Cause of Starter Wiring Fire?

[lavida]

Started my 1973 120hp ford lehman engine first time in 4 months. After 5 minutes the wiring to the starter and solenoid heated up and burned off the wiring insulation. Turned off engine and noticed smoke coming from my battery selector switch in DC Panel as well!

Any ideas where to start to debug?

Thanks
LaVida

 

[MYTraveler]

At the risk of stating the obvious, short somewhere. I would begin with the starter motor. Probably any electric motor rebuilder could easily check/diagnose/rebuild for a reasonable price.

After reading your post a little more carefully, I am not so sure. Did the engine start normally or were you cranking for 5 minutes. Starter motor would not be energized after starting unless the solenoid was bad. So maybe check that first. Or take them both to a motor shop.

 

[lavida]

MYTraveler: the engine started right away. I did not overload the wiring with excessive time turning it over. The odd thing... after I turned off the SB engine, the starter kept attempting to start the engine, but did not have enough power so was making that sick noise when you try to start a car engine and the battery is almost dead. The lehman was actually turning over 1/4 turn and stopping and attempting to start again. Repeated half dozen times until I hit isolator switch in engine room.

I can check starter for short ( I used to work in an armature rewind company years ago) and check the battery selector switch for short as well. Any chance this could be a faulty regulator OR power surge coming from say a charger or alternator or?

BTW I have twin Ford Lehmans on board. The Port engine ran fine without any burning wire issues!

 

[FlyWright]

Sounds like a bad solenoid keeping the starter engaged, turning it into a generator. What did your ammeter read after start?

After shutting down the engine, it was still engaged. Did you have to turn the start battery switch to off to stop it?

 

[lavida]

FlyWright: I did not check my ammeter settings unfortunately. Was doing my walk around at stern to check water circ and exhaust. Then upon return to salon heard sound from engine that was not quite right - then discover wires burning. I used salon mounted engine kill switches to stop engines. Then went into engine room and used batt isolator switches to remove power to starter/alternator. Have not dared power 12 volt up again. Value my wooden boat too much for fire to consume her (sic). Replacing the starter wiring and replacing the solenoid is easy. The main panel batt iso switch may be a bitch to find - original 1973 part.

 

[Bluto]

Sounds like a bad solenoid keeping the starter engaged, turning it into a generator. What did your ammeter read after start?

After shutting down the engine, it was still engaged. Did you have to turn the start battery switch to off to stop it?

Your mention of the solenoid sticking was also my first impression.
The starter will generate considerable juice spun up by an idling engine.
My guess is the solenoid, wiring and starter will all need to be replaced.

I've seen motorcycles do this, minus the fire. Smoke was released, though.

 

[Brent Hodges]

Your starter solenoid stuck, leaving the starter contacts engaged. What ends up being pretty much a dead short. Cables melted, switch contacts melted, etc. I saw one (actually on a Lehman 120 in a wooden 42 GB) while I was sitting in the er between the engines. Pretty exciting. Pull the starter and have it gone through, including new solenoid and whatever else it needs. Of course you'll have to replace all cabling and switches that were damaged. Don't take any shortcuts. Hire a professional if you're not sure of you skills in this area. Boats burn down from such things!

 

[lavida]

Thanks Brent. I suspected as much but appreciate your confirmation. I will be replacing solenoid, starter (after inspection), batt switch and the burned wiring. Will also replace solenoid on the other engine before it fails - since they are same vintage.

 

[FF]

No need for the solenoid to be the culprit , the Bendex can fail and cause a no starter cut out condition.

The flywheel teeth spin the starter at amazing speeds making high voltage DC.

 

[Ski in NC]

The starter has an overun clutch to keep engine from overspeeding starter should it not disengage.

The OP's problem could be the starter bendix solenoid sticking, the local relay sticking, or even the helm starter button or keyswitch sticking. Any one of those could cause what happened. Most likely the starter bendix solenoid, as it carries the most amps and has the best chance of contacts welding.

Once fixed, try several starter cranks with stop button pushed, make sure starter stops after each one.

Also a good hint to watch voltmeter after a start. If starter hangs, volts will stay low due to the current drain.

 

[Chrisjs]

Just curious .... do starter circuits usually have a fuse/circuit breaker .. and if so, why did it not protect the system?? Not sure whether I have a fuse/breaker myself, or just the dedicated power switch near the engine!! Will check after hearing responses.

 

[Ski in NC]

Usually no fuse. If starter hangs up after engine starts, it is running with no load. In that state it is drawing enough amps to eventually burn up, but still less amps than while actually cranking the engine. So if fuse does not blow while cranking, it would not blow in this instance.

 

[Chrisjs]

Thanks, Ski

 

[lavida]

The starter has an overun clutch to keep engine from overspeeding starter should it not disengage.

Reviewing the incident I do not believe the cause was an overspeeding starter.
Once I stopped engines with helm kill switch the starter stopped. The melting wires and the attempted engine restart indicates the problem is most likely a failed solenoid. BTW in this 1973 Ford Lehman config the solenoid is mounted about 8" inches away from starter.

Thanks Ski!

 

[rwidman]

Just curious .... do starter circuits usually have a fuse/circuit breaker .. .

No they do not.

 

[OFB]

Just a thought. From my experience with a stuck solenoid hitting the solenoid with a screw driver or such can disengage the solenoid. Keep the ER floors off < grin > . It can be a way of confirming if it is the issue.

YMMV.

 

[FlyWright]

Get a remote start switch for troubleshooting and ER starts.

 

[lavida]

A true mechanic

Just a thought. From my experience with a stuck solenoid hitting the solenoid with a screw driver or such can disengage the solenoid. Keep the ER floors off < grin > . It can be a way of confirming if it is the issue.

YMMV.

Years ago I was in plant engineering. Soon discovered the best millwrights had a wide selection of hammers for exactly this approach.

 

[RT Firefly]

Greetings,
Mr. l. Ah yes, but those millwrights knew what to hit, how hard and how many times. THAT only comes with experience.