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MG MGB Technical - What type of HT leads for side entry dizzy cap?

I have purchased a Champion triple silicone HT plug lead set for my 69B. I have looked in the BBS archives and found some old posts on this subject but I would appreciate some reassurance as to whether these leads will be ok to fit into my side entry distributor cap. I know this make of HT lead is on the cheaper side but I am on a budget with my resto. Also how do I fit them? Do I have to cut the top mounted push end fittings off and screw the HT leads into my side entry dizzy cap? I have also purchased a 12volt sports ignition coil to replace the worn old Lucas sports coil. Should the coil face up or down when fitted? I have seen both. Sorry for all the questions, but I know you can help!
Dave MGB

The plug leads are attached to the dissy cap with screws from the underside.
Dave O'Neill 2

Hi Dave,

Two issues I had;

1/ The diameter of the wire was larger than the hole in the dizzy cap,

2/ Somehow one of the screws, that are supposed to pierce the insulation and embed themselves in the conductor, actually somehow missed the conductor and I had an open circuit lead. Test them for continuity, albeit a fairly high resistance, before installing the cap.

Herb
Herb Adler

The side entry caps were designed for copper cored HT wires. The wires you are trying to install have carbon impregnated cotton cores and will not be a satisfactory fit. They won't give a solid enough connection, inside of the cap where the screw passes through the HT lead. If you want to stick with the side entry cap, you will have to use copper cored wires, with screw on resistors that fit onto the sparkplugs. RAY
rjm RAY

Dave says silicone, not carbon impregnated string, which certainly when I bought my V8 20 years ago were a lot less than the carbon string from the same supplier. They are still in perfect condition after 100k, which carbon string certainly wouldn't be. I have my doubts whether these without end caps would make a firm connection from the cap screws, for the same reason as the carbon string type won't. Sets for the push-in caps at least have metal end caps on them, what do yours have? If end-caps and they can be scrunched to fit inside the cap holes then the screws should make a firm connection to that.

Coils face downwards when on the inner wing (by 69 according to Clausager), it's said so the oil filling helps cools the HT connection. At the very least it will enable any water to drip off rather than lying inside.
PaulH Solihull

Paul's comment about the coil tower pointing downwards to aid cooling agrees with a dim recollection in the far recesses of my memory, but I can't remember seeing any definitive documentation about that.

When I asked Geoff Allen about it he said ( perhaps tongue in cheek ) that on the V8 he thought it was just to keep the HT connection away from the bonnet which is very close to the coil.

A drawback with the tower down is that the oil can leak out ( yes, seriously ! ). Tightening the screw inside the HT connection stopped the leak, but by then who knows how much of the oil had gone - I suppose I could compare the weight of the coil with a good one, but I just changed it anyway.
J N Gibson

Thanks all for you valued comments. Paul I have just received the leads today through the post and I will check the fittings as soon as my baby sitting responsibilities permit! Thanks for the advice my car wouldn’t be the car it is without this great site!
Dave MGB

The documentation re coil position is in the MGB WSM, under sec B2 "Testing the Ignition Coil". As it is a worst case test, they are specific about how to mount it for testing and they tell you why. In addition to reading the book - now out of fashion - you need to use some brains to figure out that you should mount it in the contrary position for use. That would be connection end down or horizontal with the LT connections also horizontal, so that the internal connections are submerged in oil. Since the oil expands with heat, there must be some airspace, and if mounted "upright" that space would be around the connections.

FRM
FR Millmore

Dave, I wouldn't chuck that old coil away if I were you. I have just recently had a new coil break down on my MG and it took a while to work out what was going wrong. I fitted a new coil and it was as right as rain.

Your old one might be better quality and better in the long run.

Mike
Mike

Hi FRM,

yes I know what you mean about reading the book being out of fashion; if you and I weren't such polite chaps we might begin most replies on these boards with RTFM !

But on the other hand, WSMs were written for trained technicians not for hobbyists who might be new to working on cars so, as you say, there might be some more figuring out to do.

Of course I do have the MGB WSM, but some sections don't get read as I switch to the V8 supplement. If I haven't read that part of the MGB WSM in detail then I expect I must have read the points about coil position and air space for the oil in some general manual several years ago.

