TM 5-4240-5501-148PSTARTERSGear Drive 12V & 120VChecking Starter MotorsIf a starting problem is encountered, check the enginethoroughly to be sure it is not the cause of startingdifficulty. It is a good practice to remove the spark plugand rotate the crankshaft by hand, to be sure it rotatesfreely. Any belt, clutch or other parasitic load will affectcranking performance.Service procedures for both the 12 volt and 120 voltstarter motors are similar and will be covered together,except where noted otherwise.A list is provided to aid in diagnosing problems for 12 voltDC and 120 volt AC systems. See page 9 and 10.CHECKING STARTER MOTOR DRIVEWhen the starter motor is activated, the pinion gearshould rise, engaging the flywheel ring gear and crankthe engine. This action can be observed by removingthe starter shield. If the starter motor drive does notreact properly, inspect the helix and pinion gear forfreeness of operation. If any sticking occurs, this mustbe corrected. Proper operation of the starter isdependent on the pinion freely moving on the helix. SeeFig. 109.Fig. 109 - Checking Starter Motor DriveDISASSEMBLING STARTER MOTOR DRIVETo remove the drive assembly for cleaning orreplacement, clamp the pinion gear in a vise havingbrass jaws, to prevent damage to the gear teeth. Thelock nut may then be removed and the starter drivedisassembled for cleaning or replacement.The pinion gear should be inspected for damaged teeth.If a sticking condition exists between the pinion gear andthe helix, the parts may be washed in a solvent such asStanasol or Varsol. If the sticking condition is notcorrected by cleaning, the complete drive assembly mustbe replaced. Individual parts of the drive assembly arenot available.ASSEMBLING STARTER MOTOR DRIVEReverse disassembly procedure for assembling. Theinterior of the shaft screw has a spline machined to thecenter; when assembling, the spline must face the end ofthe armature shaft. See Fig. 110. Torque the lock nutto 170 inch pounds (19.2 Nm). This torque has an effecton pinion travel, so proper torque should be maintained.NOTE: Do not lubricate Drive Assembly.NOTE: For starter motors equipped with nylon piniongear, page 24 and 25 contains assembly and repairinformation.Fig. 110 - Assembling Starter Motor DriveIf sticking occurs during freezing weather, spraya dry silicone spray on helix.CHECKING STARTER MOTORPERFORMANCE120 VOLT AC STARTER MOTORSA performance test of the 120 volt starter motor may bemade in the following manner.Equipment Needed1. A tachometer capable of reading 10,000 RPM.2. An ammeter capable of reading 0 to 10 amperes.31
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