Starter motor nearly catches fire

[lustyd]

I never use WD40 on anything these days. What lube? Lock oil? 3-in-1 oil, silicon spray (mast-track) lube?

Now that’s a thread of its own! You want the key clean or the lock smooth?

 

[Plum]

Fuses only prevent fires in the wire they are designed to protect. Unfortunately in your situation that doesn't help.

Plenty of people have made this mistake, usually only once. I can't think of a clever way to prevent it unfortunately other than changing to a start button (which many boats have instead of a key). On our boat we'd have to physically hold the start button in to have this issue.

I had the same starter motor issue 2 years ago. I have a starter button, no key switch, but the pinion stayed engaged with the ring gear. The starter, a gear reduction type, as many modern ones are, was being driven by the engine and started to smoke after just 2 minutes.
The overall gear ratio of electric motor to flywheel could be 60 to 1 so an engine idling at 800 rpm with a stuck starter will drive that starter at 48000rpm, that can generate a lot of heat.

 

[Juan Twothree]

I've had this happen on an inshore lifeboat. Water ingress into the engine starter panel, shorted out the start button, and kept the starter engaged.
The first we knew of it was when it tripped the main breaker, presumably because it was now acting as a generator and sending current to places it wasn't meant to go.
The RNLI have changed the design of the starter panel now

 

[Stemar]

My boat's Beta panel has a key, but it is spring-loaded to return to the neutral position from both pre-heat (held anticlockwise) and start (held clockwise); stop is a button.

I have the same panel, but the key switch stuck in the start position, By the time I'd gone 300 yards to my mooring, the starter was fried.

 

[Babylon]

I have the same panel, but the key switch stuck in the start position, By the time I'd gone 300 yards to my mooring, the starter was fried.

Would killing the 12v supply to the engine circuit (by simply flipping the isolator switch) not have disengaged the starter motor?

 

[jwilson]

I have experienced this also as I purchased a cheap generic spring loaded key switch to replace a starter button that had failed. Burned out both the starter and alternator on Yanmar. Needless to say I now have a button for cranking

Starter motor burnt out happened to me too with a genuine Yanmar keyswitch. Keyswitch replaced with another Yanmar branded one. Some years later happened again. Now changed to pushbutton start, following suggestion by Yanmar dealer.

New Yanmar YMs now come with pushbutton panels ......

 

[MikeBz]

Ours is wired so that the solenoid drops out when the alternator starts generating, so if you hold your finger on the button or it sticks the it doesn’t matter. Doesn’t stop the starter motor from spinning if the pinion fails to disengage of course.

 

[penberth3]

Would killing the 12v supply to the engine circuit (by simply flipping the isolator switch) not have disengaged the starter motor?

Well yes, but the problem is you have to realise what's happening and a stuck starter doesn't give you any clues until it's too late.