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Blown Condensors ??

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Blown Condensors ??
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  This topic is about my 1980 MG MGB
rustypitbull Avatar
rustypitbull Mike S
Scotch Plains, NJ, USA   USA
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1980 MG MGB
1980 MG MGB
Just had my 3rd condenser go bad in the last 3 months? Any idea what could be causing this? Switched from the stock coil to the Intermotor sports coil from Moss over the summer, but nothing else has changed. Car is a 1980 MGB, but with a 1968 engine.

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ohlord Avatar
ohlord Platinum Member Rob C
A tiny Island off the coast of Washington State, N.W., USA   USA
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1957 Land Rover Series I "EYEYIYI"
1957 Land Rover Series I "OVRLND"
1971 MG MGB
1971 MG MGB "Bedouin 2"    & more
What distributor and plug gap
What ohm coil
Are you using the new improved less prone to failure condenser



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benhutcherson Avatar
benhutcherson Ben Hutcherson
Maryville(St. Louis), IL, USA   USA
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Somewhere or another on the internet, there is a write-up that was made for A-H Sprites but is equally applicable to our cars especially since they use a very similar distributor.

Basically, there was a rash of bad condensers going around for a while that would give intermittent failure and dissection of them showed that the insides were basically "rattling" inside the can.

I THINK the problem has been mostly fixed, but to me after reading that any condenser with an orange wire probably at least bears scrutiny.

It's also worth mentioning that there is nothing magical about the Lucas condenser. If you don't mind the aesthetics, there are options from other vehicles that can easily be mounted to the distributor body or even the ignition coil rather than inside the distributor. I don't know offhand what the rated capacitance of our condensers is, but I'd almost be tempted to fit a tantalum or the like capacitor to the ignition coil. I'll try and see if I have a Lucas condenser either in my office or out in my tool box, and if so I'll measure it.

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garyd Avatar
garyd Gold Member Gary Dabrowski
Naugatuck, western Connecticut, USA   USA
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1957 MG MGA 1500 "Long Gone"
1970 MG MGB GT
1974 MG MGB
1975 MG MGB
Mike;

FWIW, last year I purchased two condensers from the local auto part place. Both were found to be "bad", misfires; crappy running. I subsequently purchased a few of the "good ones" from Jeff Schlemmer at Advanced Distributor. The car has been happy as a clam since then, runs the way it's supposed to. Well worth the money spent.

Here's a little reading material on the subject.

http://www.mg-cars.net/mgb-technical-bbs/dead-condenser-2010100508243917941.htm
http://www.mgexp.com/phorum/read.php?1,853018
http://www.mgexp.com/phorum/read.php?1,2770960
http://mgaguru.com/mgtech/ignition/ig129.htm


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B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
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The bulk of failed condensers have either deteriorated internally from age (50 year shelf life under ideal conditions), or fail from inadequate grounding. I don't mean lack of ground, I mean a marginally acceptable ground. Stop reusing 50 year old ground straps and battery cables for starters. For that matter, 25 years old is probably bad - whether you can tell on the outside or not.

Then look at the daisy chain of grounds from your condenser screw (which must be very tight), to the breaker plate's top to the breaker plate's bottom to the distributor casting to the clamp to the cast iron sleeve in the block to the block, to the chassis, to the battery via all the spot welds in the car's body. This all needs to provide a clear ground signal so that the condenser can discharge 100% - 30 times per second while you are cruising at 60 mph. You may want to double check that math, but you get the idea. Its critical. The largest epidemic of condenser failures is in cars with the worst factory grounding systems - Minis and TR7/8s that run points. Its also extremely common to see failures in MGBS with other electrical gremlins, and cars that have been freshly restored where paint has creeped over many common grounding locations and insulated that ground.



jeff@advanceddistributors.com

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
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Good advice from Jeff, as always... thumbs up

For the record, if cruising at 2,400 rpm, the coil and condenser are charging/discharging 80 times per second...

Dick


In reply to # 3409029 by B-racer This all needs to provide a clear ground signal so that the condenser can discharge 100% - 30 times per second while you are cruising at 60 mph.



