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Ignition coil overheating

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mlachak
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Ignition coil overheating

Post by mlachak » Sat Jul 16, 2016 4:25 pm

I have a 1954 Sportsman with an MBL. The electrical system was retrofitted to a 12v by a previous owner.

We have had stalling issues when we run for about an hour. This cycle time is shortened with some heavy use, like tubing, and stretches out if we baby it. I've narrowed the issue to a problem with the ignition coil overheating. In the past, when we stalled we would have to sit for quite a while before it would restart. Now, if I cool the ignition coil with water, it starts up right away. When I replace the ignition coil, it will work well, meaning no stalls, for the first few outings. After that, it's back to the old routine.

I'm trying to figure out why the ignition coil is overheating. A few other facts:

- it is a negative ground
- the latest (unused) coil I'm installing is a NAPA 12v w/ an internal resistor. The previous versions were generic brands.
- it appears as though the wire from the key ( not the ignition button ) is an 16 ( maybe 18 ) gauge wire. The others, for the generator and starter, appear to be 12.

Thoughts?

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Re: Ignition coil overheating

Post by boat_art » Sat Jul 16, 2016 5:21 pm

"- it appears as though the wire from the key ( not the ignition button ) is an 16 ( maybe 18 ) gauge wire. "
This is confusing...did you meant the start button rather than ignition button?
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mlachak
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Re: Ignition coil overheating

Post by mlachak » Sat Jul 16, 2016 5:27 pm

Yes.

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dag55
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Re: Ignition coil overheating

Post by dag55 » Sun Jul 17, 2016 12:04 pm

You need to run the coil via a resistor.
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mlachak
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Re: Ignition coil overheating

Post by mlachak » Sun Jul 17, 2016 1:13 pm

Thanks Dag55! I will look at that. Is this still the case even though the coil has an internal resistor? There are 11.81v coming into the coil (key on not running). If 11.81 is too much, what should I reduce it to? I tried to find out what the specs of the NAPA coil are....after I threw the packaging away....but haven't found anything soecific to the incoming voltage.

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Bilge Rat
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Re: Ignition coil overheating

Post by Bilge Rat » Mon Jul 18, 2016 12:55 pm

If the coil is rated as "no external resistor needed" it was meant to run without a ballast resistor in the coil primary circuit wiring. The coil will run hot as the internal resistor will still heat up. The same type of coil on my Graymarine 327 V8 is too hot to hold in your hand after a run, which is normal. Temporarily cooling with water would seem to indicate its overheating, but you may want to check the condition of the points and condenser. Points with high resistance (should normally be extremely low like 1 to 3 ohms when closed) will cause hard or no starting after a run and there have been multiple threads about Chinese made condensers causing starting problems.

Had this same problem this past weekend and determined the points had high resistance, even after replacing the coil with 2 spares. I didn't want to replace the points on the water in 1 -2 foot waves, so the dollar bill trick to clean them saved the day. Now that it's back on dry land and not pitching about, I can replace them and accurately set the gap.
Last edited by Bilge Rat on Mon Jul 18, 2016 2:00 pm, edited 1 time in total.
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Bilge Rat
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Re: Ignition coil overheating

Post by Bilge Rat » Mon Jul 18, 2016 1:58 pm

Also the 11.81 volts to the coil when not running is fine. When running and the generator/alternator is charging the battery, the voltage could go as high as 14 volts and the coil is designed to take that.

If you can bump the engine until the points are solidly closed, remove the 12 volt ignition wire connection from the distributor and check resistance of the distributor terminal to engine ground, you should see almost 0 ohms. When the points are fully open, you should see infinity or a very high meg-ohm reading. Don't touch your meter lead terminals when performing resistance measurements, as your meter will read the resistance of you and mess up your readings!
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

mlachak
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Re: Ignition coil overheating

Post by mlachak » Tue Jul 19, 2016 6:47 pm

Thanks Bilge Rat!

As I am highly resistant, I will try not to mess up the readings.

Would an issue with the points also cause stalling, or just hard starts? We have an issue starting only after it stalls due to this particular problem we are experiencing.

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Bilge Rat
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Re: Ignition coil overheating

Post by Bilge Rat » Thu Jul 21, 2016 2:29 pm

Poor contact condition of the points could cause stalling problems. Although the whole points opening and closing to generate a collapsing magnetic field in the coil to make high voltage is really a simple piece of electrical physics, it doesn't take much to disturb the event. Couple that with the coil naturally heating up as it runs and the electrical properties such as resistance and capacitance could change enough so that the points might not function well enough and it stops the engine.

It may also just be time for an old fashioned ignition tune up; new points, condenser, rotor, cap and spark plugs.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

mlachak
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Re: Ignition coil overheating

Post by mlachak » Thu Jul 21, 2016 7:55 pm

Roger....thanks bilge rat. We'll give it a go and see what happens!

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