Forum

[Martin]

Perhaps one or two of the
superb electrical men here
can enlighten me. Have three
stock 6V ign. coils for my
early Twin, none which give
end spark despite refurbished
H/T leads, dist-cap & points.
However, when the live points
are snapped with a screwdriver,
all will give 1/2" spark from
dist-cap H/T lead to the motor.

When tested, all give 1.5/2.5
ohms from positive to negative
posts, and visa-versa, but no
reading at all from coil H/T
outlet to either of the side
posts, despite one of the coils
allegedly new. Vaguely assumed
resistance figures from H/T
centre to side posts was how
you determined the polarity in
the first place. Maybe coils
are defunct anyway? Thanxs!
Gordon.

[Edward]

Gordon, if you are getting a half inch spark from the HT lead the coils are not defunct.

[jaffa90]

Not familiar with your bike but if you get a good 1/2" spark when you snap the points open you should get a spark when the cam opens them and closes them at the correct dwell angle.

[Frank]

You would normally expect a reading of 1-3 ohms across the primary winding of the coil between the positive and negative terminals , as you have found. You should also get a reading across the secondary winding between the HT lead connection and both the +ve and -ve terminals of the coil. It will however be a higher value of around 10000 ohms. It doesn't matter which way round you connect the test leads as essentially you are just measuring a coil of wire so it will be the same either way.Given the higher resistance of the secondary coil have you adjusted the scale of your meter accordingly?

[Les H]

As per the three answers above, it would appear you have no faults within the coils. I would have to suspect the way you have assembled or not adjusted the contact breaker correctly. I'm not sure of what you are doing when you say you "snap" the contacts with a screw driver...are you moving them apart or bridging the gap? If you are bridging the gap to create sparks it could mean that the contact faces have dirt on them so they appear to making contact but are not conducting electricity. If the screwdriver creates a spark by separating the contacts then maybe they are not actually being opened by the cam but that would seem unlikely, but not impossible to do set them like this...Another possibilty is that you are adjusting the gap too far away from the points cam lobe maximum lift position and therefore they are never closing when the cam turns to a lower lift position.

[Martin]

Thanxs all for your responses.
Frank, belately did raise the
ohm meter's reading before I
saw your advice. Whilst all the
coils gave approx 1 ohm reading
from positive to negative low
tension posts. the 6V Bosch
coil gave 8900 ohms resistance
from L/T to H/T post, the 6V
Lucas was 6900 ohms, whilst
the new genre 6V of same size
gave a 4900 ohm reading. Les
meanwhile raised some valid
points which I had already
diagnozed with the meter etc.
The 'snapping' meant I quickly
parted the points with a 'driver.
Distributor and rotor is new,
unit is the Lucas DK 82A as
fitted to the early Redditch
Twins. Points bakelite base
may be shorting. Will go thru
it all again when fresh again.
Thank you! Gordon

[Les H]

One final thought Gordon, make sure the distributor cap has the central spring loaded carbon brush in position that transmits the spark to the twin outer spark-lead terminals via the rotor.

[Norm]

Just realised it is the lack of spark not the coils which was the original question, first thing I would look at is the wires into the condensor, bet there is an issue with the insulated washers.