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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Distributor/coil

Could somebody please explain to me two things.
1. What is the difference between a ballasted non-ballasted coil. Moss lists a Crane (ballasted) and Lucas (non-ballasted).
2.Under distributors Moss says "Shaft must be drilled for drive dog (not included). What exactly does this entail, is it something that is easy to do or does it require special tooling? Greg & Grimm
G.J. Cenzer

Ballast is used to reduce the ohmage (resistance)of coil for use on our cars.
Do you really "need" a new dizzy? Take a look under the plate for the points...I am wondering if you are having same problem I did. One of the springs for the advance on mine had broke. This resulted in the car running fine @ low RPM but it would lose power at higher RPM's. Caused no doubt by PO not lubing per manual so it rusted and broke. I cleaned mine out, installed new springs, new Lucas sports coil,(correct ohms, painted it black & stuck a "lucas" sticker on it so it looked right), and installed a pertronix pointless ingnition.
Far less Expense and hassle than replacing with a big red MTD unit...and it is hard to tell from orginial. Haven't had any problems for a few thousand miles now and starting was much improved with the Pertronix installed.
Cheers,
David 55 TF1500 #7427
David Sheward

oops..
#2 never had to drill my drive dog (they are both males...and get lose offten enough to do their own "drilling"...don't think they would care much for that!) so can't answer that one for you!
David Sheward

David,
Where did you buy your Petronix Ignition and Lucas coil. The Petronix eliminates the points?, where does it mount, inside the distributor? Wouldn't the mechanical advance be required for a points ignition whereas the pointless would affect the advance electronically? just trying to get educated on this new stuff.
My distributor had only 1 clamp on it but it still ran. I fabricated a clamp out of an old MGB clamp I had. It was too long so I cut the top off, whitney punched a hole and added a screw which engages the top so it now stays on nice and tight. My upper clamp touches the breather pipe and is almost impossible to un-snap without removing the tappet cover.
Greg & Grimm
G.J. Cenzer

The idea behind the ballast resistor on a coil is to improve cold starting, it works in the following way, The coil is rated at something less than 12volts e.g. 6volts. The ballast resistor, in series with the coil, has then 6 volts across it during normal running, however during starting (when the solenoid in closed) the ballast resistor is shorted, putting a full 12 volts across the coil, the result is a good spark when cranking the starter motor. As our TDs do not have solenoids we cannot use this feature. A secondary advantage this configuration, that as some of the heat is dissipated by the ballast, the coil runs cooler.
About your drive gear question, the drive gear is fixed to the distributor shaft by a pin the new shaft does not have a hole drilled in it, for this pin, you need to drill it yourself.
John Scragg

G.J.

The Mallory dual point dizzy comes with a plain shaft with no drive gear or "dog" fitted. You must remove the old one from your original dizzy, which is not hard to do with a hammer and small punch to push the pin securing it out. Slide the dog (on MGA & B's)or gear(T's) onto the Mallory's shaft with the new thrust washers supplied and then mark and drill the shaft for the new (roll)pin supplied. Drive in the new pin with your hammer and punch and your in business. A very easy job to do. The Mallory is a great unit and works well. With it's dual points you get a longer period of "dwell" and a hotter spark because of it. The points will last damm near forever and you can also purchase spare points, condensor, cap & rotor at any NAPA store. I have fitted several Mallory dizzys to various engines over the years with positive results, I recomend them highly.

Ciao, Ben T.
Ben Travato

Greg, take a look at
http://home.earthlink.net/~budkrueger/Pertronix_Into_TD.html
for installation. I'd suggest Skip Kelsey of Shadetree Motors (http://www.shadetreemotors.com) as the best source for the purchase. IMHO.
Bud Krueger

Bud,
How do I determine if I have a distributor with symetric/asymetric cam. On Shadetreemotors site Skip says one is for symetric or high lift cams only and the other is for asymetric cam only. Sounds like the way to go just want to make sure I get the right one for my car. Greg & Grimm
G.J. Cenzer

Greg, best way is to give Skip a call 925-846-1309. You can also look in the NEMGTR T Type Restoration Handbook. Actually, if you guess wrong, the only difference is in the magnetic sleeve that fits over the cam. You may have to dig out your pocket knife and whittle out a little bit of plastic. Talk to Skip.
Bud Krueger

