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MG MGA - Screw-in Coil

I'm sure this is simple if you have done it once before but I can't seem to make sense of it.

I am replacing a push-in style coil with a screw-in style from Moss. No instructions included.

It comes with a plastic "thing" with threads on the inside that holds the wire. There is an aluminum type of clip and a washer. How hard can it be?

Maybe I have to stop drinking Newcastles while working on the car.
Jeff Bennett

Not quite sure what the aluminum clip you are talking about looks like. I always just strip about an inch of insulation off the end of the wire, put the wire through the plastic cap, then wrap the exposed wire around the washer a few times. Perhaps the aluminum clip is for resistor type wires which don't really have a wire core. With resistor wires, you generally have a clip that has a prong or two that you press into the carbon coated cloth center of the wire.

Jeff Schultz

Okay - that makes sense. I think your right about the clip. It does have two prongs.

Thanks
Jeff Bennett

Jeff. The original wires were stranded, copper wires. You stripped a quarter inch of insulation off the end of the wire, pushed the strands through the hole in the aluminum piece and spread the wires out, in a circle, to make contact with the terminal inside the center post of the coil. The plastic nut was tightened down to hold the aluminum contact firmly in place.

Les
Les Bengtson

For what it's worth; I think they sent you the coil for a T-type. The coil on my TF is a screw-in one.
David Werblow

David. The MGAs, MGBs and Sprite/midgets used a screw in connection coil up until the mid to late 1960's. They also used wire spark plug leads rather than the carbon fiber or silicone leads which became the standard later. The change in spark plug leads came about due to the "upgraded" sound systems being offered for the various new cars. The old style wires put out some RF interference, one of the reasons a capacitor was sometimes attached to one terminal of the coil in an attempt to mitigate the RF interference of the ignition system.

I am not sure when the change over took place on British cars. I remember it first on a 1972 Ford that my father had. But, all of the MGAs came with a screw type coil. However, unless one wishes to build custom spark plug wire sets (the better auto parts stores may still carry the bulk wire and connectors) the more modern style coil works just fine for non-show cars.

Les
Les Bengtson

Moss offers two coils. The standard coil with screw in connection or the sport coil with push in. About $15 difference.
Jeff Bennett

Jeff. Any 12V coil, as long as it is not marked for use with an external resistor (i.e. one designed to operate on a full 12V as most of the older US and foreign cars were) will work in an MGA. Nothing special about the Lucas coils except if you are running a show car. Either style coil can be set up to work with either the original side entry distributor cap. If using the later Lucas 25D4 distributor, you can set the system up to use the top entry cap should you so desire. Good thing about the top entry cap is that you can always fine a wire set to fit it. Good thing about the side entry system is it was designed to work with copper core wires which seldom need to be replaced. A personal choice thing that does not matter with a driving car.

Les
Les Bengtson

Jeff, Keep an eye on your coil, I bought one new from moss and little did I know that the oil was slowly leaking out of it. As soon as it got hot the car would not start. Drove me nuts for 4 weeks. As more oil leaked from it the faster it would get hot. Kept getting stranded everywhere I went. Finally it blew! See pic below! I replaced it and problem was solved. Starts on a dime every time :)


WMR Bill

To further Les's comments, I have run coils bought at the local farm store. They are generic 12V coils with push-type HV terminals. They list Allis Chalmers and other tractors on the package as suitable aplications. Less than $20 bucks and available with no waiting. I was comfortable in this since a club member broke down once in the middle of farm country. He went to the local tractor repair shop and the found a spare, used coil rolling around in a desk drawer. I think he is still running that same coil today some 17 years later.

I also run Bosch "wires" that are graphite core in the original side entry cap and the original style suppressor caps. The screws poke into the conductor and have never given me any sign of trouble. Now the rotor, that is another story.

Chuck
C Schaefer

Here is a picture from an auto books manual. It shows what Les spoke of.


R J Brown

I guess they don't make things like they used to,I'm still on my original Lucas coil.
gary starr

Bill - yep, that's the same coil I purchased from Moss.

RJ - Thanks, a pic is worth a 1000 words. That is how I set it up although I don't believe my wires are copper.

Saturday this old girl is going to start!!!!
Jeff Bennett

Speaking of coils, two questions come to mind: a) what should a coil's temperature be when operating normally; and b) I've heard that adding a ballast to a normal 12v coil enhances the quality of spark by reducing the ignition system feed to 9v but leaving a full 12v for the starter motor - does anyone have the latter set-up and if so is it worth the while?
Joe Gates

Joe,
My coil runs too hot to hold my hand on as does the generator it is mounted to. This is normal. I have found that, for me, about 150deg F is about my limit. This is no problem for a coil.

As far as your second post, what you are describing sounds like a normal balasted coil system. Its coil is designed for a lower voltage operation so there is no difference in performance from a 12 volt coil. It normally runs at the lower, balasted voltage level. The system is designed to bypass the ballast during the starting. When the voltage drops from the high current draw of the starter, the coil gets more power than if it used a non-balasted coil. I have never heard of using a 12V coil and a ballast resistor.

Chuck
C Schaefer

Joe Chuck is right. The two systems should not be combined. A 12v coil designed to be used without a resistor will perform poorly with a resistor. A ballasted coil is used to improve the spark while the starter is engaged. Adding a resistor to a 12v, unballasted, coil will do just the opposite. Degrading coil opperation all the time and even worse while cranking.
R J Brown

Thanks guys. What you say makes sense. I am a techno-peasant, so forgive the follow-on queries about interpreting the consequences of a balasted coil system.

Do I understand that upon starting the engine, both starter motor and coil momentarily receive 12v with the spark plugs benefitting from 33% more effective charge (12v through a 9v coil = 16v) or do the spark plugs still receive 12v delivered by a 9v coil by only using 75% of required power off the battery (9v drawn to deliver 12v)?

Secondly, if thereafter the coil only requires 9v, is an ancilliary benefit that the battery operates in a less stressful environment - continuous recharge to 12v via alternator or generator versus a continuous draw of only 9v (assuming no other power requirements e.g. lights, radio, etc)?
Joe Gates

Joe. I believe that the ballasted coils are designed for a normal 6V operation(not 9v). The ballast resistor is enought to drop the other 6V. 6V coil + 6Volt resistor = 12V system. During the starting, the system voltage (12V) drops to something less lets say, 9-10V due to the high current draw. During this time the ballast is bypassed and the 9-10V is applied to the 6V coil. Once the engine is started, the ballast resister is un-bypassed (is that a real word?) and the system goes into the "normal" running mode.

There is no "less stressful" environment. And the ballast system is slightly mor complicated that te non-ballasted system. The Ballast resistor provides no ancilliary benefit. It is just designed to give a more powerful spark during the starting period. Modern computer controlled systems can be much more complicated than these two basic systems.

I run a standard non-ballasted system and would not recommend changing anything. Incidentally, if you hand-crank your car for starting, there is no voltage drop during the starting period since the starter is not energized thus eliminating the need for a ballasted system. (only joking).



Chuck
C Schaefer

This thread was discussed between 16/01/2008 and 19/01/2008

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