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Type :
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Starter Motor
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Specification :
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24v 4.5KW
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Number of feet :
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10T
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Brand :
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NUOJIN
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Number :
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111257,111760,US857
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Quality :
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refurbish
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Delivery time :
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30 days
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The installation of the Mercedes-Benz 24V starter motor must follow the process of safe power-off → cleaning and positioning → standardized tightening → electrical connection → test and verification. The core lies in tightening bolts to the original factory torque specifications, ensuring proper meshing between the overrunning clutch and flywheel ring gear, and securing electrical connections without looseness. It is adapted to the 24V systems of commercial/heavy-duty vehicles to ensure smooth starting without malfunctions.
Park the vehicle on a level surface, engage the parking brake, and shift into neutral. Turn off the ignition switch and disconnect the negative terminal of the 24V battery (for hybrid/high-voltage models, additional high-voltage power-off procedures must be performed) to prevent short circuits.
Prepare socket wrenches (commonly used 13/16/18mm), a torque wrench, flathead/Phillips screwdrivers, and terminal crimpers. The new starter motor must match the vehicle model (e.g., OM471/OM473 series). Inspect the overrunning clutch gear, solenoid switch, and carbon brushes for no damage, and ensure the overrunning clutch rotates smoothly without jamming.
Thoroughly clean oil stains, iron filings, and rust from the mounting surface of the engine flywheel housing and the starter motor flange. Check the flywheel ring gear for worn or chipped teeth; replace it if necessary. Apply a thin coat of special high-temperature grease to the overrunning clutch guide bearing and shift fork.
If replacing the old starter motor due to worn carbon brushes or a faulty solenoid switch, verify that the power, mounting holes, and terminal definitions of the new starter motor match the original specifications.
Align the starter motor flange with the mounting holes on the flywheel housing to ensure the overrunning clutch gear faces the flywheel ring gear without interference. Insert 2–3 positioning bolts (do not fully tighten) and adjust the starter motor position to initially align the overrunning clutch with the ring gear.
Pre-tighten all mounting bolts (usually 2–4) in a diagonal/cross pattern, then use a torque wrench to tighten them to the original factory specifications: 35–45 N·m for M10 bolts and 60–70 N·m for M12 bolts (refer to the vehicle-specific service manual for exact values). Do not use an impact wrench to avoid thread stretching or flange deformation.
Check that the starter motor is securely fastened without axial/radial play, and ensure the gap between the overrunning clutch gear and the ring gear meets specifications (typically 0.5–1.5 mm).
First, connect the solenoid switch control wire plug (small terminal) and ensure the locking clip is fully engaged. Then connect the 24V power cable (large terminal), tighten the nut with terminal crimpers to 8–12 N·m to prevent looseness and overheating.
Use cable ties to secure the power/control wires to the engine wiring harness bracket, avoiding interference with rotating components and maintaining a distance of ≥50 mm from high-temperature parts (e.g., exhaust manifold).
Install the starter motor dust cover/guard to fully cover the overrunning clutch and solenoid switch, preventing dust and moisture from entering. Connect the ground wire (if equipped with an independent ground terminal) and tighten it to 10–15 N·m to ensure proper circuit conduction.
Reconnect the negative battery terminal, turn on the ignition switch, and ensure no warning lights illuminate on the instrument cluster. Measure the voltage at the solenoid switch terminal: ≥22.5 V at idle and ≥20 V during starting to prevent weak starting due to low voltage.
Briefly press the start button to verify smooth operation of the starter motor without abnormal noise, normal engagement/disengagement of the overrunning clutch gear with the ring gear, and no gear scraping/jamming. Limit continuous starting to ≤5 seconds with intervals of ≥15 seconds to avoid overheating.
Start the engine to observe normal starting speed without drag. Ensure no abnormal noise from the starter motor at idle and complete retraction of the overrunning clutch after engine shutdown.
If the starter motor fails to operate, check the power terminal/control wire plug connections. For abnormal noise, inspect the gap between the overrunning clutch and ring gear, bolt torque, and lubrication status.
These core precautions cover safety, component compatibility, installation accuracy, electrical specifications, commissioning, and special vehicle requirements. Strict adherence prevents starting failures, component damage, and safety risks.
Always turn off the ignition switch and disconnect the negative terminal of the 24V battery first. For hybrid/high-voltage models, additional high-voltage power-off and voltage verification procedures must be performed. Reconfirm the ignition switch is in the OFF position before connecting wires to prevent short circuits that could damage the ECU or cause arcing.
Never touch the starter motor power terminals with tools during wiring to avoid personal injury or component ablation from high-current discharge.
The new starter motor model and power rating must match the engine (e.g., models compatible with OM471/OM473 series). Ensure the overrunning clutch gear, solenoid switch, and carbon brushes are undamaged; the overrunning clutch rotates smoothly, achieves reliable one-way locking, and operates without jamming or abnormal noise.
Inspect the flywheel ring gear for chipped or severely worn teeth (replace if tooth thickness wear exceeds 1/3). Severe wear will cause gear scraping and weak starting.
Thoroughly clean oil, iron filings, and rust from the engine flywheel housing mounting surface and starter motor flange to ensure gap-free contact, preventing vibration and bolt loosening.
Apply a thin coat of special high-temperature grease only to the overrunning clutch guide bearing and shift fork. Never apply grease to the overrunning clutch gear or flywheel ring gear, as this attracts contaminants leading to slipping or abnormal noise.
References：
The content is derived primarily from official Mercedes-Benz technical documents, supplemented by industry universal standards and summarized maintenance practices.
Safety and Pre-installation: The power-off sequence, flywheel ring gear inspection, and lubrication restrictions are all derived from the "Preparation Work" chapter of Mercedes-Benz official service manuals. The high-voltage power-off procedures for hybrid models refer to the High-Voltage Safety Manual for Mercedes-Benz hybrid vehicles.
Installation Accuracy Control: The diagonal bolt tightening sequence, torque values, and the 0.5–1.5 mm gap between the overrunning clutch and ring gear correspond to the official 1001TW torque specifications and starter motor installation positioning requirements.
Electrical Connections: The priority of control wire connection and the 8–12 N·m torque for power terminals are specified in Mercedes-Benz electrical system installation standards and starter motor terminal technical requirements.
Commissioning and Troubleshooting: The no-load/load test standards and voltage thresholds (≥22.5 V at idle, ≥20 V during starting) are referenced from Mercedes-Benz starter motor performance test specifications and official diagnostic procedures.
Special Vehicle Adaptation: Additional steps for AMT/hybrid models are sourced from Mercedes-Benz TSBs and Star Diagnosis adaptation operation manuals.
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