Pre-war ignition coil

ian Howell · Post by **ian Howell** » Wed Jul 18, 2007 8:10 pm

So THAT'S where mine came from!

Apart from 'spike' protection, what about the leads themselves!

I much prefer to leave anything above 240V to some braver soul.

This from 'Ten commandments of electronics' that I got years ago: -

No.4 "Take thou care thou useth the proper method when thou taketh the measure of high voltage circuits so thou doth not incinerate both thee and thy meter, for verily, though thou hast no part number and can easily be replaced, the meter doth have one and its loss bringeth much woe upon the Supply Department".

So thou hast been warned!

Tony Fearn · Post by **Tony Fearn** » Fri Jul 20, 2007 10:40 pm

Now, would you believe it!

After all this sagacity regarding the ins and outs of the 'simple' method of producing a "nice spark" where it should be, and whether or not pos is neg or 't'other way round, I have had need to clear out part of the accumulation of decades in the loft.

Now don't go to sleep just yet.

(Believe me, this won't be a Leo saga, although I have enjoyed the J.K.Rowlingesque missives that have recently graced our illustrious website, even though I personally need TWO toolboxes to house all the necessary hardware.) - NOT!

I came across one of the Jowetteer magazines that I took to Beaulieu for our inaugaural stand (239) to show the interested public what the Club was all about. This is Volume 27 Number 8, a sample of the mag that was edited by the one and only George Garside of JowettTalk fame back in August 1982, when he and Dave Fox were joint editors, month about.

Now I know that my long term memory is usually spot on, but I had forgotten that Ben Hicks, in this 1982 edition of the Jowetteer had already broached the subject under the heading 'Electrickery' on pages 10 and 11.

That of course was 25 years ago. Many of our Club members won't have access to Jowetteer mags. of this age, so I've scanned it, and hope to add it to my album very shortly.

It covers:- "Positive and negative earth electrical systems and sparking plug polarity", which is why my opening sentence is as it is.

JAVELIN/JUPITER owners might like to have a look at my scan of page 12 of the same publication if they are interested in a 'pushrod locking plate' with diagram and text.

Tony.

Keith Clements · Post by **Keith Clements** » Sat Jul 28, 2007 10:21 am

Simple test. Use lead (carbon) pencil with tip held in gap between the HT lead and the plug cap, with plug earthed of course. It is best to have plug out of its cylinder so you can see the spark between the normal gap and the gaps betwen the HT lead and the pencil and the pencil and the spark plug. When I say held suggest using insulated pliers!

A spark should be seen between all three gaps; but the spark from pencil to plug should be flared if the polarity is correct. If incorrect the flare will be from pencil to HT lead.

If incorrect, reverse connections on coil either SW/CB or +/-. For positive earth the + would be connected to contact breaker.

If this has been incorrect for a long time, the earth electrode on the plug will be worn away. The plug is designed to wear on the central electrode which is made of suitable material to reduce transfer of atoms. In addition electrons leave the hot central electrode more easily than the cold earth electrode and the centre material is chosen to enhance this desire to leave when given a jolt up the backside by 30000 volts. I should think the pointed shape also helps to concentrate the voltage. (AKA lightning conductor)

Keith Clements · Post by **Keith Clements** » Sat Jul 28, 2007 10:55 am

Another tip:
Examine contact points. If there is a pit on one contact and a pile on the other, this is normal. The pile may be removed with fine emery cloth. Do not emery cloth the pitted contact as this removes the special coating. Alternatively fit new points!

If the points are blued they have become hot due to a defective capacitor or coil.

If the points grey all over this may be due to weak spring or too small gap.

If blackened this is due to oil or grease.

Setting points may be done with feeler gauges; but is better done with a Dwell meter. Not sure whether dwell was ever defined on pre-war cars; but a good starting point is 60% of the time the points should be closed so as to build up energy in the coil. That translates to 108 degrees on a two cylinder or 54 degrees on a four cylinder. Note changing dwell also changes crankshaft ignition timing so reset this after doing dwell.

Keith Andrews · Post by **Keith Andrews** » Sat Jul 28, 2007 10:06 pm

If there is a pit on one contact and a pile on the other

Ideally there should be no pitting or build up on the points
This is also a sign of a condensor crook or of the wrong capacidence.
As to the desposit being on the hammer or anvil, the capacidence can be adhusted up or down, from memory deposit on anvil means lower on the hammer means increase..
Also relocating a coil, and changing the length and/or size of wire will also cause increased pitting of a lessor extent to incorrect capacidence

Keith Clements · Post by **Keith Clements** » Sat Jul 28, 2007 10:26 pm

Where the deposit is depends on polarity of chassis, atoms migrate to negative. If the capacitance does affect then this must be due to dynamics of the coil energy versus the capacitor's energy as it bounces to a balance when points open. In essence the CB contact must go negative because of back EMF so sucking electrons from the chassis. Free electrons actually flow from negative to positive; I guess the atoms flow the opposite way!