Analyzing Starting Motor Failure

Topic: Analyze starter failure prior to installing a replacement starter.

   Starter damage often results from attempting to crank with low battery (cranking) voltage on the electric starter.  Basically, the same forces that make welding possible, occur inside the starter. A dash board volt meter will not tell you if your about to wipe out a starter. The only valid test is to load test the battery and associated wiring, before you hit the starter switch. Engine ring gear damage may result in this situation, as well.

One problem almost unique to boats is water flooding of the starter. A starter that has been submerged, needs to be torn down, cleaned,  and the solenoid replaced. Other than submersion, there are four main reasons for starter failure.

1.) Wear out during normal starter life (2000 to 5000 hours).

Wear out refers to normal or expected starter life . The starter needs replacement because:

·the commutator brushes are too short.

·the nose housing bearings are worn (sloppy).

·or the solenoid contacts are no longer a good switch to connect the battery to the starter.

The result is a starter that no longer cranks or might crank sluggishly. In this situation, the starter and starter solenoid show no real visual signs of failure. The drive gear is NOT broken or blue from heat, the armature shaft is NOT blue, there are no "hot" spots sometimes easily visible on a painted housing.

2.)  Starter stays engaged with ring gear during start-up.

Several things may cause starters to stay in mesh with the engine ring gear during start-up. Indications that this has occurred include:

· Blue, badly worn, or broken starter drive gear; or worn bearing.

· Excessive wear in the armature shaft bearing of the nose housing.

· Armature shaft that is locked up and cannot be rotated.

· "Hot" spots in the paint on the brush end of the starter.

·Solenoid coils are open, shorted, or smell burnt.

If the above symptoms are observed, the starter is not usually at fault. Check for one of the following problems:

·Stuck or sticking dash mounted start switch (most probable).

·Stuck or sticking solenoid contacts (check battery). ·Stuck or sticking starter relay (if applicable).

·Failure of the wiring harness, battery positive-to-start circuit, anywhere between the start switch and the starter solenoid. This includes connectors. Look for contamination shorting contacts inside a connector shell.

· Loose and/or incorrectly positioned wiring on the solenoid. This may cause the solenoid to engage the starter.

If any of the symptoms above are noted, but the exact cause cannot be identified, replace the start switch.

3.)  Starter attempts to reengage the ring gear after start-up.

A starter that is replaced because the drive attempted to re-engage with a running engine ring gear shows one or more drive teeth "milled" or chewed up on the leading edge. This fault is usually caused by operator error or an intermittent faulty "start" signal to the starter from a start switch, start relay, or harness fault.

4.)   Damage from low voltage on the starter motor.

The results of low voltage on the starting motor while cranking can be:

·Sluggish cranking.

· No cranking or maybe only a "click" .

·Starter can be heard to "chatter" or pulse the drive in and out of the ring gear at a rapid rate.

· Solenoid gets hot and may even weld the contacts closed so that the starter tries to crank continuously, or may run (operate) without cranking the engine. (See the illustrations.) The solenoid contacts show a burnt or "smoked" spot (and sometimes, melted) while the rest of the contact area shows previous starts were normal.

· One or more (but not all) starter drive teeth show case crushing of the hardened tooth surface.

· Badly chipped, or broken engine ring gear teeth.

·Bent armature shaft at drive end caused by engine "rock-back.

·Twisted armature drive splines that cause the drive to "stick" on the armature shaft.


Warning: Marine Starters are of a special design. If they are not marine grade or they have been rebuilt or reassembled incorrectly, the starter can cause an explosion. Do not exchange marine and automotive parts. If you rebuild a starter, you become the manufacturer and therefore liable for any damages caused by your actions.


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