Coil Mounting Query

U

ursus

Well-known member
Currently replacing a faulty older coil with a new unit. Unlike the old coil, the new unit is liquid (oil?) filled as evidenced by the sloshing sound when moved back and forth.

I have been informed by many sources that a liquid filled coil must be mounted so that the contacts are facing upward in order to prevent overheating and early failure. However, I have yet to see a coil mounted on a Model A firewall in this manner and am curious how this can be accomplished given the length of wires associated with the stock orientation. How do others mount the coil facing upward or is the caution noted regarding liquid filled coils something to disregard?
 
Yes, new, oil/liquid filled coils need to be mounted upside down, meaning the connections point up.

They will leak, that is the reason, it's not because of overheating or failure. They leak, then fail. Unfortunately they are not the old epoxy filled coils that lasted a long time.
 
Hitman said:
Yes, new, oil/liquid filled coils need to be mounted upside down, meaning the connections point up.

They will leak, that is the reason, it's not because of overheating or failure. They leak, then fail. Unfortunately they are not the old epoxy filled coils that lasted a long time.
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OK, but how then is such a coil to be mounted on a Model A firewall? The stock type coil and ignition wires would be too short to reach the top of the coil. I have been looking all over the Internet for photo examples of "A" firewalls having this mounting arrangement and coming up empty.
 
There are coils that don't have liquid insulation inside. There should be some available that have epoxy insulation. The OEM coils had bitumin or tar, for a better word, inside as the insulator. Just make sure it's a 1.5 ohm coil.
 
Going through my records, in April 2015 I bought a longer-than-usual coil wire from Mac's; it was advertised as 17 1/2" long, specifically made so that it would reach from the coil to the distributor when the coil is mounted with the contacts at the top - which is how I use it (my concern at the time was that a liquid-filled coil could develop a leak if mounted with the contacts facing downward).

Looking at my invoice, it was called "Model A Ford Coil To Distributor Wire -Modern - 17-1/2 Long", and the part# was 28-21387-1.

Looking at Mac's (now Eckler's) current website, they still are selling a coil wire with that part #, but do not describe what length it is on the webpage (although if you look at the URL, it says "https://www.ecklers.com/model-a-ford-coil-to-distributor-wire-modern-17-1-2-long-28-21387-1.html"), but that doesn't mean that the one they currently sell is actually 17 1/2" long, they may have just never updated their website URL for that part.

I also notice that the price is now nearly $20 (vs. the $3.95 I paid back in 2015).

I suppose you could ask Eckler's how long it is before committing to purchase it - it'd be free to try.
 
You can mount oil-filled coils head-down. They are more likely to leak this way, but they don't always leak, particularly if the car doesn't see heavy use. You certainly can mount it head-down temporarily – spending a few months in that position won't hurt it.

The long term solution, as others have said, is to get non-authentic wires that are longer, or solder extensions onto the wires you have.
 
ursus said:
OK, but how then is such a coil to be mounted on a Model A firewall? The stock type coil and ignition wires would be too short to reach the top of the coil. I have been looking all over the Internet for photo examples of "A" firewalls having this mounting arrangement and coming up empty.
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You just modify your existing wires by soldering extensions to have them fit, and make a new coil wire if necessary. It also helps to slide the coil down in the bracket to get it closer. You might just luck out with that, depending on your wire length.
 
I mounted my coil upright after having one leak, and another vibrate out of the bracket, short out on the motor while whistling down the freeway in a vw bug. Cooked the wiring all the way to the dash. What a mess. There is no fuse in that circuit, at least on my '71.
 

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Epoxy coils can be mounted in the original position, but have no other advantages. Oil filled coils last longer (mounted properly) and cost less.
 
Th coils Henry used were OK with being mounted terminals down. The fact that the could use shorter wires is probably why he did it. I have turned the coils in all of my cars over and extended the wires. From a failed coil every few thousand miles, I have had no problem since (about 70,000 mlies)
 
alexiskai said:
Epoxy coils can be mounted in the original position, but have no other advantages. Oil filled coils last longer (mounted properly) and cost less.
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I disagree with the point that epoxy filled coils offer no other advantages. Epoxy filled have been around a long time and are well known to tolerate high vibration and temperature environments.

The current oil filled failures seem to be associated with current coil production methods. Cheap, you get what you pay for.

I’d use a Bosch German blue coil over anything else. Never had one fail. Good thing Im an old VW guy and have a few used and NOS coils laying around.
 
Hitman said:
Epoxy filled have been around a long time and are well known to tolerate high vibration and temperature environments.

The current oil filled failures seem to be associated with current coil production methods. Cheap, you get what you pay for.
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Epoxy coils are good in high vibration and high temperature environments. Sadly, the Model A is not a high vibration or temperature environment. That's why I say it has no advantages.

Epoxy is an insulator. Heat doesn't move through it quickly. While that means it can protect the coil wiring against high ambient temperatures, it also means that heat generated inside the coil stays in the coil.

In contrast, oil is a heat conductor. It rapidly moves heat away from the wiring to the coil case, where it convects away via air currents. This extends the service life of the coil's internal insulation.

There are a bunch of guys in this hobby who appear to be dedicated to the superiority of epoxy coils, but – with the exception of "correct" positioning – epoxy's benefits only apply to situations that Model A engines aren't found in, while its drawbacks apply very much to Model A situations. The bottom line for me is that I've tested dozens of vintage Model A coils, and epoxy coils are by far the type most likely to fail testing. The data don't lie.

I agree that modern coils are manufactured to low standards, but that's not a function of whether they use oil as a medium. They're just cheap. If you want a high quality coil, you can go on eBay and buy a vintage NOS Delco-Remy oil-filled coil for $40. Get a 12V external resistor coil; without a resistor, they work exactly like 6V coils. Still cheaper than a modern epoxy coil.
 
Correct! Modern Oil filled coils will eventually leak if mounted contact side down. Price differences between them and epoxy filled (which can be mounted contact pole down) are minor.


I feel a need to disagree with "Alexiskai" regarding the Model A coil environment. It is indeed a "high vibration" environment unless modified with special engine mounts. Model A engine compartments are much higher vibration areas than modern engine compartments. For a minimal price difference in an already low cost item..why save a few cents on the coil?
 
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