Replacement of Lucas HA12 with Lucas SA12 Coil

[Martin AH 3000 MK III Phase 1]

Hi,

My BJ8 has as a standard factory-fitted Lucas HA12 coil. I managed to buy a Lucas SA12 performance coil and want to install it in my Mark III. Does anybody have experience with this type of coil? Is there any benefit?

best regards, Martin

 

[gonzo]

If the primary coil measures 3 ohms, then all should be well. Install and enjoy. True measure of a good coil is longevity and reliability. Gonzo

 

[Patrick67BJ8]

If the primary coil measures 3 ohms, then all should be well. Install and enjoy. True measure of a good coil is longevity and reliability. Gonzo

Plug gap change required?

 

[Bob_Spidell]

Short answer: No, but you won't get the (alleged) benefit of the 'hotter' coil.

Plug gap determines the voltage required to jump the gap (coil secondary voltage stops increasing as soon as the spark jumps the gap--it becomes essentially a short circuit). More voltage, theoretically, results in a hotter spark, hence with 'hotter' or 'sport' coils you can increase the plug gap to produce a stronger spark (not necessarily useful in most applications, but with high-compression, high-revving engines they can help at the margins). A higher-performance coil allows an increase in plug gap; 'book' gap is 0.025", I run 0.28" in my cars with stock coils and Pertronix Ignitor. I would start with 0.030" and increase until missing occurs, then back off a couple thou. Honestly, you aren't gaining much if anything with a hotter coil in a stock Healey engine. With a larger gap you'll probably need to check and re-gap the plugs more often as the terminals erode over time (why you can do fewer tune-ups with platinum or iridium plugs).

ps. Gonzo is correct; my BJ8 has its original coil and is running strong at 215K miles.

 

[Martin AH 3000 MK III Phase 1]

Thank you Bob for your professional expertise! I understand now that it does not make much technical sense changing to the perfiormance coil SA12, especially when keeping the spark plugs as these are which I certainly want to. I do have absolutely no problems with my BJ8 but operated a replacement coil for the last 20 years. I started recently buying genuine spare parts to replace those few "new" parts that aren´t original but replacement parts. I recently managed to buy a used HA12 in seemingly good condition but did not test it yet due to the season break. However, I came across this nice SA12 in unused NOS condition and find it pretty cool. I want to install it as it is an extra from the time which meets the philosophy of my enthusiasm, however I want to be sure that the hotter coil does not do any harm to the engine, electrical circuit or whatsoever and will not show negative sideeffects.

Would you say that it is without any risk installing the SA12?

Best regards, Martin

 

[Bob_Spidell]

The only risk I can think of--and it's pure speculation--is that, in order to produce the extra voltage the windings may be smaller and the insulation less robust so longevity may be reduced; but I have no data whatsoever, and it's probably moot due to the way most Healeys are driven. Lucas sports coils were all the rage a while ago and I heard, anecdotally, of some failures but that's true for old car repops in general (many/most made you-know-where). I can attest that many CoP--'Coil on Plug'--components are known to fail often, esp. earlier ones. If you've seen one, they are considerably smaller than the old, single, beer can-sized coils yet have to produce as much, if not more voltage. VW had many issues when they first went to solid state ignitions, and I've replaced, so far, at least 10 of them on my 2000 Lincoln LS, which has a Jaguar 3.9L V-8. When they failed they would induce a voltage spike on the circuit to the ECU and, essentially, knock it unconscious. To be fair, the coil failures were often caused when oil leaked into the plug wells when valve cover gaskets failed on DOHC engines (which also happens fairly regularly).

ps. Thanks for the compliment, but I'm not a professional mechanic, but I was taught by a former auto shop teacher (my father). My former profession was software engineer, but I taught myself basic electronics along the way. I will say that is a cool-looking coil.

 

[Michael Oritt]

It's red so it must make the car go faster!