Technical Ignition Condenser problems

I just got back from a fun racing/driving adventure. I have an altered wheelbase Chevy II, built like an old match race car from the mid 60s. Blown 427, mostly old parts on the car, with a few things modern to make it survive street driving. The ignition system is a Mallory dual point tach drive distributor, and a black can coil. It has worked reasonably well, I've put over 10k miles on it. But started acting up last fall, and has got a bit worse this spring. Turns out the condenser was acting up, and it just took me too long to figure it out and replace it, due to some strange circumstances.

Anyways, a friend who was around when I finally figured it out sent me a link to an interesting article about fixing Little British Cars.

http://www.nonlintec.com/sprite/cap_failure/

I guess I'll see if I can find that old brass Mallory condenser I think I might have somewhere around my shop.

Has anyone found a really high quality modern replacement?

 

Interested in this as well. I've had a few go bad recently. Most recently was on my Triumph cycle.....uses a car condensor. Anyhow, the wire pulled out of the thing! No preload on it or anything! I realize the Triumph shakes, but to just fall apart? I hate modern crap......

 

My twin brother David, who's an electrical engineer, was with me on the trip, so he's interested in this too. He suggested using this

http://www.mouser.com/ProductDetail/Cornell-Dubilier-CDE/940C6P22K-F/?qs=zsnhSutGCZWd1UevJM1khQ==

with a clamp to mount it, and fine stranded wires connected to the leads to keep stuff from breaking from vibration.

 

Great read. This might have been the issue I had years ago with the Rocky33. Sure sounds like the symptoms.

 

Mine would occasionally "drop out", misfire, or stumble on acceleration, but it would work fine for a long time. At the strip it would pop and miss at random.

 

A picture of mine. Kind of hard to see inside the can, but there are two black lines, where the little tabs on the plate made contact. Poor contact, it was apparently arcing there. There is a little black mark on the contact on the wire end, also. This one has a 1/4" thick rubber cap that holds in the wire, and provides a little bit of elastic compression. but the roll of actual condenser material is quite a bit smaller than the ID of the can, so it can move around.

lousy design concept. Especially for something that moves around, like an old race car.

 

Condensers or capacitors whatever you prefer are measured in microfarads(not sure if correct spelling).

The Mallory big brass are .36

You can get a modern one that is .36 or greater although they do not look correct. They are made for marine applications. Part number 580256 and 580231 if I remember correctly. Check your local OMC dealer. I can't remember which is which but one is rated for .35 and one is .37 to .45 once again going off memory.

If you like I can find a link to chart that has all the part numbers and applications. One was a replacement for a inboard OMC big block Ford.

 

I use a Vertex mag condensor that a mag friend has made for his shop. Never seen a bad one ! They are .36 and some put them inside the old mallory brass case etc...
The cost $32 but they have been worth it.....

 

good info, and makes sense. i have had a few appear to go bad when they get warm, so the can must expand and lose connection.
i wonder if, in a pinch, the condenser could be squeezed, to get going again?
question about condensers, if i may? i have an off topic 72 mercedes sl. it uses a set of points and originally a condenser. i went to tune it up and the condenser wire was cut off. when i went to order another one they told me they are not needed. it runs good but.........

 

I also was wondering it a little pinching of the condenser housing would help..If there is no mounting bracket in the way a turn or two with a dull pipe cutter to swage a couple bands in the OD to keep insides from moving around? And or maybe a C clamp that has a "C" shaped foot to straddle the wire at the wire end and a little pushing on the end of the can with the clamping screw to compress some for internal contact tightening....How much either direction of making the can smaller will help till it hinders?

 

I think there are several different internal designs, and when they go bad, the common thing is that there's some arcing going on at one end or the other or both. Crimping it shorter, even just a little bit, would probably help. It looks like there's quite a bit of tolerance for how much you crimp it, it won't get messed up unless you go more than, say, 1/8" or so

 

The Mercedes has a capacitive discharge ignition and doesnt need a condensor......

 

wonder if one from a aircraft mag would work? they don't use junk parts. aircraft spruce lists some.

 

Failure of the condenser is a common thing in the Model A world, caused by excessive heat, and/or poor quality. There is a company called A&L that makes a "burnout proof" condenser that everybody swears by. I am not sure if it would have the correct uF rating for the Chevy points, but it might be worth looking into. I remember years ago you would see a lot of stuff in the books about the points building up on one side or the other if the rating was wrong, and they suggested it was common to use different ones at tune-up time, but I never did this, I just told the man at Napa to give me the best Echlin stuff he had, whatever the book called for. I am not sure this is still valid today, but I still use it in all my old stuff. Good Luck!

 

I have a Dual point Tack drive GM Distributor in my Merc
and when I had Problems with the cond. I when to Napa &
got a new one, my Cond mounts on the Coil.

Just my 3.5 cents or
when the Cows
come Home!

 

Whats the PN# ?

 

Imagine that, a "capacitive" discharge ignition doesn't need a "capacitor". Go figure.

 

ok........but i wish i knew what a capacitive discharge ignition was.

 

the capacitors are in the amplifier....the points have very little load on them, so they don't have pitting issues.

 

here's the schematic for one...does that help?

 

Echlin was making a pretty good replacement condenser. I am not sure where they make their parts any more, but they were still making good parts last I checked.

I may have an old Mallory trash can here if you don't find yours.

 

i have a bunch,[hundreds] of nos ignition parts, including condensers. made before the 70's. are these made the same way? or should i cut one apart and find out.