Greg,
Bud has you pointed in right direction for Pertronix> Do take notice that they are made for poss. and neg ground systems also and are not interchangeable...so that does need to be taken into account.
Cheers,
David 55 TF1500 #7427
David Sheward

The difference between a symetric or asymetric cam is not discernable at least to this old guy from pictures in the manual or in Chip Olds SCO article. If you want to know what cam you have you need to phone Moss and get the specs across the flats of the cam and then measure with a micrometer and order the right one + or -. The asymetyric is larger and I can tell you that you can ruin the symetric magnetic sleave by cutting away at its inside diameter. Terry
Terry O'Brien

With a great deal of helpful advice from Bud Krueger I just installed a Pertronix igniter and Lucas Sport Coil in my 51 TD.

There seems to be a general confusion about cam identification. The following tidbit of information may be helpful: (based on Bud's High-Lift cam and my Symmetric cam - a very small database)
flat-to-flat corner-to-corner
High-Lift 16.20 mm 19.00 mm
Symmetric 16.84 mm 18.95 mm
Asymmetric ? ?

I think, based on the diagram in the shop manual, that the Asymmetric may be longer on one diagonal than the other. Can anyone provide measurements?

Anyway, Pertronix supplies one cap for both Symmetric and High-Lift cams. I can attest that the cap does not fit Symmetric. Bus told me it fit his cam without a problem.

I made the cap fit by gently tapping the cam into the cap, then carefully cutting off the resulting plastic ridge. Then repeating until the cam finally fitted.

Hope this helps.
Ted Jackson

Pertronix now recomends a 3ohm (minimum) coil for their 4 cyl. units!!!(after i had 2 units start to misfire, see p.s. below} Also the bottom of the rotor may need to be slightly ground down, or the magnetic sleeve stop removed for the rotor to sit all the way home.(watch for the distributor cap jumping around at idle!)They have a great warranty policy/great customer service.But with these issues, Ben T. has an alternitive, his advice is always welcome, & always accurate.P.S.(My Q12 coil reads 4.3 ohms, lucas sport coil, which was installed inconjunction with the pertronix, reads 2.4 ohms}Len
Len Fanelli

Len, what is a Q12 coil and who sells them.
Based on the 3 pics in the shop manual my dist. is deffinately an Asymetric. Since I had to take off the dist cap to inspect the cam I installed a new set of points/condenser. I am getting a dwell reading of 36 on my dwell meter, what is the prefered dwell number for the TD? This is only temp to keep Her running as I want to add Pertronix and new coil. Greg & Grimm
G.J. Cenzer

The Q12 is the original coil, no longer avalible. Moss sells a copy of it.
Len Fanelli

I fitted an Aldon Ignitor electronic points system to my Lotus Elan. The distributer is under the carbs and is just about unreachable. The ignitor fits in the distributer itself and looks 100% original. It has been faultless in the Lotus. I note Holden Vintage and Classic sell a similar unit called the magnetronic at £80. You can see a picture of one - and lots of other period electrical stuff - at www.holden.co.uk


Jan T
J Targosz

Jan: What you have sounds very much the same as the Pertronix, except for the price. The Pertronix is about half the price. I read somewhere that the asymetric cam only just exsisted ie very rare. We phoned Moss from the shop for the specs so I am going from memory but they said that across the flats the asymetric was 0.705 while the symetric was something like 0.650. I assume these are imperial measurements. Anyway removing .055 ruined the magnetic sleeve and it is not the way to go. Pertronics warranty is very good and they are sending me an asymetric sleeve. By the way they sort of confirmed that the asymetric is rare as the only make them to order. Terry
Terry O'Brien

I, too, had a very difficult time trying to identify the various cams used in the distributors of our cars. In looking at the illustrations in the Workshop Manual, I finally noticed that the slot for the rotor is in a different location for each shape. I colored the illustrated slots with a red pencil and then was very easily able to recognize each type.
Jim Merz

The ballast resister is used to reduce the voltage at the points by 50%, which results in longer point life. Some MG's have a resistance wire between the coil and the distributor. If you replace it with ordinary 14 ga. wire point life will suffer.
Many 6 volt cars have an added switch which provides a full 6 volts for starting. This is switched off once the engine is running so that only three volts is sent to the points. Some cars use a Ford type, 4 post solonoid which does the same thing automatically. They are available in 6 and 12 volt versions.
S.R. Barrow

This thread was discussed between 20/08/2004 and 13/09/2004

MG TD TF 1500 index

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