TR2/3/3A Coil against hot engine?.....relocating the coil?

[karls59tr]

I've seen the coil relocated to the fender well on a few TR3's. I was wondering how engine heat would actually affect the coils functioning if at all. What are the symptoms of an overheated coil?

 

[Sarastro]

I've always been concerned about this (although not concerned enough to relocate my own!) The engine block is not a good location for the coil. It's true that the coil is offset a bit from the engine block and there is plenty of air circulation, and the clamp probably is not a great thermal conductor. But I still am not thrilled with it. At some point, when I think of it, I will check it with an infrared thermometer and see just how hot it gets.

I'd expect symptoms of an overheated coil to be the same as any other coil failure.

 

[CJD]

Heat is bad for any electronics. On the other hand, if relocated to the fender, you are then losing your high tension ground directly to the engine block. The high tension sparks are then passing through your engine to frame to body groundings. It will work, but I don't see enough of an issue with heat to make relocating worthwhile?!? After all, it is still sitting in the heat blown from the radiator.

 

[mrv8q]

Whether it’s original or not, the coil on my ‘3 has an August ‘59 date. Not much of a worry in my book.

 

[mctriumph]

I like to isolate it with a fiber washer,but then the bolts leak oil( as they are tapped into the lifter well).
Have to be sealed with Loctite. and seems to make no difference. But I had one fail once years back
I just thought the factory had not installed enough sparks in the thing. They NEVER fail if the spare
coil is in the boot!
Mad dog

 

[Popeye]

Like mad dog stated, a fiber washer makes a great thermal break. I don’t have one, but easy to do next time I’m in there.

No matter where it is mounted, the coil is in the hot engine bay. I suspect it is pretty breezy when driving, so perhaps the airflow is enough to keep it below its “critical” temperature?

 

[JHaydon]

A few small data points

Coils generate their own heat. Likely not as much as the combustion in the engine does, but then the outside of the engine is not as hot as the insides of the cylinders. I mistakenly left an ignition switched on for an hour-ish (engine not running) and the coil was too hot to touch. But it still worked.

Bentley mounted their Lucas coil on top of the radiator. I've overheated that car pretty well in Texas heat, with no signs of coil damage.

I had a Bosch coil fail on the racecar, which was fun (luckily it was the last lap of a practice session). It acted exactly like the car was running out of gas: it would accelerate happily but as it approached redline it would suddenly slow as if the throttle had closed. Shift to the next gear and it would accelerate again for a bit, then slow. I believe that the half-second that it took to shift gears allowed the coil to cool enough to give a few more seconds of sparks. FWIW, the coil was mounted on the firewall in that car. I do not know if a coil can recover from that. I wasn't willing to take a chance.

I recall seeing a major coil overheating incident during a NASCAR race once -- the top of the coil (located in the cockpit) blew off, spewing the oil filling. I don't recall what type of track it was, but NASCAR "generally" runs more or less full-throttle, full-time, in one gear. Running below redline generates less heat than running at full throttle.

 

[mctriumph]

My one failure in the last 50 or so years, was a Lucas gold. It had done fine from coast to coast,
and was 12years old, but just failed out of the blue about 30 miles from home one day.
Naturally I had foolishly cleaned out the boot and set aside the spare......
Mad dog

 

[CJD]

That's Murphy for you! I have carried spares for decades, and the minute I quit bringing it, I will need the part.

 

[jimmyr]

There is no ground associated with the coil body so it does not matter where it is mounted. The secondary from the coil is grounded via the points when they close also providing the ground path for the coil primary too.

 

[Sarastro]

Curiosity got the better of me and I measured some temperatures when I returned from a moderately long ride today. The engine block was 190F at its surface. I couldn't measure the temperature at the coil body, as it was reflective and I was using an infrared thermometer, but the cap (black plastic) was 140F. Not scary hot, I think.

 

[CJD]

"There is no ground associated with the coil body so it does not matter where it is mounted"

Deja Vu all over again!!