Using carbon HT leads with acorn caps...

[Ruairidh Dunford]

This is very helpful Howard - thank you!

[A G Wood]

Done it heaps of times Ruairidh!
Back in the dark ages, "carbon" HT leads were available as a universal kit in this country. The HT lead was supplied by the foot, the distributor end split brass washers were secured to the lead by a tiny brass screw through their center screwed axially into the "carbon" core of the lead. The other (spark plug) end had the core bared and folded back over the length of the lead before crimping the terminal, making sure the core was on the solid side of the crimping i.e. not by the split- at least, this was the official method. It was considered better practice to make up a small U  from either a piece of 1/16 brazing wire or a paper clip, push one leg of the U up into the center core, position the other leg over the insulation along the axis of the wire and crimp as previous.
Edit: The screws were threaded all the way to the head like woodworkers 'hinge screws'-I would think a modelers' supplier would have them.

[AustinWood]

The leads we had were made up and had the push-on fitting for the spark plug in place. The rubber sleeve was left over from our SM restoration. These are high performance leads and are larger in diameter than standard ones. A bit tight in the acorn but that's better than loose as standard HT lead would be.
Note: The original split washer was used in the acorn end.

   

   

[John Cornforth]

Hello all

I think several termination methods would be successful as long as there is both an electrical and a (vibration proof) mechanical connection. The acorns rely on mechanical connection via the copper wire, and I fear that the alternative of just poking a short wire up inside wouldn't give the same strength. I do remember fittings with a screw thread, which ought to give a better grip to the inside of the insulation. Maybe a tiny diameter but fairly long self tapper would do the job.

Traditional carbon leads were generally reckoned to have a limited lifespan before they broke up inside. Inductive leads (mid-sixties onwards) have a tiny spiral of thin wire wrapped around the inner core, they seem to last indefinitely. Termination methods are the same as for carbon.

An alternative is to keep the copper wires but fit discrete supresssor resistors/supressor caps at the plug ends. Usually about 5000 ohms. This is the method I use and it seems to provide enough suppresssion for "modern electrics" onboard equipment to function properly. I chose 4700 ohm 2 watt resistors soldered to the cable and the brass spade terminals. The spaces were filled with PTFE plumber's tape and the whole lot covered with adhesive lined heatshrink. This setup has worked for the last 15 years.

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Photo to go with post above:    

[AustinWood]

We have had no problems with copper wire inserted into the lead. In fact it takes some pull to get it out again.
Personally I wouldn't tie HT leads together. There can be considerable induction between the leads. If one plug fails to fire the induction between the leads causes other plugs to fire at the wrong time.
It was very instructive watching the distributor test rigs running when I worked at Crypton. This has spark plugs, a coil and the distributor under test mounted on a rig. The distributor is turned with a motor. Any bad or disconnected plug in the system disrupts the firing of other plugs.

[Ruairidh Dunford]

Thank you everyone - this is all very useful to me.

[Peter Clayton]

I recall fitting new H.T.leads to engines back in the seventies . We had a Lucas fitting box full of the different types of ends, Split washers, countersunk woodscrews, copper pins in an uneven "u" form. Straight and angled push on ends for plugs and distributor cap. Threaded coil and dizzy cap acorns, Inline and plug cap suppressers
, spare distributor carbon brushes and springs. I/d love that box now, but I expect  like a lot of kit, binned by an enthusiastic parts manager.

[dickie65]

It looks like everyone has missed the obvious.
Has anyone tried the screw in suppressor that fits into the stock acorn thread. I have some of them somewhere, you just unscrew the acorn then screw in the suppressor then screw the lead back in, I think you can fit just one into the coil lead.
I remember back in days of valve TVs that we used to sneak dads 1933 Box just outside our neighbours house when he was watching the TV rev the engine a bit and watch his picture get scrambled by the interference, he would then start to fiddle with the TV so we would stop the engine, as soon as he sat down again we would repeat the process. Needless to say suppressors were not fitted.

[Ruairidh Dunford]

I want it to look stock Richard. The suppressors you mention would not help in that respect, thanks for the suggestion however.

[John Cornforth]

Hi

Re the bundling of leads together, the rubber rings are as per Austin factory photos from the 1920's and 1930's. They lend extra support to the wires, and I have had no problems with misfiring.

I have seen 6 cylinder engines where the factory plug leads are run alongside each other in conduit, with apparently no ill effects. Presumably the insulation must be up to scratch.