Ignition spark after negative earth change

[Bud English]

Capacitors in old radios and other electronics suffer from lack of use and deteriorate over time. I don't imagine radio suppression or ignition point capacitors are much different. They have a limited lifespan whether used or not. Saving those NOS capacitors for future use may be pointless (no pun intended).

[billwill]

Capacitors in old radios and other electronics suffer from lack of use and deteriorate over time. I don't imagine radio suppression or ignition point capacitors are much different. They have a limited lifespan whether used or not. Saving those NOS capacitors for future use may be pointless (no pun intended).

That's mostly so for electrolytic capacitors, they dry out. But it's not so likely on foil & waxed paper type that a car capacitor would be made from.

[Chancer]

Ok its decades since I was regularly changing plugs, points and condensors but back then I serviced and repaired loads of cars as a part time business in order to fund my studies.

during that time I only ever experienced one condensor/capacitor that failed in service which was my own after trying radio suppression on the CB side of the coil so maybe even that was down to me, however several times a vehicle would not start after my service and the problem turned out to be a duff new condensor, eventually I stopped changing them as I could not count on the quality and a few failed within 100 miles which affected my reputation.

fast forward 2 or 3 decades and with the quality of most newly made parts for classic cars I would have very little faith in condensors/capacitors and would choose electronic ignition but with a known good set of points and condensor in the boot for when the electronics fail.

[Concrete-crusher]

Hi I'm still having a problem.

I have now fitted a new coil and condenser and am not getting a spark.

If I measure the voltage on the ignition switch side its +12v with the ignition turned on. With the ignition turned off it seems to be giving an earth. I'm not sure if that's correct but assume it is.

The negative wire to the distributor seems to give an earth regardless of the engine position. ie points open or closed it still reads a voltage if connected to the black lead of my volt meter. However there is no continuity across the points when there open.

The only bit of the distributor that now looks old is the spade connector on the distributor that goes back to the condenser and points connection. It looks a little more than a simple connection as it has a metallic disc on the inside , i'm not sure what function this does.

Any advise welcome.

[billwill]

Sorry, I miss-read your post so what I wrote here was wrong so I've deleted it.

[billwill]

The negative wire to the distributor seems to give an earth regardless of the engine position. ie points open or closed it still reads a voltage if connected to the black lead of my volt meter. However there is no continuity across the points when there open.

I presume by this you mean that you have your black probe lead of the multi-meter connected to chassis or engine metal and your red probe on the negative terminal of the coil. This SHOULD read zero volts when the points are closed and should read 12 volts (approx) when the points are open. If it always reads zero volts either the capacitor has shorted out inside or maybe you have inadveredly connected the flying lead inside the distributor to earth instead of to the flat blade spring of the contact breaker. There are two 'top-hat' shaped nylon washers used to insulate the flat blade spring from the post on which it is mounted.

However there is no continuity across the points when there open.

Exactly WHERE did you put your multi-meter probes to check this?


~~~~~~~~~
On this image, you can just see that the flat blade spring has a nylon insulating washer at it bottom end and top end and that the flying lead connects directly to the spring, underneath the top insulating washer and NOT to the nut on top of the mounting stud.




.....
Sorry if you already knew this and had done it right, but we are starting to clutch at straws here.

This diagram is more detailed:

[bob_rich]

HI again

The voltage on the CB (distributor) side of the coil should change as the engine turns and the points open and close it should be near 1V points closed and battery volts 12V points open. It may be that the insulating washer that secures the points lead and the new capacitor is shorting to earth so the points remain shorted out. this would be my guess as if you have fitted a new condenser the fixing would have been removed and replaced

hope this helps

best of luck

Bob

[Concrete-crusher]

Thanks for the diagram. Yes the connection was shorting out as I had put the terminals the wrong side of the washer.

However having re connected it correctly its still not working.

I notice I don't have a LT wire to earth , also my LT wire from the connection to the spade was looking suspect so I replaced it with a new wire soldered in.

Is there anything special about the LT wires. I notice they are insulated with a cloth like sheath not plastic.

Steve

[billwill]

Are you talking about the wires in the distributor?

Cloth covering is used on wires to make them more flexible than rubber.

Or it might be a higher temperature cloth than rubber.

~~~~

In the diagram above, you can see an Earth wire from the CASE of the distributor to the plate on which the points are mounted and thus to the FIXED contact of the contact breaker.

[Concrete-crusher]

Thank you for advice. Its funny how a simple circuit can prove so troublesome.

You asked how I measured continuity across points. I simply placed the Ohm meter probes either side of the contacts.

I suspect the problem is the connection from the condenser to the points. As I have replaced the condenser I am now going to change the points and replace the LT wires.

Its strange how this happened at the same time as reversing the polarity , when that should not affect it. Maybe not having the earth LT wire as seen in your diagram has something to do with that.

How do I know the type of distributor I have. is it a 23 D 4 or a 25 D4. There's no vacuum advance so I presume its a 23 D4. I can't see any markings , but maybe there at the back out of sight.

Thanks again Steve

[billwill]

You asked how I measured continuity across points. I simply placed the Ohm meter probes either side of the contacts.

That's what I thought, but that will not really trouble shoot the distributor.

You need to connect your ohm meter between the spade connector and the case, with no other wires connected to the distributor. Then see that it is near zero ohms when the contacts are closed and near infinity ohms when the contacts are open.

This would have immediately revealed your earlier wiring error or a shorted out condensor.

If it is always infinity ohms (i.e. open circuit) yet the spade to flat blade spring wiring is correct, that would be because it needs an earth wire from the case to the platform holding the contacts. Without the earth wire I suspect there may be some contact through the shaft and bearings to the case, but it might be erratic.

The wires need to be extra flexible in there, because the platform moves slightly backwards and forwards, depending on engine speed, to cause the advance & retard of the ignition.

[oldelanman]

How do I know the type of distributor I have. is it a 23 D 4 or a 25 D4. There's no vacuum advance so I presume its a 23 D4. I can't see any markings , but maybe there at the back out of sight.

The type, variant and production date are on a raised portion of the body of the distributor on the opposite side to the LT connection......

[tonyabacus]

With ignition switched on 'flick' the points open and a spark should jump the gap, have you checked both the high and low voltage out of the coil, if ok, pull the king lead out of the coil and check the continuity between the end of the lead and the centre terminal inside the distributor cap, which will prove there is no break in the lead. If the coil and continuity checks are good you know you have current into the dizzy and if there is a spark across the points then the contacts should be interrupting the spark to each plug in turn, that leaves the rotor arm as the only other possibility.
Tony

[Concrete-crusher]

Having changed the condenser ,points and LT wire I am now getting a spark. I have ran out of time this week so next weekend I will see if she starts.
Thanks all for advice. particularly the diagram.

Steve