm, remove rubber insert from drive end housing. Remove pivot arm screw and nut and extract actuating arm.
6. To remove drive pinion assembly from armature shaft, separate thrust collar from over "C" clip. Remove "C" clip from its groove and drive pinion assembly off armature shaft.

Exploded View of Typical Bosch Starter. Scheme 1

CLEANING & INSPECTION

Clean all parts with cleaning agent. Inspect for wear or damage. Apply thin coat of oil to running surfaces.

Brushes & Springs

1. Check brush spring pressure with spring scale. Check brushes for minimum length and freedom of movement in holders.
2. If necessary, replace brushes by cutting old brush leads midway between connection and old brush. Solder new brushes to original leads.

Armature

1. Check commutator-to-shaft (or core) for short circuit with 110 volt AC test light. Test light should not light (a slight glowing is okay).
2. Using an armature growler, check armature coils for short circuit between windings. Check commutator for pits, burns or rough surface.
3. If out-of-round exceeds .002" (.05 mm), or grooves or burned spots cannot be removed with fine crocus cloth, turn commutator. Undercut insulation between commutator bars to a maximum depth of .016" (.40 mm).

Note. Never use emery cloth or a file on commutator. Turn on a lathe only.

Bushings

1. Self-lubricating bushings should be replaced only when worn or damaged. Force out bushings with mandrel.
2. Clean hole and remove burrs. Before pressing new bushing into place, soak it in lubricant for at least 30 minutes.

Drive Assembly

Replace drive when damaged or teeth are worn. See DISASSEMBLY in this article.

Solenoid Plunger (Armature)

Plunger must move in and out of solenoid body when disconnected from pinion drive lever. If corroded, clean thoroughly before proceeding with tests.

Solenoid Pull-In Coil

Connect jumper wires between a 12 volt battery and solenoid. (Scheme 2) Armature should pull in and return when current is removed.

Typical Connections for Pull-In Test. Scheme 2

Hold-In Coil

Connect jumper wires between a 12 volt battery and solenoid, while pressing armature into solenoid by hand. (Scheme 3) Armature should remain held in. Disconnect jumper terminal No. 50 and armature should immediately return to its outer position.

Typical Connections for Hold-In Test. Scheme 3

Note. Do not attempt to repair solenoid. If either test is unsatisfactory, install new solenoid.

REASSEMBLY

1. Slide drive pinion assembly and thrust washer onto armature shaft. Install "C" clip into groove in armature shaft and pull thrust washer up over clip.
2. Align fork in drive end housing and insert pivot pin. Slide armature assembly into drive end housing, coupling shift fork onto drive pinion flange.
3. Install rubber insert in drive end housing. Guide yoke assembly over armature while aligning notch with rubber insert. Tap yoke into full contact with drive end housing.
4. Install brush assembly. On models with through bolts, cut-outs in brush plate slide over through bolts. On models with screws, brush plate cut-outs align with loops in field windings.
5. Plates are properly positioned when screws are installed in commutator end housing. Install brushes and springs. Ensure field winding brush leads do not contact yoke.
6. Slide commutator end housing into position and secure with nuts and washers or screws, as necessary. Install drive end housing. Install shims onto armature shaft at commutator end to eliminate end play. Install "C" clip in groove.
7. Install bearing cap seal on commutator end housing. Lubricate end of armature shaft with lithium-based grease and install bearing cap. Lubricate plunger hook and place in position over shift fork in drive end housing.
8. Install solenoid body with return spring properly positioned. Tighten retaining screws and field connections.

SPECIFICATIONS

STARTER SPECIFICATIONS

BRUSH SPECIFICATIONS

Poses Online

See also:
• DISASSEMBLY