Starter damage assessment

Here you will find valuable and useful workshop tips about starter damage assessments.

Important safety note The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.


Starter damage assessment: Causes and effects

Starter “pasting”

Starter “pasting” can be detected from increased noise and damaged starter pinions. In extreme cases, the motor ring gear may also be severely damaged.



“Pasting” is caused by a combination of dirt (clutch dust/abrasion, whirled-up road dust) in the clutch housing and grease on the armature shaft, the counter shaft, the steep thread and in the one-way clutch. This compound produces a paste that can no longer be lubricated.



Due to the formation of this paste, which can no longer be lubricated, the function of the starter, especially the freewheel gear and the steep thread, is impaired to such an extent that the starter pinion disengages too slowly from the engine ring gear. This results in the faults mentioned above. These can usually only be remedied by replacing the starter. 


Use only greases suitable for this application or supplied by the manufacturer. Make sure that all cover plates and sealing plugs of the clutch housing are present and properly installed. If the starter is renewed, the clutch housing should be cleaned to avoid premature "pasting".


Damage to starters with ferrite magnets

In some starter types, the copper or aluminium field windings are replaced by ferrite magnets. Broken ferrite magnets are a damage pattern that occurs frequently with this starter type. This causes the magnets to detach from the housing and break.



Impacts and/or blows cause the damage patterns mentioned above. The destroyed ferrite magnets lead to total failure of the starter. As a matter of principle, a "function test" using hammer blows or similar on the starter housing or the solenoid switch should not be performed for these starter types. Letting them drop onto the floor can also cause damage.


Engine with misfires

A misaligned ignition or injection pump can cause damage to a starter. Common damage patterns are destroyed freewheels and planetary gears as well as broken armature shafts and bearing bells.



Misfiring or an incorrectly set injection/ignition timing can cause the engine to kick back during the starting process. At this point, a force is applied to the starter against its direction of rotation. This loads the freewheel in the locking direction, which forwards the force to the housing via the armature shaft. Since the starter can only absorb these forces to a limited extent, this leads to the damage patterns mentioned above. 



The mechanical damage results in considerable noise and even total failure of the starter.


Starter overrun

Overrun starters can be identified by discolouring on the one-way clutch/pinion, traces of scuffing on the armature shaft, an ejected commutator/armature winding and/or a burnt solenoid switch coil.



Overrun starters can have technical causes or be caused by incorrect operation. A jammed ignition/start switch, short circuits in the wiring or operating the starter for too long will cause it to remain on after the engine has started. The enormous centrifugal forces destroy the winding and/or the commutator. Discolouration of the engaging relay’s coil insulation indicates a continuous current.



Destruction of the commutator and/or winding as well as overheating of the coil will lead to total failure of the starter.


Starters with oil contamination

A starter contaminated with oil can be identified by oil deposits in the bearing bell and in the starter. In extreme cases, it can also be identified immediately by an oil film or oil drops on the starter. The customer often notices this fault when the starter is performing poorly.



In most cases, oil contamination is caused by leaks in the engine. A leaking crankshaft oil seal is the main cause in particular. The escaping oil is thrown into the starter by the flywheel.



The oil that has penetrated the starter causes the carbon brushes to soften, resulting in increased abrasion. The carbon abrasion forms a conductive mass together with the oil, which leads to short circuits and contact problems. In most cases, this results in total failure.


Overloaded starters

An overloaded starter can usually be identified by discolouring on the armature, a burnt field winding and a discoloured or a burnt solenoid switch coil. These are characteristics that indicate a high thermal load.



Starters are generally designed for short-time operation only. A continuous load due to an engine that starts poorly or not at all (incorrect setting, faults in the fuel supply, ignition system, mechanical faults) leads to overheating.



The consequential damage resulting from this overheating is usually short circuits due to the insulation burning. This leads to a total failure of the starter.



Here you will find tips and remedies for specific symptoms and causes for the failure of a defective startermotor. In addition, we show you on this page how to check the charging system , such as carrying out a visual inspection before diagnosis, testing the batteries, performing the alternator test and testing with the diagnostic device. You can find more product information about starters and alternators from Hella here.

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