Different "Engine won't start"

[Ian Anderson]

When I first completed the restoration of my SC (National Rally was at Castle Howard), it always started reliably. After a number of years it would often refuse to start if left for any length of time.

Initially I think the problem was degradation of the "petrol" as discussed in Mike Alfrey's post, however, starting became progressively more difficult over the years. I thought I had a carb. problem as the float chambers seems to be overflowing, but after wasting much time checking fuel pressure and changing float valves, I realised that if you turn the engine on the starter for any lenght of time on full choke. the petrol sits on the choke butterfly and seeps out of the throttle spindle.

I decided the problem was ignition and changed everything apart from the distributor itself. I eventually got the car to start by changing the new Lucas coil for a Morris Minor coil I had been given. This worked for a while, but the problem returned, and now would not start when hot after a run.
Last autumn I thought the car was running OK after re-setting the mixture, and drove round to the local garage but the car refused to start after getting petrol. The garage owner (who used to do Crypton tuning in the days before you needed a laptop) tried everything to no avail.

I thought the coil was rather too warm, and after wrapping it in a wet cloth for a while, the car fired up and ran fine. I know from the Morris Minor club that there is an issue with Lucas coils made in the far east. They are poorly manufactured and often have insufficient cooling oil. Most cars have the coil mounted with the terminals pointing upwards, but Jupiters and Minors have them horizontal. The MM club recomend making a bracket to facilitate the vertical mounting of the coil as this allows the oil to work more efficiently.

I have now done the same to the Jupiter, and invested in a new "Remax" coil. These coils are made in the UK (Birmingham I think) to a higher standard if the advertising is to be believed. It certainly gives a more reliable spark than the old coils, and was only about 50% more expensive. I hope I am not speaking too soon as I have not yet had chance to road test the car, but when I started the car with all new petrol after 7 months , it started first pull. I left it running for about 20 minutes then started it again OK 5 minutes later.

Touch wood!

[Keith Clements]

I too had a similar problem on the Javelin except it would start easily but then after about 5 miles it would die. I too felt the coil and it was hot. Now there may be a few possible issues. The polarity of the spark is incorrect or the dwell is incorrect or the capacitor may be incorrect. Dwell is a compromise between having enough power to get a spark and not heating up the coil. On contact breaker ignition dwell is governed by the points gap, strength of spring and the capacitor. A variable dwell can be achieved with electronic ignition so can produce more power in the spark at higher revs..
I replaced the whole system with a new coil and electronic ignition, but have now reverted to a refurbished standard dizzie set up to my spec. The reversion was more for aesthetics, not because anything was wrong with the electronic system. The same switch back was done on my SA as well. The unit with the mapped dwell and advance is still in the Jup and a spare electronic dizzie is in the boot. The extra wires for it were put into the new loom during the rebuild.
Do modern coils have oil in them? Must open one up. But yes you do need to keep the coil in a good air flow and move it away from where it blocks the radiator.

[Ian Anderson]

Hi Keith
I started the car again yesterday and took it up onto the moors above my house (So I could coast home if the Jup died on me). It ran fine apart from a slight splutter on pick up which the car always had. (Standard 30VM Carbs) By the time I got home, the tickover had reached 1500 revs which is easily sorted. The coil was warmish, but the engine started fine when I tried it after a few minutes.

I spoke to Holden's ignition "expert" before purchasing the new coil, and he said coil overheating is usually down to a poor earth on the engine or distributor, which I could not quite understand. I think the dwell angle, as you say, makes more sense from an energy point of view.

All three coils are in my possession are oil filled - you can hear it if you shake them. The Minor owner who gave me the previous coil now tells me that he changed it to a two coil set up (however that works) as it used to cut out in traffic queues and would not start again until it cooled down!

The Jup "runs on" a bit when hot and always has, but so does the Minor so I assume that this is just down to modern "petrol".

Ian Anderson

[Forumadmin]

Coil-ignition was patented as early as 1908 by C. F. Kettering of the Dayton Engineering Laboratories Company (DELCO). Michael Faraday discovered the laws of electromagnetic induction in 1831 — the ignition coil is a direct application. When a wire and a magnetic field move relative to each other it is found that a voltage (or electromotive force (emf)) is generated in the wire. The voltage induced in the wire depends upon:
(a) the length of the wire in the magnetic field
(b) the relative rate at which wire and field move
(c) the strength of the magnetic field
The magnetic field could be produced by a permanent bar magnet, but in the case of the ignition coil it is convenient to pass current from the battery through a primary coil, the result being a magnetic field. Remember those experiments with iron fillings and a bar magnet that showed the lines of force of the magnetic field? Switching on the current results in the magnetic field spreading. Conversely opening the switch causes the field to collapse. In both cases the magnetic filed moves relative to the wire and so during the very short period of time over which the magnetic field reduces to zero the induced voltage which may be measured across the primary coil reaches up to 300 volts.

This induced emf is not directly related to the 12 V supply; the battery has simply been a means of creating the magnetic field. The switch is the means of rapidly altering the magnetic field
the coils are cut by magnetic force lines as the field either builds or collapses.
A much bigger voltage is needed at the sparking plug so a secondary coil of 20000 turns is wound inside the primary with 300 turns but insulated from it. The secondary winding is subjected to the same magnetic field changes, so it will have the same induced emf per turn as the primary. The result is a voltage sufficient to produce a spark at the plugs.
A current of about 3 amps flows through the primary. One end of the primary is fed from the battery, the other end is joined to one end of the secondary and also the contact breaker, the other end of the secondary is heavily insulated and feeds the distributor rotor and then to the spark plug. Where the electric charge crosses the spark gap to return via the engine and chassis to the battery. The contact breaker too is earthed through some thin wires in the advance mechanism to the distributor body and then it too returns through the engine and chassis to the battery. If either of these earth returns is faulty then the system will not work properly. Similarly high resistance feeds from the battery via fuse box and ignition switch to the coil primary may also cause issues.

The capacitor connected across the contact breaker points prevents sparking at the instant when the contacts open. The effects of such sparking are:
(a) the Induced voltage in the ignition coil is reduced markedly
(b) metal transference from one contact to the other would cause serious erosion

When the contact breaker (or switch) is opened the primary current falls rapidly so does the magnetic flux so both primary and secondary windings will have an emf Induced in them:
(a) only as long as the current is changing
(b) of a magnitude which depends on how fast the flux (and therefore the current) falls

At the moment of opening, the induced primary voltage (300v) will appear across the contact breaker points and current will jump the gap. This is seen as sparking at the points. it follows that the current does not drop instantly, so the magnetic field does not collapse as quickly as it should ...so less spark at the plug.
Just as a bucket will hold a quantity of water, capable of being drained out again, so the capacitor holds electric charge.
When the contacts are just opening, instead of a spark jumping the gap the charge will now flow into the capacitor which quickly develops a terminal voltage, so as to oppose any further charge flow. Thus the primary current drops to zero much more quickly than without the capacitor.

The Capacitor too has to have the other side of its 'plates' connected to the return to the battery but this is via the baseplate that the contact breaker earth side is also on and uses the same fragile wire to the body of the distributor.