[dpoltzer]

My 1970T/A with a bone stock motor seems to be burning up ignition condensers! Car runs flawless for several months and then motor starts to run rough and stumbles. I replaced the condenser with a NAPA condenser and it runs great again for a few months and the same condition happens again. I am on my 3rd condenser in about a year and have under 500 miles on the car. Could a bad ignition coil be causing my issue or what else can I check as this is getting old. I did just order a new Accel point set with a condenser that will arrive in a few days but I hate to replace these components ($40) just to have them go bad in a month or so. Any Ideas on what to check? (car is 100% stock and original so I am not interested in HEI or adding pertronix) Thanks.

[Tom Vaught]

Have you looked at your distributor cap to see if maybe the terminals are in bad shape, (or the Rotor), and requiring the condenser to work harder to have the ignition system work properly. Coil could do the same thing.

Tom V.

[Dragncar]

Not sure if they are available anymore, but I have had a all brass MALLORY condenser for over 30 years.
Condensers either work or they do not. No in-between from what I understand.
If you could find out a way to hide a CD ignition (MSD) that would be a option.. They do not need a condenser to work.
Tom is right. change you cap and rotor. Try a different coil and see how it does. Go from there.

[steve25]

There most likely failing from a over voltage condition.
What amount of D.C. Voltage do you read with digital meter at your battery terminals with the engine running at 3000 rpm?

[Gary H]

Originally Posted by steve25

There most likely failing from a over voltage condition.
What amount of D.C. Voltage do you read with digital meter at your battery terminals with the engine running at 3000 rpm?

X2! Sounds like a overvoltage issue. I had this happen on a bone stock 61' Catalina I own. Come to find out someone previously had replace the resister wire to the coil with a standard wire and it was getting too much voltage to the coil, points, and condenser, causing them to fail.

["QUICK-SILVER"]

(1) Ohm test the resistance wire.

(2) Ohm test the coils primary resistance.

Points and condensers don't hold up with less than 3 ohms total resistance between the two.

Clay

[Tom Vaught]

I have seen a few cases where the "Hot Set-up" for racing was to give full voltage to the coil/points/condenser, (which caused damage to those parts as well as to the rotor and the cap/wires.

Tom V.

[johnta1]

If the condenser is actually bad, the grounding is probably bad.

When you replaced it, did you do anything else?
Change the bracket holding the condenser?
Reset points?

The outer housing of the condenser needs to have a good connection to the bracket holding it. The points plate has to have a good connection to the distributor housing. The housing has to have a good connection to the engine block. The engine block has to have a good connection to battery ground.

Any one of these can cause a problem.

[george kujanski]

The voltage stress on the condenser (capacitor) is when the points open. The voltage then jumps up to a few hundred volts (primary coil voltage) which is then multiplied in the secondary windings of the coil to tens of thousands of volts to fire the plugs. The DC voltage on the capacitor after the plug fires (approx battery voltage) is minor compared to the primary spike.

I find it unusual that your system eats thru capacitors, usually they are robust devices, unless the current versions of them are junk.

Is it possible your coil is wired backwards? (-) side of the coil should go to the distributor points, (+) side to the ignition (key) wiring.

george

[Formulabruce]

If you think the quality of the Condenser is suspect, go back to NAPA and order a Condenser for a Boat. A 1988 cigarette with a chevy 350 is an example. Napa has some Echlin MARINE line that are typically of better quality. (There is also Blue Point , or whoever bought them) .While the chevy points may be different, the Condenser is the same. Due to reliability on the water, or in the air, these products are built to a higher standard.
This goes for AC Spark plugs too, if you can't find what you want put a "M" in front of the number and ask for it. Example "MR44TS"

[mgarblik]

Good list of things to check above. I will add a couple more. Key on, run position, you should not see over 10 volts to the coil. More like 9-9.5 would be typical. Second: There is a little black ground wire that grounds the breaker plate to the distributor body. It is very common for that wire to break or just pull out after 50 years of use. Check that as well.

["QUICK-SILVER"]

Does this distributor still have factory lead wire from points to coil (-)?

If so, check where it passes through the distributor body. You move it when you change condensors and it may be cracked up or frayed and grounding out.

Clay

[Sun Tuned]

Post #8 and #11 for sure.

Sometimes these condensers are close. Haven’t seen any lately that we’re too far off. None are as close as they used to be but they may be more consistent now than they used to be. Not sure if they’re constructed with more machinery than they used to be either. Not really my department on that.

I will say that a feature of most better quality volt ohm meters are a capacitance meter or function. I’ve seen people take these and check condensers and think they are in spec.

This is not the whole story though. That’s just a general test to see the value of it laying on the counter. The blood and guts part that you would be interested in is a loaded test.
Where you load the condenser and see what it’s leakage and/or capacity is. That’s what you really want to know.

