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MG TD TF 1500 - Installing New Coil on 52 TD

I just bought a new coil for my 52 TD. I tried to save a few bucks so the new one is not exactly like the old one that has a metal clamp built into it with attach holes into the firewall, it's just a cylinder with no clamp. Is there a good method for attaching the new coil on the sloping angle of the firewall?

Also the original is marked with an upside down CB at the inside electrical attachment by the battery and the outside away from the battery reads MS. The new one just has - and + and doesn't have the mount piece to provide orientation, so I can't figure out whether the positive or negative should be on the battery side? Thank you.
F W Abel

These coil mounting brackets were often separate from the coil and were used on many British cars From Morris Minors to Jaguars. Someone on the forum will probably have a extra one. The new coil probably assumes your car is negative ground as are all modern cars and British cars after alternators were fitted. Many positive ground cars have been converted to negative ground. What is yours? CB usually stands for Contact Breaker and MS perhaps Master Switch? Some are labeled CB and SW.
John Quilter (TD8986)

Thank you, John. MS upside down is SW so I think the original coil I'm removing is CB & SW. Is one positive and one negative?

My car is positive ground. The new coil with the + and - markings is a UC-15 which the sites show is for MG TD but I can't find any information on it's polarity. This is somewhat complicated by the fact that the batteries I now get have - on the ground. I think they make a more modern version of the same battery that looks identical but the markings of the terminals are reversed, the left terminal is + on mine but the right terminal is + on the other one. I've had the car since 1971 and I don't think the polarity was ever changed.
fwa Fred Abel

So on the new coil it has + and - instead of CB & SW. Can you tell from this diagram which would be + and which would be - ?

F W Abel

According to this diagram I would think the CB is the - and the SW is the + ?

F W Abel

FW - Since your coil is positive ground, the + terminal on the new coil goes to the distributor (CB on the old coil is the same as +) and the - goes to the ignition switch or anywhere on the white, switched circuit. Cheers - Dave
PS - even if you get the coil installed backward, you will probably not be able to detect any difference in the running of the car - having the coil in backward, will only decrease the high voltage going to the plugs by 12 volts.
D W DuBois

Here's what you need. Inexpensive and can be had from ebay or other sites on the net. PJ

Paul S Jennings

Moss has the mounting bracket from $4 to $12.50 depending on chrome or zinc plating. I bet you can get one at any auto parts store. Jud
J K Chapin

If you want to be "concours" ... the original coil bracket did not have the mount for a condenser cut into it. The Moss bracket and most coil brackets from your friendly local auto parts store have the condenser mount.

Lonnie
TF7211

Original coil and bracket on unrestored TF9052 ...

LM Cook

I agree Lonnie, the bracket should be plain. Painted my coil before I realized they weren't painted. Not going for 100% concours so it's staying painted for a while. Easy to redo if needed.

Paul S Jennings

I seem to remember being told (many years ago) that if the coil is installed backwards that the spark will jump from the "plug to tip" instead of "tip to plug" this would be where the 12v hi voltage loss Dave D stated comes from.
I can only think of one time I needed that info and that was with a 56 Dodge Royal I bought many years ago for $25.00. It had no coil when purchased ...among other things missing. (most of the floor for one)
After observing a plug "firing backwards" on the end of a plug wire I swapped the coil wires and that car ran much better...and for quite some time.
David Sheward 55 TF1500 # 7427

I'm totally out of my element here so I'll go ahead and pontificate without any basis. I can't imagine that the fuel/air mixture much cares which way the spark jumped since its a goner either way. I suspect, however, that the plug may care - the philosophy of positive earth was a belief that the plugs (and maybe the points but I doubt it) would last longer if the little electrons were jumping from center electrode to the bent electrode. I think that belief has been debunked but you couldn't prove it by me. Anyway, I can't see how reversing the wires on the coil would change the direction of the spark. If the car is positive earth the electrons are going to jump from the center electrode (-) to something touching the block (+). At least I think so. Jud
J K Chapin

Thank you very much for all your great input. I did buy a universal bracket at a local parts store tonight to get the car running again, I'm putting it back together tomorrow.
F W Abel

http://mgaguru.com/mgtech/ignition/ig104.htm

I think this is basically correct. You want the plug tip to be negative because it's hotter, so you get better electron emission.

In fact, the voltage at the plug is AC, not DC, so all this applies only to the initial half cycle at the plug. But I guess it still matters somewhat.
S Maas

"The engine still runs either way, but spark might be more reliable under marginal conditions if you get it right."
"Marginal" would pretty much describe the entire vehicle in the case of my old 56 Dodge and maybe why it made a difference on that one!
I was 16 and "learning" the plug gap was no doubt set to what ever it was last time the plug was dropped on the pavement. LOL
David Sheward 55 TF1500 # 7427

I put the coil on my TD and hooked up the connections. When I went to screw the distributor cable into the coil I got a big surprise when the fitting on the coil was not a screw type connection. Is there a connector I can get that will enable use of my distributor cable with the new coil? Thanks.
F W Abel

