Coil questions.

[arcturus]

Hi, first of all is there any way of testing a coil. Secondly, I am considering removing the coil (if defunct) from the holding bracket, if possible with a view to modifying the bracket to accept a standard coil should I have any more coil problems. has anybody tried this? Any thoughts or suggestions would be appreciated.

[Army]

A coil is a simple beast. You have a low tension and a high tension side - the resistance of these windings are usually specified in the work shop manual. Traditionally these things are oil filled and ideally there shouldn't be continuity between the low and high tension sides...

There are several "helpful" videos on youtube such as this one

https://www.youtube.com/watch?v=h8vSwfnX3Xc

(Didn't actually watch this one just found a link for you - if it is gobbeldy gook move on to the next one)

As for mounting - hmmm - I'd stick with the original one for the sake of convenient HT lead length

A coil should be much like an operating system - you shouldn't notice it - I get the feeling you're having other trouble

[arcturus]

I think that you have misunderstood what I am asking. In the event of the coil packing up finding an original replacement is extremely difficult.Six volt in my case. I was fortunate that I had a spare coil/switch set up There for my suggestion, as a way of keeping the original appearance with coil mounted on bulkhead would be to remove the original coil from it's mounting bracket if possible and insert a a new up to date coil with two terminals showing. Just wondering how difficult that would be and has anybody done that. The fixed armored cable coil/switch set up can cause problems.

[Ron Kwas]

Arcturus;

I've never done this, but I do remember reading a thread somewhere where the original armored Volvo coil assembly was cut open and the failed internals were replaced by a replacement coil (maybe Bosch Red IIRC) ...I believe this was a 12V arrangement...a careful OD measurement would have to made first...the Bosch Red coil apparently fit nicely inside the original housing...I'll see if I can relocate the thread...

Cheers

[Army]

Originally Posted by arcturus

I think that you have misunderstood what I am asking. In the event of the coil packing up finding an original replacement is extremely difficult.Six volt in my case. I was fortunate that I had a spare coil/switch set up There for my suggestion, as a way of keeping the original appearance with coil mounted on bulkhead would be to remove the original coil from it's mounting bracket if possible and insert a a new up to date coil with two terminals showing. Just wondering how difficult that would be and has anybody done that. The fixed armored cable coil/switch set up can cause problems.

I hope the testing suggestion was useful!

As for finding replacements - perhaps a bit of skulduggery is needed? If you search on the interweb for "6V coil classic car" you get several options. Whether these aftermarket things will fit in the existing holder, however, I do not know but there seem to be several out there priced at about the 20 quid mark which might be worth a gamble - sellers might even be willing to measure things before they box them up for you!

[arcturus]

Ron, I measured the resistance as indicated in the u tube video and obtained readings of 1.7 ohm between +&- contacts and 6.35 x 20K between - and HT. would that be in the range for 6volt coil?
Is the u tube a bit simplistic and is there more to it?

[Ron Kwas]

arcturus;

I'm just not certain, having never measured a 62V OR a even a 126V coil, but indeed there is not much else to measuring... Measuring with the DVM takes place with a very low voltage battery within the instrument, so there is no chance of a high voltage breakdown, and one would never find this (most common) mode of Ign Coil failure with the DVM...but for the purposes of determining if your coil is suitable for your 6V application, the best way to do this would be to have someone make the measurements on a confirmed 6V coil and post R values, particularly for the Primary (the critical one!), and compare it with yours...

As a number of commenters on the vid noted, I couldn't watch the entire 20 min either...too painfully slow...I am certainly verbose also, but (I hope, and try to be!) only to the extend necessary to make my info and presentation absolutely clear and useful...

Good Hunting!

[arcturus]

Nothing ventured, nothing gained I thought so, after ten min's work with an old fashioned hacksaw!
A good start. a bit of fetling, an new six volt high performance coil, solder a wire onto the ignition switch and "hey presto"

[Pigeon]

Originally Posted by Army

ideally there shouldn't be continuity between the low and high tension sides...

Ideally there SHOULD be! One of the LT terminals (theoretically should be "SW" but I've never bothered to check this on a real one) is common to both windings. This is how the return path for the spark current is provided. It would be possible to make a coil where the cold end of the HT winding is earthed through the case, but it is rarely if ever done that way; it certainly isn't here.

Originally Posted by arcturus

Ron, I measured the resistance as indicated in the u tube video and obtained readings of 1.7 ohm between +&- contacts and 6.35 x 20K between - and HT. would that be in the range for 6volt coil?

That primary resistance is in the range you'd expect for a 6V unballasted coil, or for a coil for a ballasted 12V system. A 12V unballasted coil would be about twice that.

Secondary resistance doesn't tell you much. As long as it is in the tens of K range that's as close as a multimeter will get you to an "OK" indication. (A low resistance, or a complete open circuit, are both "not OK" indications.) Yours is "OK".

To test a coil... simply wire it up to a battery and condenser, and stuff a piece of wire down the HT terminal with the other end an inch or so away from an LT terminal, then use something like an insulated pair of pliers to bridge and unbridge the condenser, and see if you get a decently long fat spark out of it. (Do the same with a known-good coil to obtain a working definition of "decently long fat".) Note that voltages of a few hundred are present even on the primary side, hence the use of insulated pliers.

It could be argued that there is a risk of damaging the internal insulation when seeing how long a spark you can get, but I've never managed to do that even with prolonged abuse.

[Ron Kwas]

Pigeon has it right of course...Primary and Secondary are internally connected, as shown here on right (left is the typical coil with ballast resistor):

...I was just unsure about the resistance to be expected...

Cheers