Kaput ignition coil?

[mini5967]

So I have the original coil from my 64 850 project, yer actual Lucas LA12 45113F 8/64 date stamped model, and I was wondering if it was still any good. Stuck the multimeter on it, and got 3.5K on both sides for the primary reading, which seems to be borderline, and 4.3 for the secondary (using the 20K setting on the multimeter). Being a bear of little auto-electrical brain, it's the latter reading I'm uncertain about, even after ages of Googling. Has the beastie still got some life in it, or is it new coil time?

[dklawson]

A lot of aftermarket coils will have 3.5 Ohms on the primary winding so your measurement there does not necessarily indicate a problem. Your 4.3 measurement of the secondary winding (on the meter's 20k scale) indicates 4.3 k-Ohms which does seem a bit low. I think it is more common to find around 8 k-Ohms when measuring between the center (high-tension) coil terminal and either spade connector. However, you measured resistance so nothing has "burned open".

Is this coil bad? Not necessarily. Put it on your 850 and use it for a while. It won't cost anything to try it. Check the spark plugs looking for healthy blue sparks (after fitting a new set of points and a known good condenser). If you have a modern (voltage pulse sensing) tach installed it can provide an indication of coil problems. Failing coils will often produce needle flutters, blips, and bounces on the tach. It's not a given but tach needle behavior can be a good indicator.

[mini5967]

Thank you Doug, just the answer I was after! Slight snag is that the engine is out of the car at present, so using it isn't exactly an option. Best thing to do is to use it on the initial engine rebuild and see what happens, using your advice as a guide. At this point I'm still undecided whether to stay on points or use an electronic module, but to start with I think I'll go with points and take it from there.

[mk1]

Old coils are pretty much universally better than new ones with some of the "premium" modern coils being bloody useless in practice.

I try & use original 60's coils wherever I can. Although NOS are getting very hard to find, good s/h are still relativity plentiful.

As Doug said, the best way to check any coil is to run it.

[mini5967]

Old coils are pretty much universally better than new ones with some of the "premium" modern coils being bloody useless in practice.

I try & use original 60's coils wherever I can. Although NOS are getting very hard to find, good s/h are still relativity plentiful.

Good call Mark, might be a good idea to try and hunt a few s/h ones down in the near future as a back up plan

[iain1967s]

Just measured a 12/66 original HA12 coil.

It shows 3.1 Ohm on the primary and 7k on the secondary using a Fluke digital multimeter.

[111Robin]

I can test coils on my Sun analyzer for output voltage, the resistance test will show a complete failure but testing under load tells the full story as you can often achieve reasonable resistance readings but under load it can be a different story. Not much help I'm afraid , it's another throw away item these days.

[croc7]

If you decide to replace, I really like the Bosch blue coils with epoxy filling rather than oil. Seem to last forever. Look for the ones made in Brazil.