Hi Fred,

There are various type of coil which differ in their terminals - both the high and low tension sides. An original T Series coil has an "acorn" HT lead fitting which is basically a threaded bakelite bush which you push the lead through, splay the ends of the wire and then screw into the coil. These are now quite expensive to buy and many people replace them with the modern "push fit" HT connection. These coils don't have a screw thread for the HT lead. You fit a simple brass ferrule round the end of the lead and then push it into the coil. The ferrule holds it in place. Looks like you have purchased one of the latter types and you may need the ferrule. Regarding the low tension wires, originally these were fitted to brass screw posts on the coil. The next stage in the development was to use spade connectors and the male part of these were fitted to the coil using the screw posts. You can easilly convert these to the "correct" type removing the nuts from the posts and throwing the spade connectors away. Finally the scres/nuts were replaced with rivets and you are thus stuck with spade connectors. Also if you are buying a new coil make certain it isn't one with a "ballast resistor". These are rated at 9V rather than 12V. When in normal use the ballast resistor cuts the battery voltage from 12 to 9. When the starter key is turned however, the resistor is shorted out and 12V is supplied to the 9V coil. This is to aid starting when the draw from the starter motor can reduce the voltage available. If you run one of these continuously without a resistor it will burn out.

The contact breaker in the distributor makes/breaks a connection to earth. In cars up to the 1960s this was almost allways positive. The coils were labelled CB (contact breaker) and SW (ignition switch). Thus the CB should be connected to positive, or in the case of an original car, the contact breaker. If you swop to negative earth the CB terminal must then be connected to the, now positive, ignition switch. Coils with a + and - near the LT wires are from more modern, negative earth cars. If your car is positive earth the + goes to the contact breaker, if the car has been converted to negative earth it is the -

Must appologise for the rambling post - it is snowing in Scotland, the garage is too cold to work in and I have nothing else to occupy me.


Jan T
J Targosz

Hi FW,

For detaied info. on coils look at Archives under 'original ignition coils'. To summarise the finish, all the T series Lucas coils until late 1954 were Q12 type non oil filled, the mounting being integral to the body, which was narrower than the later types, and painted black.

The later siver coloured LA12 coils came in around November 1954, and therefore strictly speaking, are only correct for late TFs. However most of the solid Q12s are long gone, although mine lasted 50years, and I now use s/h 1970s-80s ones picked up at autojumbles etc, and sprayed black. These were made in the UK and very reliable.

Don't forget the Birmingham Lucas factory was pulled down in the 1980s, and they ceased making auto equipment from that date. All the so called 'Lucas' equipment you see in green boxes is merely a franchise item that could be made anywhere, and in my experience is of very variable quality! BEWARE.

Cheers,

John
J C Mitchell

Well heck, John. I was proud of myself for installing a silver colored no-name coil, fake Lucas label, and bracket on my TF-1500 to make it look like the coil on unrestored TF9052 which was built 25-Jan-1955. My chassis number is TF7211, built 23-Sep-1954, so I didn't do as well as I thought.

Thanks for posting. I love these little details.

Lonnie
TF7211
LM Cook

"I'm totally out of my element here so I'll go ahead and pontificate without any basis."

Well, Ive re-read Rick Astley's book and he confirms that I didn't know what I was talking about. Switching the low voltage leads on the coil does reverse the direction of the spark. The attached diagram is from his excellent work. Jud

J K Chapin

Hi Lonnie,

Sorry - I didn't mean to upset anyone! It's good that your original Lucas LA12 coil is still functioning on your 55 TF - the original UK Lucas factory stuff was generally of good quality. My TF 1500,chassis no. 7973 was built in November 1954 and still had the original Q12 solid type coil until a few years ago.

To keep an 'original' look I spray a later Lucas coil black, including the bracket. Up until the 1970s-80s the lucar spade low tension connections can be removed, and the bolts used. If lucar spade is not removable open up the hole to take a small nut and bolt. As far as the HT lead is concerned, a tap can be used to cut a thread ( Whitworth/ANC I think )inside the newer coil, and the original HT screwed nut fitting used. Being plastic the tapping match is not critical, or you could just push the ignition lead into the coil, and cover/secure with a commonly available plain rubber 'bellows', often used in the past for waterproofing on cars/motorcycles. Or file/ turn down the threaded part of an original ignition nut to a push fit - padded with tape if you overdo it - can't be seen!

Hope this helps,

Cheers,

John
J C Mitchell

Nope, John ... I don't have the original Lucas coil in my TF.

I have a non-branded natural metal coil with screw in high tension terminal from British Parts Northwest.
http://www.bpnorthwest.com/ignition-coil-w-screw-in-ht-lead.html

And fake shiney HA-12 sticker Moss #215-630.

I did some searching and found a thread about the two TF coils in the archives that included posts by you and by me. I guess I assumed that my car had the newer coil since it is titled as a 1955, although it was built in Sept 1954.
http://www2.mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=8&subjectar=8&thread=2010112222112928385

Lonnie
TF7211
LM Cook

Hi Lonnie,

My mistake - I thought you also had TF9052 as well as TF7211. Now you know it should probably be black etc, are you going to take the label off and convert? Ignition and low tension connections can be made 'original', and I would use satin black by choice - I use an aerosol on top of a primer, lightly sand original for grip.

Cheers,

John
J C Mitchell

This thread was discussed between 07/12/2014 and 11/12/2014

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