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(Often wrong, but always certain)

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lewisrn Avatar
lewisrn Gold Member Bob L
Danville, IN, USA   USA
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1980 MG MGB "The "B"
Yep - make sure your grounding points are good and install an electronic ignition and all will be well. devil smiley



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Boris67MGB Richard Boris
Kings Park. NY 11754, USA   USA
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1967 MG MGB
Points will wear out, even with a functioning capacitors. I check my capacitors with a capacitor checker (uses ac signal). If it reads OK, no shorts/opens, I continue to use them. Only failure in 50 + years was a fractured ground lug holding the capacitor to the base plate. BTW, I have some antique vacuum tube radio equipment from 1930's with original capacitors; operating at very high comparative voltages. I think the recent failures are from manufacturers making junk.

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ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
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1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
1995 Toyota Highlander "Hi Ace Van"
2022 MG ZS
In reply to # 3408987 by benhutcherson . I don't know offhand what the rated capacitance of our condensers is, but I'd almost be tempted to fit a tantalum or the like capacitor to the ignition coil.

IIRC it's about 0.2 uF. I doubt whether a tantalum would survive, there are several hundred volts produced across the points, when they open.

Herb



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tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
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But of course, with an electronic ignition you don't use the condenser.

Yea, crap Chinese parts. Google bad condenser.

Anyway, there are several WEB pages showing how to adapt a standard high quality cap and put it where it belongs, at the coil. I know some don't believe this, but you actually want the cap where the power is, not at the far end of the wire. How condensers ever got put inside dizzies I'll never guess.

In reply to # 3409071 by lewisrn Yep - make sure your grounding points are good and install an electronic ignition and all will be well. devil smiley



Cogito ergo sum periculoso

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rntanner Avatar
rntanner Roger N. Tanner (Disabled)
Oxnard, CA, USA   USA
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1970 MG MGB
1977 MG MGB
There is a modern version with no breaker points or condensers:

Pertronix solid-state switching which allows you use a spark coil which provides a much hotter spark:

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=38780

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=98397

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=98397

Yes, these parts are expensive. Yes, they will outlast your life of driving that MGB.

Yes, you still will need to install new spark plugs every 12,000 miles.



Roger N. Tanner
Professional Engineer, Retired

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benhutcherson Avatar
benhutcherson Ben Hutcherson
Maryville(St. Louis), IL, USA   USA
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In reply to # 3409198 by ozieagle
In reply to # 3408987 by benhutcherson . I don't know offhand what the rated capacitance of our condensers is, but I'd almost be tempted to fit a tantalum or the like capacitor to the ignition coil.

IIRC it's about 0.2 uF. I doubt whether a tantalum would survive, there are several hundred volts produced across the points, when they open.

Herb

Fair enough on tantalum. I think I remember peak voltage as being in the ballpark of 300V, so I'd want a 600V rating or better to be safe.

The stock ones I've seen cut apart are a roll of foil and use mylar for the dielectric.

There are ceramics in the .2µF range with a 630V rating, and possibly 1000V if you dig enough. That might be reinventing the wheel, but it would probably effectively be a lifetime part.

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ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
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1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
1995 Toyota Highlander "Hi Ace Van"
2022 MG ZS
Remember that the capacitor has two functions, to provide a tuned circuit with the coil, but also to quench the arcing and burning of the points. To do this it is prudent to have the capacitor as close to the points as possible, otherwise the resistance and inductance of connecting wires may reduce its effectiveness, and considering all the earth connections Jeff pointed out.

Herb



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tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
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The caps need to take high current. Tant's are not the best choice and have a much larger temp variation. If there was a ceramic that could do the job, I am sure they would be in common use as they would be cheaper. Originally they were paper/foil, then mylar/foil, and now most are metalized polyester film. Cheaper. The failure mode is that instead of sputtering the ends of the foil and attaching reliable leads, they use a mechanical contact dimpled plate and hope it makes contact. Cheap crap is the problem.

Again, the WEB has many articles on this problem. GTS.



Cogito ergo sum periculoso

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benhutcherson Avatar
benhutcherson Ben Hutcherson
Maryville(St. Louis), IL, USA   USA
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In reply to # 3409068 by dickmoritz Good advice from Jeff, as always... thumbs up

For the record, if cruising at 2,400 rpm, the coil and condenser are charging/discharging 80 times per second...

Dick


In reply to # 3409029 by B-racer This all needs to provide a clear ground signal so that the condenser can discharge 100% - 30 times per second while you are cruising at 60 mph.


2400 rpms? Who drives their car that slow? smiling smiley

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