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RE: No start. - Ray White - 16-03-2025
(15-03-2025, 07:01 PM)John Cornforth Wrote: You should be able to measure points resistance on the 200 Ohms full scale range. Check the meter first by shorting its two probes together. The live feed to the coil needs to be disconnected for this test. Measure from distributor LT terminal to distributor body first, then from distributor LT terminal to the engine block to check that the distributor body is properly earthed. With manual advance/retard distributors there is a moving joint, so contact can sometimes be unreliable unless a "pigtail" is added from distributor body to engine block.
If the points really were 0.05 Kilohms (50 Ohms) the primary current in the coil would only be 0.12 Amps, which doesn't tally with your 3.9 Amps reading. Out of curiosity, how did you measure the latter ?
With 6 volts supplied to the coil and distributor.
Using 200 OHMs scale from LT terminal to dist. body I am getting 58.
from the LT terminal on dist. to head stud I am getting 68.
With 20Amps selected (and test lead changed over). With points closed I hold one probe to fixed part and other to moving part. Reading zero until I open the points and then it reads 3.5.
From the above tests can it be ascertained where the fault lies?
RE: No start. - John Cornforth - 16-03-2025
Hi Ray
It's always difficult to ascertain someone's electrical knowledge, but as you are getting odd results here's how I would test things.
Set the test meter to a DC voltage range that can measure 6 volts
Connect the black meter probe to battery negative (negative earth assumed) ideally with a hands free clip of some sort, and leave it there.
Remove the distributor cap and rotate the engine till the points are open
Turn on the ignition, and using the red meter probe measure the DC voltage at the coil switched supply terminal, the coil contact breaker terminal, the terminal on the side of the distributor, the distributor metal body and the engine block. Note down these five voltage readings which I will call A,B,C,D, and E
Now rotate the engine till the points are closed, and repeat the above test noting down the five new voltage readings which I will call F, G, H, I and J
Turn off the ignition
The readings I would expect to see are:
A 6.5 Volts
B 6.5 Volts
C 6.5 Volts
D 0.0 Volts
E 0.0 Volts
F 6.0 Volts
G 0.5 Volts or less
H 0.5 Volts or less
I 0.2 Volts or less
J 0.0 Volts
There may be some minor variation, but nothing too far adrift from those values. Let us know the results !
P.S. The technique works for positive earth, but the meter will register negative voltages which is not a problem for a modern digital meter. If using a moving pointer style meter, swap red and black leads.
RE: No start. - Ray White - 16-03-2025
The car is negative earth.
As I cannot easily use the handle (my Swallow has the hole in the rad shell blanked off) I will have to either turn it on the starter,,, put it in gear and rock the car,,, or jack up one side and turn the back wheel... to do the points.!
I have an A7 friend coming over tomorrow so all is not lost.
RE: No start. - Ray White - 17-03-2025
(16-03-2025, 08:40 PM)John Cornforth Wrote: Hi Ray
It's always difficult to ascertain someone's electrical knowledge, but as you are getting odd results here's how I would test things.
Set the test meter to a DC voltage range that can measure 6 volts
Connect the black meter probe to battery negative (negative earth assumed) ideally with a hands free clip of some sort, and leave it there.
Remove the distributor cap and rotate the engine till the points are open
Turn on the ignition, and using the red meter probe measure the DC voltage at the coil switched supply terminal, the coil contact breaker terminal, the terminal on the side of the distributor, the distributor metal body and the engine block. Note down these five voltage readings which I will call A,B,C,D, and E
Now rotate the engine till the points are closed, and repeat the above test noting down the five new voltage readings which I will call F, G, H, I and J
Turn off the ignition
The readings I would expect to see are:
A 6.5 Volts. ------------------5.97
B 6.5 Volts ------------------5.97
C 6.5 Volts. ------------------5.98
D 0.0 Volts. ------------------0.00
E 0.0 Volts. ------------------0.00
F 6.0 Volts. ------------------5.29
G 0.5 Volts or less ----------0.17
H 0.5 Volts or less ----------0.15
I 0.2 Volts or less -----------0.07
J 0.0 Volts. ------------------0.00
There may be some minor variation, but nothing too far adrift from those values. Let us know the results !
P.S. The technique works for positive earth, but the meter will register negative voltages which is not a problem for a modern digital meter. If using a moving pointer style meter, swap red and black leads.
The battery is now on charge.
RE: No start. - Ray White - 17-03-2025
Now the battery won't accept a charge ...so I'm fed up.
RE: No start. - John Cornforth - 17-03-2025
Hi
Some "High Tech" chargers won't co-operate if the battery is too far discharged
Try an old fashioned one if you can. Once you get a bit of charge in the High Tech one may perform.
If you can't get an old fashioned one, even a 12 volt car battery via a 6 volt headlamp bulb (to limit the current) would do at a pinch.
RE: No start. - Ray White - 17-03-2025
My multi meter is pretty ancient. It is working O.K.
Having fiddled about with the battery charger, it is now reading 6.1 volts.....so maybe it will be O.K.?
RE: No start. - andrew34ruby - 17-03-2025
(17-03-2025, 03:18 PM)Ray White Wrote: My multi meter is pretty ancient. It is working O.K.
Having fiddled about with the battery charger, it is now reading 6.1 volts.....so maybe it will be O.K.?
6.1 v isn't really enough for the battery. Charge it some more if you can.
With nothing connected I would be happier with 6.4 v.
RE: No start. - Ray White - 17-03-2025
She runs!
I had a visit from a friend who knows his way around an Austin 7. He noticed that the HT lead - although screwed into the coil tower - was not reaching the bottom. He made up a new end with a brass washer and managed to get a spark.
My sincere thanks to everyone here. I can now enjoy driving Trundles around the neighbourhood again.