Incidentally the WSM for the MGA ( or the edition I have anyway ) has only a check for a fault in the primary winding, no discussion of testing the coil's performance, and no mention of aligning the LT connections for the horizontally mounted coil.

Jim
J N Gibson

Hi Guys
The plug leed sets we get here have little metal pins about 12mm long with them
After you cut your leeds to length you push the pin into the carbon centre core of the leed from the end and then fit the leed into the cap. The securing screw then contacts on the pin giving a good contact to the carbon core. Without the pin the carbon just burns back
Willy

I'm thinking the tripple silicone is the insulation only, they are still carbon based leeds ????
William Revit

The WSM does indeed indicate the coil should point up, but it was changed by the factory from horizontal on the engine mount to pointing down (from almost every picture I have seen) on the inner wing. The WSM talks about an angle of 45 degrees, and by accident or design the inner wing isn't far from that. The WSM also says "45 degrees on the test rig" ... surely we aren't expected to carry one of those around with us as well?

FWIW the Lucas Fault Diagnosis Manual shows the coil fully upright in all cases.
PaulH Solihull

Paul I agree with you and you are always very helpful even if the question has been asked a million times over the years. However in response to the RTFM post from Jim I would like to say RTFQ. In part of my post I clearly said I had seen the MGB ignition coil fitted at both attitudes. I was after general advice from friendly BBS users. Remember the MGB WSM is a book of reference for a wise man and a bible for an idiot!
Dave MGB

Hi Dave, no disrespect intended, my comment was not aimed at your particular questions. I think we just got a bit sidetracked.

We've probably all seen coils mounted at all possible angles and in various locations - in cooling air streams or directly on hot engine blocks. If it was really critical then I expect the manuals would be more definite and not so inconsistent.
J N Gibson

It subsequently occurred to me that the reason the WSM says precisely how the coil should be orientated - for *testing* - is especially for the purposes of revealing a problem with the CB terminal which is probably a known failure mode. It actually says to me that the terminal *should* be covered with oil in normal use, making that failure less likely.

The V8 coil is relatively low down compared to the distributor, the leads from that *are* pressed up against the bonnet.
PaulH Solihull

Exactly what I wrote.

FRM
FR Millmore

I love this--
Now gentlemen I have an old lucas coil and at the joint where the outside of the main/top/insulator piece fits into the barrel it has a little slot/spit hole on the edge.
The QUESTION
Would we mount this coil
1-Connectors down so it spits oil if it overheats
2- Connectors up so it spits air
or
3-Horizontal so that the internal terminals are covered with oil but the spit hole is still on top
Willy
William Revit

Willy -
Gotta pitcher? I never saw one like that. Maybe some genius drilled it, maybe put oil back??
Does oil run out if you invert it? Or is there some sort of restrictor device?
Or it could be a split from some bizarre stress situation.
Is it in fact an oil filled coil? - not all are. That was a later "high output" innovation, subject of some advertising boasts from manufacturers.
The "basic" coils were insulated with wax impregnated paper, and no oil; they tended to get hot and could melt the wax out of the paper, thereby losing the insulating value of the wax (and charring the paper, which sucks as an insulating material). Adding oil was to cool it, but the oil also functions as a dielectric. Possibly PCB oil, since that's what it was invented for. Now top end coils get potted with epoxy.
If it is oil filled and has oil innit, and the hole is really a hole even if restricted, then 3) would be the appropriate mounting.

FRM
FR Millmore

Leaking oil is wrong, whatever. If it's supposed to contain oil and it leaks inverted, then it is faulty. If someone has drilled the top to pour oil in, then goodness know what state the coil is in.
PaulH Solihull

Many thanks for all your comments to my original post. I have now fitted a new top entry distributor cap to my 25D4 distributor along with the silicone leads and a new 12v sports ignition coil. The car now starts first time every time and the engine bay looks a bit better. If anyone is interested I have posted a picture showing the clearance of the dizzy cap from the steering rack. It’s close and looks closer on the photo but still allows full lock without touching or rubbing the lead caps, Job done. Next!

Dave MGB

This thread was discussed between 10/01/2011 and 16/01/2011

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