What cooks a coil?

[mikeyb]

Non Triumph question this one  . . .  Range Rover started misfiring again the other day, suspect another coil is on the way out.  It was rather hot to touch in relation to everything around it.  

It's the correct voltage and the +/- terminals are connected to the correct cables.  

What causes a coil to get hot and presumably break down in this way?

Cheers

Mike!

[spitty71]

Long shot, but check it has the right rotor arm and cap fitted, I bought a car once and it started misfiring soon after due to wrong parts fitted- result was a huge gap between rotor and cap and caused the coil to burn out.

Steve

[Wheelman]

Check the ballast resistor.  It should only be by-passed during starting, otherwise it will get hot.

[Silvery]

Is it horizontally mounted?

There seems to be quite a few people having problems with new coils being mounted horizontally (as is common on many cars) and burning out - The theory is they simply don't have enough oil in them to properly cool the windings when positioned anything other than upright.

[mikeyb]

Thanks guys.  Cap and rotor arm have been changed previously - identical to the ones taken off and to the one on the Wedge V8.

Ballast resistor I'll look into - not sure if it has one - but if it had failed, I would not expect the car to run at all, right?

The coil is indeed horizontally mounted.  Interesting point that.

Dead annoying - in years of multiple triumph ownership, I've never ever had a coil go!

[rotoflex]

My friend Pierre pointed out to me that if you're leaving the ignition on without the car running for long times for things like checking electrics, etc., you should disconnect the lead to the coil as it will also stay energized.    Without interruption by the points & discharge, the coil gets mighty hot & obviously accelerates its deterioration.

[bodders1]

MikeyB wrote:

Ballast resistor I'll look into - not sure if it has one - but if it had failed, I would not expect the car to run at all, right?!

...unless it has already failed and a previous owner has simply bypassed it as a "temporary" fix.  This would definitely give you a hot coil and shorten its working life.  Check to see if the coil is a 6v or a 12v coil.  If 6v, measure the voltage on the + terminal with the engine running - 6 to 8 volts good but 12 to 14 volts BAD.

[thescrapman]

Bit of extra info.

The original (During Mikes ownership, but not to the RR) coil that lasted many years was labled 'For Electronic Ignition'

anyone know what that might signify?? Different voltage or resistance??

Replacements haven't been labled as such.

Cheers

Colin

[GTRoger]

I know Bosch does 3 different universal coils.

one for points, no ballast resistor
one for points + ballast resistor
one for electronic ignition

So there is a difference. A coil is not just a coil. Can't remember the difference in spec between them.... neither can explain the technical background.