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Coils leaking oil
#822503 09/06/20 12:17 am
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I left the ignition switch on by mistake and the coil got hot and started leaking oil. After it cooled down I started the engine and it ran ok. Has anyone seen this before? Should I replace the coil? Both coils have 17M12,45221A AND 15-71. The bike is a 1971 so I think they are original. Thanks

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Re: Coils leaking oil
RUSS TILLEY #822511 09/06/20 2:04 am
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I would!

Re: Coils leaking oil
Danam #822522 09/06/20 5:13 am
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when the coil is dwelled the primary side of the coil is an electromagnet .
With the ignition left on
the coil that was connected to a resting closed set of points ... overheated .

the oil is insulation and coolant .
The coil may work , or may continue to work ...or except when over-heated .
how much oil leaked out . ?

Lucas coils are pretty robust ... it could last even with the lose of a ittle oil
but at this point ... the coil has lost reliability .

Re: Coils leaking oil
RUSS TILLEY #822547 09/06/20 1:35 pm
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Thanks, I will look for a new set of coils.

Re: Coils leaking oil
RUSS TILLEY #822572 09/06/20 5:42 pm
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Fit 2 new coils, keep the old good one as a spare, chuck the leaky coil.

Re: Coils leaking oil
RUSS TILLEY #822656 09/07/20 5:31 am
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The damage may not be visibly evident, winding insulation may be compromised.

Another good reason for fitting EI

Last edited by NickL; 09/07/20 5:32 am.
Re: Coils leaking oil
RUSS TILLEY #822676 09/07/20 12:40 pm
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Coils on OIF twins are extreemly easy to swap (unless your seat is loaded up with camping luggage) So If it was my money I'd keep a spare under the seat in the tool tray and run the current ones until you have a problem, Had it been the pre OIF, their mounting is less roadside repair friendly and I'd just buy 2x new PVL coils.

The red topped wassel coils are ok (I've just fitted a 15yr old pair to the Thunderbolt project which worked when last used), the no name ones are sketchy as hell, I had a pair.... One was fine..... One failed after a few hundred miles.


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Re: Coils leaking oil
RUSS TILLEY #822699 09/07/20 4:45 pm
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Found both coils have leaked oil. CBS lists Lucas replacement coils at 37.95 each and Cycle Craft (Taiwan) at 26.95. Any thoughts if the Lucas is worth the difference in price?

Re: Coils leaking oil
RUSS TILLEY #822706 09/07/20 5:49 pm
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After using lots of parts made in Taiwan in my English bikes my opinion about them is positive. These parts were reliable and well made, so I believe Taiwan's coils should be good enough to use in our bikes.

Re: Coils leaking oil
RUSS TILLEY #822711 09/07/20 6:01 pm
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Once they develop a leak, no matter how small, they are junk


GrandPaul (does not use emoticons)
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Too many bikes to list, mostly Triumph & Norton, a BSA, & some Japanese
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Re: Coils leaking oil
RUSS TILLEY #822719 09/07/20 6:43 pm
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Originally Posted by RUSS TILLEY
Found both coils have leaked oil. CBS lists Lucas replacement coils at 37.95 each and Cycle Craft (Taiwan) at 26.95. Any thoughts if the Lucas is worth the difference in price?

The trade name Lucas has been licensed by Wassell Ltd in the UK. Wassell likely uses the same sources in Asia for manufacturing much of their "Lucas" components as Emgo. Some of the items are absolutely identical (like Lucas headlight switches vs Emgo headlight switches). One would hope that by charging a bit extra for their Lucas branded items that Wassell would demand extra quality from their manufacturers. But don't count on that.To get a truly higher quality coil get German made PVL coils. They are a good bit more expensive then the new Lucas coils (which in my mind are about the same as Emgo or Cyclecraft coils). However the cheapo ones seem to work pretty well.


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Re: Coils leaking oil
RUSS TILLEY #822747 09/07/20 9:45 pm
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The oil in the coil housing is an insulator, but its only actual purpose is to provide a thermal path to the outside world. The coil doesn't make use of the electrical insulation property of the oil in order to function (unlike the insulation on the wires, which it does need), only to keep it from overheating. This means a little oil leaking out isn't an issue in itself. However, now that it has forced its way out of the formerly-sealed can, more oil can leak unless that path is located and sealed.

Where there might be a problem is if the heat due to the current having run through the coil for two hours[*] continuously, rather than only ~half the time when the engine is running, caused insulation on the wires to crack. However, that is unlikely since the remaining oil still managed to carry away a lot of the heat. So, the decision isn't a simple as buying new coils. You have to decide between the estimated future reliability of an original made-in-England Lucas coil that was hot for a period of time and that leaked some small amount of fluid (nb. I assume the leak was small; if not, let us know), and the hoped-for reliability of an aftermarket coil made overseas.

[*]Your coils are 4 ohms each and are in parallel so they each drew 3 amps from your 12 V battery. This dissipated 36 W ea. that the oil needed to carry to the can and from there to the air. If it was a 12 Amp-hr. battery that heating went on for ~2 hrs. before the battery was depleted.

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Re: Coils leaking oil
RUSS TILLEY #822785 09/08/20 6:36 am
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The 17M12 coils from '72 that I have on the racer (which lay horizontal) still work fine. They have a screw on the top that can be opened to add oil if needed but have never had to do so.

Re: Coils leaking oil
DMadigan #822844 09/08/20 5:46 pm
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I seen the screw on top of the coil but did not know what it was for. What type of oil would go in the coil? I have ordered a new set of coils but if I could add oil I could keep them for spares.

Re: Coils leaking oil
RUSS TILLEY #822868 09/08/20 8:23 pm
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Look up transformer oil.

Re: Coils leaking oil
RUSS TILLEY #822891 09/08/20 10:08 pm
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I don’t know how you would know if the oil loss was “small or large” without comparing the present weight to the original weight of the coil. Any oil loss has likely been invisible to you, and has probably leaked to a place where you can’t positively identify it anyway.

I never new that Lucas coils were refillable, I’m pleasantly be-staggered!

I think it is the primary windings that we’re primarily concerned with.
If the coil with a slightly low oil level is mounted horizontally, all the exposed “out of oil” segments of windings will still be in close thermal contact to windings that are still in oil, and so reasonably cooled.

However, if the coil is mounted vertically, an entire series of windings at the upper end will be exposed (lacking oil) and have no cooling. This may be the worst scenario, and perhaps most prone to early failure.

Just thoughts…


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