Most of the better quality tune up testers and the deluxe versions of the distributor testers allowed this.

George may have some equipment in the lab that could do same.

[dpoltzer]

I will check thru all of these excellent points each of you has made this weekend when I have some time. Thanks again and I will report back. Dave

[george kujanski]

The book specs show the capacitor as .18 to .23 uF. (microFarads). This equates to a value of +/- 12% which, in the electronics biz is pretty wide. These parts, In an ignition system, mated with a mass-produced coil which has it's own tolerance, is basically a good design target at a reasonable production cost. A design compromise.

BTW, the main function of the capacitor is to try an keep the points from arcing excessively when they open. It also has an effect that larger values of capacitance tends to REDUCE the generated primary voltage/ secondary voltage. Lower values of capacitance increase the primary voltage/secondary voltage at the expense of point arcing. Everything is a compromise. Newer systems that use transistors for switching the coil (HEI, Pertronix, MSD, others) don't have the arcing issue, which is an improvement.

The system has worked sufficiently well for ages, and for mass-produced cars, it was "good enuf".

The book also states that the capacitor should not be changed along with the points if there is little to no metal transfer from one side of the points to the other, indicating it's a good match with the coil.

George

[Ram Air IV Jack]

Originally Posted by george kujanski

The book specs show the capacitor as .18 to .23 uF. (microFarads). This equates to a value of +/- 12% which, in the electronics biz is pretty wide. These parts, In an ignition system, mated with a mass-produced coil which has it's own tolerance, is basically a good design target at a reasonable production cost. A design compromise.

BTW, the main function of the capacitor is to try an keep the points from arcing excessively when they open. It also has an effect that larger values of capacitance tends to REDUCE the generated primary voltage/ secondary voltage. Lower values of capacitance increase the primary voltage/secondary voltage at the expense of point arcing. Everything is a compromise. Newer systems that use transistors for switching the coil (HEI, Pertronix, MSD, others) don't have the arcing issue, which is an improvement.

The system has worked sufficiently well for ages, and for mass-produced cars, it was "good enuf".

The book also states that the capacitor should not be changed along with the points if there is little to no metal transfer from one side of the points to the other, indicating it's a good match with the coil.

George

Excellent!! Back in auto mechanics school when these devices were common, the instructor told us the condenser rarely failed. We could check to see if it was shorted but that was about it. Instructor also commented that there was always a possibility that a new condenser could fail at the start if the pig tail had been pulled on too much during manufacturing. This would cause it to disconnect from the inside making it useless. So the instructor said leave the condenser alone unless you have evidence it has failed. However, when doing complete tune-ups in those days, we liked to make money and replacing condensers added to the bill.

[Ben M.]

Originally Posted by Sun Tuned

George may have some equipment in the lab that could do same.

Oh no doubt he does. LCR meters/bridges and active testers are stupid expensive even used. These are the kinds of tools I like having but very few do or know how to use them, hence all the parts changers. I may have snuck an old condenser into work once to check it and found it had an intermediate short to the case, but that was the only bad one I’ve ever seen and it was an original 45 year old Delco part so I cut it some slack.

12% tolerance on the capacitor isn’t bad, most production ones are 20%, 10% is good and anything better is usually pricey. My main concern would be the voltage limit on them, I can easily see a cost reduced version being made because it’s cheaper that is way more susceptible to voltage spikes from grounding problems. Over-voltage conditions kill capacitors quickly, much faster than over-current.

[389]

Keep the stock points distributor and use it to trigger this Capacitive Discharge box.. One of the simplest and best ignitions going.. The CD does most of the work and they recommend you remove the Condenser..

You have to pick a color, either Black or Red...

On my 427, I'm removing my HEI this winter and installing a 1962 iron distributor with the cable take off for the tach..

I had one of those ignitions on my old 462, I used an aluminum distributor back when PY was selling brand new NOS distributors. I used the MSD6AL with it. Never any issue.. The engine ran perfectly..

Today the MSD is a thing of the past. I'm going to use the Vertex Z-6 box. Says it's 100% American made..

https://www.summitracing.com/search/...ignition-boxes

[steve25]

Here’s a early Smoky Yunic cure for failing condensers and points, lol!

Just kidding , this was for better coil saturation.

[dpoltzer]

Careful inspection once distributor cap was removed easily shows the problem! Looks like the wire that passes thru the distributor body going to "-" side of coil was badly frayed. I believe wire stood up a bit too high and was rubbed thru by bottom edge of rotor. Replaced the wire and left points and condenser alone and the RA3 runs awesome again!! Thanks again everyone. ( I have trashed the idiot wannabe "mechanic" that replaced the previous condenser for not being more observant! (I wonder who that could be?)