More starter woe

[pcatterall]

Got my second new starter in 2 months. Fitted it today, all was well, tried it several times... dead chuffed at last a working boat.
Just doing sme other jobs when the starter began spinning ( but not engaging) of its own accord, had to switch off batteries to stop it, disconnected ign lead to solonoid thing that power was getting to there but still spinning. Disconnected main positive cable and flashed the solonoid with the ign, usual click and no spinning when I reconnected main cable. Left it for 30mins and it started spinning again.
On checking I found that some power was getting to the starter via the main lead ( my battery dropped from 12.5 volts to 12 volts every time I connected this lead)
Took the starter out ( swine of a job even though I am now an expert) and had the same result, some sort of short inside the 'new' starter. So the starter has gone back whence it came and the saga continues.
Any ideas how this short would be occuring? The solonoid is internal.
Regards

 

[William_H]

That is quite amazing.Presumably your previous starter worries were for a different fault.
Some starters apply DC power to the motor. The rapid acceleration of the motor causes the pinion gear to slide along the shaft on a spiral spline causing it to engage in the ring gear and so turn the engine.
Now a very small leakage across the solenoid could conceivably start the starter slowly turning. If the acceleration is not great the pinion will remain disengaged.

The other type of solenoid both moves the pinion into the ring gear and makes an electrical contact when the pinion has moved. Again any leakage across the contacts could have the starter spinning without being engaged. Either way the leakage can only come from dirt or corrosion in the box containing the contacts or on the outside of the terminals. I think you are right to take the starter back to the man and explain the problem. olewill

 

[pcatterall]

The previous starter was completly drowned so had to be replaced. The mystery spinning was quite rapid but without the power to engage the teeth. The 'short' was enough to drop my battery bank half a volt but I was unable to measure the current. The auto electrician scratched his head a bit and said he had not seen that fault before!! This is a reconned job so maybee there was a fault in its assembly. I did find some bits of fresh but ground up rubbery stuff where the shaft exits the unit, possibly they were from some insulation that had got trapped inside.
Another of lifes mysteries!!

 

[PCUK]

Maybe solenoid was engagaing the electrical contact without moving the drive gear into the ring-gear. Broken return spring possibly. In any case, severe pain to the supplier when the hospital removes it from his orifice!