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MG MGB Technical - Coil orientation

There's a semi-heated debate in progress on another MG site, regarding coils, i.e., up, down, sideways.
Those who think down, for terminal insulation reasons. Those who are "uppers" for possible leak prevention and maximum oil coverage of the iron core, for cooling reasons. Then there's the on their side brigade, terminals horizontal, presumably best of both worlds.
What is totally absent from this debate is an input from Lucas, Bosch etc., who actually manufacture the things.
Has anyone had such a definitive input, or are we all working on habit and "old wives tales", as some would have it?
I'm trying at present to obtain an answer, no success as yet.
Allan Reeling

Allan. As you see all the 3 positions you mentioned used by on standard production vehicles by different manufactures, (not a definitive answer) but I would say it makes no difference, however I have seen problems with ones pointing down, when the clamping screw has come lose and the coil has slid down and shorted the SW wire out and burnt the harness
Andy Tilney

Definitive? After all this time I doubt you would get that from Lucas, who today only own the rights to the name, I doubt any original engineers are still there. Maybe Bosch.

It probably depends on the vehicle designer. Originally MGB coils were mounted horizontally on a bracket mounted on the engine. Perhaps not ideal as it would pick up heat from the engine.

Quite soon they seem to have moved to the inner wing pointing downwards, and I believe this is the way that 'wet' or oil-filled coils should be mounted.

The Lucas Fault Diagnosis Service Manual shows them all drawn pointing upwards, but how much credence can be placed on that I don't know.

The Leyland Workshop Manual describes a test-rig and includes the following:

"The coil must be mounted at an angle of 45 degrees on the test rig with the CB terminal uppermost and the coil case earthed.

"The mounting angle ensures that the primary winding take-off to the LT terminal is not covered with fluid and any internal tracking between the iron core and the primary lead will be shown up during the test.

"Earthing the case detects whether or not short-circuits to earth are present."

Note the 'not covered'. I believe that refers to the oil in the case acting to prevent internal arcing and hence tracking and breakdown when in service, and for that reason wet coils should be mounted nose down to ensure the internal connections are covered in oil.

At the end of the day, mount it how it was originally. How often did they fail mounted that way from the factory?
paulh4

My 1980 Roadster , purchased from new, came with the coil (silver finish on the outside) pointing down. Last year as part of a renovation / determination to cure a miss fire i replaced the original coil with one from auto sparks (black finish on the outside). After resolving the miss fire problem elsewhere & refurbishing under the bonnet i recently decided to put the original coil back in but added a stainless steel sleeve & clamp to smarten up the appearance of the old coil.
Once bolted back on the side of the inner wing
i realised that the coil would slide quite easily within the sleeve when connecting up the wiring again (even though i thought i had tightened up the clamping screw sufficiently before fixing the coil back in the car). Needless to say i took the whole thing out again & tightened up the clamping screw until i was absolutely sure the coil wouldn't move.
Andy is therefore absolutely right to point out the dangers of a loose clamping screw with the coil facing down which is evidently even more relevant where the smooth finish of stainless steel is added into the equation!
Charles9

Generally speaking I'm with you Paul.
The "leaking" brigade I think are missing the point, namely if it's leaking, it's faulty therefore replace it!!!
Whether the vehicle manufacturers gave any regard to orientation, (as opposed to positional expediency), I doubt. Bracketed to the engine or the dynamo seems very lacking in sympathy for oil filled coils as regards heat and vibration.
Whether coils are absolutely full is another issue. Some "slosh" when shaken, most don't. Any air in there is likely to test the end seal when the coil heats up, so you would think is better excluded, but the oil will expand anyway.
Allan Reeling

Well, if there is some air in there it will absorb the expansion of the oil without testing the seal too much, rather like a combi-boiler expansion vessel. If full of oil and no air it is more likely to leak then when heated.

I don't know how much space there is inside a coil for sloshing. Many many years ago I cut open a coil to see if I could find out where the sparks came from, but found only miles and miles of wire, funnily enough. However when ballasted systems were developed using a 6v coil, there is only half the length of wire in the primary winding. And it's a short but clever leap sideways from there to using a 6v coil as the basis for 12v coils as well, as all the latter needs is much smaller amount of resistance wire to bring the total resistance up to the 3 ohms of a 12v coil. That would leave more room for slosh. The relative weights of old-style 12v, modern 12v, and 6v would be interesting.
paulh4

Our TD (since 1974) came with the coil mounted in the usual position (left side on the firewall with the coil mounted, pointed down). Except for the four years that I restored the TD, it has been nearly a daily driver (the only time it is not driven, is when there is snow on the roads). As far as I know, the coil is the one that the car came with the factory and so far, it has not leaked or given us any problem what so ever. This is not to say that the coil will never leak, but as such time as it does, it will remain in it's original position. Can't say the same about the coil in our MGB. Cheers - Dave
DW DuBois

I must admit to having run coils in all sorts of poitions, but the correct way they taught in trade school was, Oil filled top up, solid fill anyway. Some oil filled coils were critical and unsafe if fitted incorrectly. In the 80s at least some Bosch oil filled coils were capable of 60,000 volts and had to be fitted top up, with a small pressure relief port towards the engine to prevent scalding (Mechanic). They had instructions on the out side. They were and are still common here in AUS. Denis
D M Hill

This thread was discussed on 27/08/2018

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