 

Kind of, but it doesn't show any points.

C2 and C6 are capacitors at the discharge to the distributor. So this system charges caps in between firing cylinders. Hence the term "capacitive discharge" (in this application the caps serve like miniature rechargeable batteries that store very high voltage, charge almost instantly, and have almost indefinite charge/discharge cycles). Cool.

 

I replaced the Loadmatic distributor in my 1956 ford with a rebuilt 57-62. The condenser started failing in 3 months. Replaced it, lasted 4 months. Removed points and condenser and installed a Pertronics II and never had a problem. It took me 2 yrs to find an additional Mallory condenser for my dual point dist in my GMC. I'm glad to have it...

 

So, I read the linked article, but I'm wondering if we're all missing something here. The blame is being laid on poorly constructed condensers, and that may very well be a problem. But I think failed condensers can also be a symptom of other problems. What I mean is, think about why condensers, which are placed in the primary circuit of the ignition coil, need to be rated so far higher than 12 volts (the article calls for 600 vdc rating). They only see 12 volts while the starter is engaged, after which the voltage even drops lower, right? Or is it? Take a look at this diagram of an ignition system, and look where the condenser is in the circuit.



It is exposed to the primary side of the coil, right? The coil is a transformer, it transforms low voltage to high voltage. It does that by inducing a voltage in the secondary windings when the field collapses on the primary side. Well, it will also go the other way. Normally the high voltage is created in the secondary side of the coil and discharges out to the spark plugs. But what happens when the discharge is interrupted, say by a faulty spark plug wire or even a failing spark plug, maybe the gap it too large and the spark cannot cross it.

So I'm just thinking about my experience and knowledge of tube guitar amplifiers. I do a lot of repair and service on these, even design and build my own (yeah, tubes are still the way to go on electric guitar amps). These amplifiers also use an output transformer that functions the same way as an ignition coil, but in this case it goes the other way around, transforming a high voltage to a low voltage. But these amps always, repeat ALWAYS, require a load connected whenever they are amplifying a signal. There has to be somewhere for the amplified and transformed signal to go, either a speaker or a power resistor, or something. They have to be able to release the voltage that is generated in the secondary side of the transformer. Without a load attached for the secondary side of the transformer to discharge, the voltage will build in the secondary coil until a point that the magnetic field collapses, which induces a voltage into the primary side of the transformer known as flyback voltage. This flyback voltage can be several times higher than the normal voltage applied to the primary circuit in normal operation, and can result in disastrous arcing at the power tube sockets, or it can even pierce the insulation on the transformer winding and destroy the transformer. Well, I say that's similar to what happens on the ignition system when a spark fails to occur. And the flyback voltage can be high enough depending on conditions, to cause arcing in the condenser housing. And once arcing occurs, it lays down a carbon trace (the black marks you see) and those carbon traces are conductive (when arcing occurs at the tube sockets of an amp, it typically requires the sockets to be replaced, because you can't clean the carbon trace off, and it will induce further arcing), which leads to more arcing, and eventually a failed condenser. Which you might blame on the condenser, so you replace it and everything works fine until it happens again, and the new condenser fails, and you start blaming the poorly constructed condenser as the problem. Maybe the real problem is somewhere else. If this happens once on an engine, maybe it was just a cheap condenser that failed. If it happens repeatedly, I'd look beyond that.

 

Electrically, anything will work, rolled up Juicy Fruit gum wrappers and a paper clip, etc. But it has to be the correct MFD or uF (capacitance) and, be of sufficient voltage rating not to break down.

A 600 volt 0.22 uF film capacitor should work fine, if that's the value of the OEM. Note how large they are compared with the junk sold from you know where. It's difficult to make a small, high voltage capacitor. There isn't much call for them anymore in modern electronics.

The condenser in this application (what little I understand) is placed in parallel across the points, to prevent arcing of the points as they open, and this also makes the spark at the plugs much greater.

One of the things mechanics used to look on a tuneup was whether deposits would build up, on the stationary or moving contact point. Ideally they would be the same. In those instances I've read the consensus was don't change the condenser out. The production tolerance of actual capacitance value varied somewhat. There was a routine to either shorten or lengthen the wiring (to change the capacitance slightly) and keep deposits from building. A good, quality condenser should last a long time and routine replacement not necessary for any reason I can think of.

Capacitors (used to be) of this type used to be made of paper and foil. The modern film capacitor (though not designed for auto use) should work fine and last far longer. It won't look right or fit in the distributor. Somebody could probably make a nice little cottage industry selling high quality condensers in vintage package.

 

Does anybody remember the condenser wire length rule? If one side of the points is getting buildup, you shorten the condenser wire til you stop getting build-up and pitting on the other side. Something like that.

 

Before solid state car radios came along, they used a "buffer capacitor" in the power supply. These were always rated at 1600 volts DC. I'm sure they never saw anywhere near that, but they had to use that voltage rating to get them to stand up. Modern materials (poly film) hold up far better than paper.

 

This may help..or not..up to the point of explaining how the capacitor functions anyways....

 

Just for fun, put a scope on the primary side of a point ignition system. You'll see a rather high voltage, it has to do with the field in the coil collapsing. the condenser has to be "tuned" to the inductance of the coil primary side, to be able to minimize arcing of the points as they close. The "step" near the middle of the trace is 12v, so you get an idea of how high of voltage the ringing spike is. (yes, this Tek 535 scope is as old as my car)