Lost its spark!

[Village Idiot]

On my first drive of the season, the car started to misfire after a 3 mile drive. Within 2 minutes, there had been a complete loss of power and I parked up, unable to restart the engine. I checked that there was fuel in the float chamber and concluded that I had an electrical problem. During the tow home, I engaged gear with the ignition on, but no joy. The engine would not run on when put back in neutral. I've just checked the LT system and with the LT wire connecting the distributor and the coil removed, got 12 volts when the points are closed, about zero when they open. I think that's how it should be. With the distributor cap off, I can see a faint spark at the points when they open and close (starting handle).

I have one wire between distributor and coil and one wire from the other coil terminal to a harness, which I assume to be earth.

Now for the bad news (or, I think , a red herring). I found a free wire (green/brown?) with a corroded, dirty spade connector on the end. It has 12v when the ignition is on. It comes from a harness in the same area. I don't think it is part of the ignition but it's confusing me. Am I right in assuming that the coil has only two LT wires connected to it?

Any ideas?

[bmcecosse]

Clean the points (although they appear to be working) and try a new condenser. Also suggest you check the HT leads and the rotor arm.. The extra wire is for the oil-filter-blocked warning light - if you earth it an orange light will light up on the speedo......

[mike.perry]

Green/brown should connect to the oil pressure switch, although the wiring diagram says green/yellow.
White/black connects from coil to distributor and white from ignition to coil. Check for spark on both these terminals.
Mos likely fault is coil or condensor.

[Dean]

My points stopped sparking even with the correct gap and power going through them.

Just change them (points and condenser) as you would a normal service. It worked for me.

[bmcecosse]

It's NEVER the coil.........leave it alone.....but do check the connections are clean and tight.

[mike.perry]

I've got a box full of "Its never the coils"[frame][/frame]

[bmcecosse]

Yes - we've been there before -but that's a 'new' coil, and they are hopeless. In fact that coil may very well work - if the casing hadn't been damaged and the cooling oil allowed to run out. My statement re coils (as you very well know!) refers to original colis - not modern replacements.

[JOWETTJAVELIN]

Originals will run for decades.

[Matt Tomkins]

Mavis' original coil went the other week. Replaced with Misty's and she ran like a dream, so bought a modern replacement. I give it a week...
The joy of having 2 cars with parts interchangeability!

[bmcecosse]

The joy of having known GOOD spare parts in the boot cavity..... What happened to the old coil???? Clean all the connections and try it again...

[Matt Tomkins]

The joy of having known GOOD spare parts in the boot cavity..... What happened to the old coil???? Clean all the connections and try it again...

Trust me -- i'm a tight student (scotsman in training ;-) ) -- i've tried everything...

[bmcecosse]

Hahahaha - oh dear - you have been unlucky then.... Sell it on ebay!!

[Matt Tomkins]

Sell it on ebay!!

'Unknown condition, Old stock, Superior quality as recommended by BMC...'

[brucek]

Sell it on ebay!!

'Unknown condition, Old stock, Superior quality as recommended by BMC...'

....one careful owner, never raced or rallied .....

[Village Idiot]

Thanks for your help - especially with the oil pressure switch wire.

I have replaced the condenser and cleaned the points and rotor arm. How can I check a condenser with a cheap digital voltmeter ? (Both condensers may be failed, although the replacement was new.)

I'll have another look today, but feel its either going to leave me stumped or be embarassingly simple.

PS I've seen the correspondence about the coil. It has a resistance of about 3 Ohms across the LT terminals.

[MarkyB]

Does the rotor arm have a rivet holding it together?
This type are very prone to failure.

[Village Idiot]

I replaced the rotor arm with the one I didn't throw away at last year's service. It started! I put the "new" one back in. It didn't.

Both rotor arms have a rivet. Both look the same. I can see nothing wrong with the new one. How can you tell if a rotor arm has failed? What's to fail?

Anyway, thanks for all your advice and I'm glad to say that it wasn't the coil!

Off for a drive in the sunshine now.

[katy]

It's been my experience that when a rotor fails it shorts from the HT part down through the insulating material to the steel shaft that it sits on. If you look at it from the bottom you may see a small carbon track at the bottom of the opening where it sits on the shaft.
You can't reliably check a condensor w/a "cheap digital voltmeter"

[MarkyB]

How can you tell if a rotor arm has failed?

The car wont run when it's fitted
The original non-rivet type are now available in Red plastic as "high performance" items.

[Village Idiot]

Katy is absolutely right. On the flat face inside of the failed rotor arm, right next to the metal spring, there is a rough pit about 3mm in diameter. The spring next to it has been blackened either by high temperature or carbon burning off from the pit. It looks as though there has been tracking from the brass on top through the bakelite to the internal metal spring.

When I looked at it originally, I was looking for a line or a crack. It was only after reading Katy's note that I went back and realised that the pit was not just a bit of dirt. Many thanks.

NOW I know how to tell if a rotor arm has failed!