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MG MGB Technical - Dead Condenser

Has anyone had a condenser break down? On my Magnette, which I bought this summer, the nice shiny condenser stopped working completely, meaning the engine wouldn't even start. Using Paul Hunt's tip of bridging the points externally showed that the one in the distributor was dead.

Testing it with a digital multimeter showed open circuit so it looks like something broke inside completely. I have yet to put my analogue multimeter on it.

According to the MGB manual, the capacitance of the condenser should be 0.18 to 0.24 microfarads. Is this a standard value for any condenser? I had a spare but obviously this is now on the car. Getting Lucas parts here is difficult so I was wondering whether I can use any condenser (mounted externally) as a get-you-home spare part.

Mike
Mike

Mike, it seems to be a continual cry. The capacitors or condensors that are available now are rubbish. Here is an excellent article on why that is so.
http://www.britishcarforum.com/tikiwiki/tiki-index.php?page=Condenser%20Failure%20in%20Conventional%20Ignition%20Systems

Buy a job lot and carry a few spares, or better, change to electronic ignition.
Mike
Mike Howlett

After several Chinese capacitor disasters and a failed Pirahna and Jolleys Electronic ignitons I am now using a Boyer Bransden assisted ignition with a NOS Lucas cap still across the points. This means that when you hit a problem, eg on the way to Berlin the earth wire to the amplifier went intermittent,(that fitter should be fired :-)) you just disconnect it and carry on. I fault found and fixed back home in the dry garage. One nice thing is they are availble in +ve earth. My Lucas cap came from someone at the Chesham natter who knows someone , he is in Hemel Hempstead. I could get one if still avaible and mail it to you Mike if you want to try that route. That Magnette of yours is a find. I have a pic of it outside the Hotel, i was pleased to see it as it gave me a hint the satnav had worked, let me know if you want it uploaded
Stan Best

Very common, some failing in as little as a dozen miles or so. There is no reason, given good manufacture, that a condenser shouldn't last the life of the car - or even your life! Several cars it's true, but I've never had one fail in over 40 years. I did have a rush of blood to the head a few years ago and fitted a new cap, rotor, points and condenser with new leads a few years ago, but got away with it. I have heard of people changing them annually as a matter of course - don't!

There are a couple of ignition specialists in the UK, try http://www.distributordoctor.com/distributor_condensers.htm or http://www.simonbbc.com/points, although the latter may only have them as a points and condenser set.

.18 to .24 is the standard MGB capacitor, other cars may be different but I don't know why as that value was retained even when the inductance of the MGB coil halved. I've tried double and half the value on a test rig just to see what happened, and whilst the shape of the HT pulse did vary very slightly when viewed on an oscilloscope it didn't alter the voltage or duration or the visible spark. As long as the old one hasn't gone short-circuit then just temporarily connecting a second condenser will certainly do the trick (assuming the internal one *has* gone open-circuit and it isn't a different problem altogether), connect between coil terminal that goes to the distributor and earth.
PaulH Solihull

'Usually' (and I emphasize 'usually') a capacitor (condenser) will either fail in the first few hours of use, or it will last forever. Prior to installing a pertronix ignition, whenever I replaced the points in our cars, I would check to see if there was any excessive metal transfer on the contacts. Metal transfer from one contact to the other indicates a capacitor of the wrong value for the circuit it is working in and since the capacitors used for ignition circuits have a tolerance range of 20%, there is quite a wide latitude of actual capacitance. If there was no metal transfer, I would leave the existing capacitor in place. The bottom line, I never replaced the capacitor in any of our cars and never had one fail. On the other hand, I did replace the capacitor in our daughter's GT because of metal transfer and the new capacitor failed in about a week (the replacement capacitor has lasted for many years). Cheers - Dave
David DuBois

if you are having problems with condensers make yourself one of these, crocadile clip to earth and cable to CB on the coil, it will get you home.A.T

andy tilney

Andy, that is exactly what I am intending to make, just that I will use a non-Lucas condenser which can be bought off the shelf here in Berlin. Although they're not one size fits all, I get the impression that the capacitance is always roughly the same.

Dave, how did you observe the metal transfer? How long was your test time?

Stan, I'm going to try some of the local Bosch / Beru specialists here in Berlin to see if there is a German made equivalent. The Lucas distributor was fitted to so many vehicles, it must also be on their parts lists too.
I'd love a copy of the picture of the Magnette, if you could send it to me at mike (at) standring (dot) de that would be great!

Mike
Mike

This thread was discussed between 05/10/2010 and 06/10/2010

MG MGB Technical index

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