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MG TD TF 1500 - Spark Plug Gap?

Hello All,

I just installed the pertronix electronic ignition in the TF. What spark plug gap should I be using? I seem to remember seeing 0.035" somewhere.

Thanks and Cheers,
TF 6846 XPEG 797
Greg Van Hook

Greg - The gap would only be opened further if you nstalled a higher voltage coil also. The Pertronix ignition module alone doesn't need a wider gap. Cheers - Dave
David DuBois

I am using a modern Lucas Sports Coil with my Pertronix. Should I open my plug gaps to 0.035?

L Karpman

I've got the Pertronix and resistor plugs, Sport Coil that was standard on the TF's and I run .035". Seems to be a good combination. I kind of like the wider gap as long as I don't get missfires.
R. K. (Bob) Jeffers

Hi Dave, Thanks. Just so I understand -

Pertronics + "normal" coil = standard gap (0.020" - 0.022") or maybe 0.025" as recommended in the NEMGTR restoration manual, or

Pertronic + Sports Coil = 0.035" gap.

Do I have that right?

Greg Van Hook

Bob, I think I posted a thread about this a long time ago... My TF has a gold-colored coil, but it is not labeled "Lucas Sports Coil". I don't think we ever ever figured out if it's a sports coil or not.

Is there a way to test it to see if it's hotter than normal, like with an ohm meter or something?

Anyway, while I'm at it, I'm going to try to upload a picture of my TF.


Greg Van Hook

Greg -- You can determine the turns ratio if you can find someone that can measure inductance. The turns ratio is the square root of the quantity secondary inductance divided by the primary inductance.
Orig TD type Pri. Res=4.39 Sec Res.=5.19K
LA-12 Pri Res=3.3 Sec Res=8.25K
SA-12 Pri Res=2.6 Sec Res=10.05K
SP-12 Pri Res=3.2 Sec Res=8.66K

The original TD type was labelled Q-12, these labels were on the bottom of the coil. The only one specifically labeled Sport Coil was the SP-12. (As far as I can determine).

The turns ratio is what determines the output voltage. These were Q-12 48.7, LA-12 was 70.9, SA-12 was 85.7, and SP-12 was 89.1. I know this doesn't sound like high enough ratios to produce the kind of voltage that the advertising talks about but what you probably don't realize is that there is close to 400 volts on the primary when the secondary is loaded with the distributor and a spark plug, about 600 volts when not loaded.

The LA-12 is the aluminum colored body type found originally on the TF's.

I hope the above data comes out readable on the BBS.
R. K. (Bob) Jeffers

Hi Bob - thanks for useful info. on output of Lucas coils. As far as I know the original coil for the TF was also a Q12. Since all Lucas equipment has a date on it, I was able to check that the coil on my 1954 TF was a Q12 from March 1954 and this only expired last year! These coils are narrower than later coils and from original period photos relating to both 'T's and Morris Minors were painted black. The after- market 'sports' coil then was I believe an HS12. I know in the 1960s - 70s people went around saying they had a 'sports' coil on their car in the mistaken belief that somehow they would go faster ! There was also a large element of one-upmanship and I dread to think how many perfectly sound 'standard' coils ended up in a waste bin! Presumably the factory chose the 'standard' coil 'cause it was the correct specification and also a bit cheaper than the unnecessary 'sports' coil !

I try and use older second hand Lucas coils from the 60s and 70s that were made in the UK to a high standard. I paint them black and they look 'original'.
Current Lucas labled car equipment is now sourced from around the world, is of dubious quality and certainly not worth paying a premium price for! At a recent car meet I overheard someone going on about their 'sports' coil so nothing changes!

My experience is that a well made coil can last for 50yrs so if the one you are using now is OK stick with it and don't worry whether or not it says 'sports' on it. All 'modern' coils will have an output voltage well in excess of the needs of our 50 year old cars!

Anyone else got info. on Lucas coil specifications ?

Cheers John.
J.C Mitchell

Hi all - further Lucas coil info:-

DLB 101 Standard Coil
DLB 102 Standard Ballast Coil(not for 'T's)
DLB 105 High Performance Coil
DLB 110 High Performance Ballast Coil(not for 'T's)

A copy of the original Q12 coil is offered by Holden Vintage & Classic Ltd in the UK at 01885 488488 at around 41-00 for anyone who is interested.

To correct my previous thread re. current Lucas equipment I meant to refer to coils only and since Lucas stick on labels are now available the source and quality of 'Lucas type', labeled coils is often in doubt.

Cheers John.
J.C Mitchell

This thread was discussed between 20/06/2007 and 27/06/2007

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.