Coil questions

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Mark44
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Coil questions

#1

Post by Mark44 » Mon May 14, 2012 6:33 am

This should be an easy one for you experts. I've been meaning to check the points gap and set the timing on my Pan with a '55 motor. Following the directions in Palmer's book and in the Panhead service manual, I couldn't get the test lamp to go off even with the points open. After doing some diagnosis, I determined that the coil was shorting to ground. The coil is the old type square coil, and I get continuity between the front terminal (that goes to the timer) and ground, which I believe is why I couldn't get the test lamp to go off.

Does my diagnosis sound about right?

If so, I will be replacing the coil, which brings me to question #2. JP Cyles has three coils, ranging in price from $39.99 (round style) to $54.99 (square, chrome) to $79.99 (VTwin replica). Do any of you have any recommendations of the best one I should get? My biggest consideration is that the thing works right and isn't junk. The only American-made coil they offer at JP is for '65 and up.

Thanks,
Mark



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Re: Coil questions

#2

Post by 1950Panhead » Mon May 14, 2012 12:22 pm

If you have continuity between either terminal (points, battery) and ground replace the coil.
Disconnect both wires before running test.
I've had good luck with my vtwin coil.
Connect battery to +, points to -, connecting backwards shortens coil life.
Jerry

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Re: Coil questions

#3

Post by BlainesGarage » Mon May 14, 2012 6:16 pm

Mark,
If it ran, the coil is ok. Not sure how the palmer
book explains it, but if one lead of your test light is attached
to one small wire of the coil and the other lead
is attached to the other small wire of the coil,
ignition switch turned ON, the light will should
be on most of the time but just as it goes off, (points open),
is what you're looking for.

I like having the points wire off of the coil and using
the continuity/diode test function on my meter
as it has an audible tone, so i can keep my eye on the
mark and 'listen' to the points.

Blaine...

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Re: Coil questions

#4

Post by Mark44 » Mon May 14, 2012 6:35 pm

Thanks, Blaine and 1950Panhead.

With both primary circuit wires disconnected from the coil, and testing each terminal, I'm not getting continuity to ground, so the coil seems fine. The way both Palmer and the the service manual describe the test, they bypass the ignition switch completely, and connect one lead of the test lamp to battery + and the other lead to the wire terminal inside the timer. The light should be on when the points are closed (it is), and should go off when the points are open (it doesn't). So it looks like I have some wire that's grounding upstream of the coil. I'll check the circuit board underneath the coil and see if there is something amiss.

The bike was running pretty well before, but was a little hard to start, which is why I wanted to check the points and timing. The only things I've touched to this point are the points and coil. It seems odd that all of a sudden I have a short.

Anyway, thanks again for the advice.
Mark

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Re: Coil questions

#5

Post by BlainesGarage » Tue May 15, 2012 2:07 am

Mark,
good news. you don't have a short.

any other items that are connected to the ignition feed circuit (oil light, neutral light, generator light)
will 'appear' as a short to ground, but are mearly a 'path' to ground for your test light, through the coil,
then through the bulbs. you might notice a brighter lamp with the points closed, but, yeah...

you need to test it with the ignition on, if you are checking it like that. light will be on with the points
closed, and off with points open.

set the points to .022", grease the lobe lightly, bring the timing mark up in the hole, if you go past, don't back up,
go around again. connect your test light, ignition ON, and while rotating the timer from full retard to full advance,
the light should just go out as the timer just reaches full advance(all the way counter-clockwise) adjust as needed.

Blaine...

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Re: Coil questions

#6

Post by Mark44 » Tue May 15, 2012 8:15 pm

BlainesGarage wrote:Mark,
any other items that are connected to the ignition feed circuit (oil light, neutral light, generator light)
will 'appear' as a short to ground, but are mearly a 'path' to ground for your test light, through the coil,
then through the bulbs. you might notice a brighter lamp with the points closed, but, yeah...
Yes, I did notice a change in brightness in the test light.

I'll give it a shot with the ignition on. I wonder why this information isn't in the service manual or the Palmer book.
Thanks again!
Mark

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Re: Coil questions

#7

Post by awander » Wed May 16, 2012 5:58 am

You might do better connecting the test light across the points(or, which is the same thing, connecting it between ground and the coil terminal that is wired to the timer).

Then the light will be OFF as long as the points are closed, and will go ON when the points open.

Either way, the ignition needs to be ON.

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