Technical Points ignition/condenser question

See like I said not real. He survived at least 6 times...

 

Pay's to have a condenser in your back pocket.

 

Who gives a shit so long as we all know how gap the points...

 

Huh. Never thought about it. That's really something!

 

While I have the ear of you electrical guys: I heard a long time ago that a fouled plug could be made to fire by loosening the boot, creating an extra gap. I think I even tried it and seemed to work. True, and if so, why?

 

it's the same reason they use resistors in spark plugs and in plug wires. It lets the voltage build up higher, before it sparks. When the plug fouls, the deposits conduct electricity, and bleed off voltage, so it doesn't build up to the necessary level that it takes to jump the gap on the plug.

A very lousy explanation, sorry...but that's the basic idea.

 

"If the mound is on the positive point (moveable contact?), install a condenser of greater capacity; if the mound is on the negative point (stationary contact?), install a condenser of lesser capacity".

So, am I looking at this the right way, assuming negative ground?

 

You should get a scope, I bet you'd find it really interesting. I bought one because I couldn't figure what the &@$k was wrong with my engine, and throwing new parts at it didn't help, in fact it actually got worse as I went along. The reason a completely fouled plug can be made to fire by pulling the boot back, the extreme air gap raises the coil firing voltage by quite a lot, and will blast through the fouling to get it going again.

Bubba does a pretty good job explaining stuff in past posts here, but basically an ignition only supplies enough juice to fire the spark plug across the gap, and no more. The spark plug (and rotor/terminal) gap plays a big role in the firing voltage. A "stock" contact points ignition coil was rated around 20,000 volts (potential), but ordinarily, only about half of that was required at idle and a little more under load and compression. The rest is "reserve" voltage. Lean fuel mixtures, worn plug electrodes require a higher firing or "strike" voltage to get the spark started.

Anyway, the coil "firing voltage" is a specific line on the display raster of an ignition scope display screen. It's an important diagnostic, it tells you at what coil voltage each cylinder is firing at in real time and if there is any defect overall, or maybe a defect in a plug wire, or plug itself specific to a cylinder.

Each cylinder firing line should be about the same height (voltage) and overall the line shouldn't be spiking, maybe only 8 to 10k volts. Idle doesn't place much demand on the ignition system. But increasing loads do. One of the old school ignition "torture tests" was to put the car in high gear and try to creep along about 5 or 10 miles an hour. Engine shouldn't buck or misfire (ignition wigging out or arc to ground)

It's really tempting to install a "45,000 volt Plasma Arc Generator" ignition coil, but that isn't really how it works, for one thing if the other components aren't up to snuff or they aren't matched properly it will just bleed off somewhere other than the spark plugs, arc to ground, maybe crossfire through induction, burn up the rotor, inside carbon tracking, stuff like that.

 

"TRUCK64" is correct. About 25 years ago I built a flathead with one of them "Plasma Arc Generator" ignitions. Actually, it was a top end MSD distributor, box and coil. That damned thing kept eating the coil tower in the distributor cap with too much voltage. If a cap lasted 2000 miles, I was lucky. MSD caps were expensive at first, but after I found out you could use a standard GM cap, I switched to them and saved some dough. Some guy who had to have the car (it was a '36 3-window) talked me into selling it before I had to fix it properly.

As I have said before, this is one case where my signature line is inappropriate.

 

I think so....

 

Yes used to do that with my 65' I6 Comet when it needed valve seals.

 

Some of the old school guys would leave the condenser alone during a Tune-Up if the points were otherwise wearing evenly. Replace the points if worn, leave the condenser alone. This makes sense, because even then condensers were a bit of a crapshoot, if only hecause the +/- capacitance tolerances weren't as tight as they are today. There were things that could be done, like tying the condenser lead in a knot, this changes the capacitance slightly, enough to matter, for long term points health. But leaving the old condenser installed might have been a problem if the customer was wondering why he or she didn't get a brand new condenser for the $6.95 Spring Special.

Wire lead length affects stray capacitance in a big way. This is especially important at radio frequencies. If you look at the very first radios ever built, they were physically built just like the schematic might look on paper, nice neat long wiring bundles and buss wire laid out straight like rows of plumbing pipe with parallel runs and tidy 90 degree bends. Oops!

Turns out this doesn't work at all for radio, they would become unstable and start howling and squeeling and couldn't operate at all with the ever higher and frequencies. That's how the "rats nest" wiring bundles under the chassis for most electronics was born, it sort of looks bad, but the shortest direct lead length possible is always desirable for stability.

 

Again, close is good enough in hand grenades, horseshoes, and condensers.

 

Truck64, you have caused me to think about stuff that I haven’t used since tech school. As soon as I started reading your post, it all came flooding back. Thanks for the refresher. At work I don’t use a lot of ignition diagnostics, I work on Diesel engines. The thing that really amazes me, is the current thought that “how did cars run without electronics”. People forget, more likely never knew, about how things “worked back then”. Every once in a while, I’ll hear at work “I wish cars/trucks were as simple as they used to be”, this causes me to reply, “don’t kid yourself, the simple stuff(as you say) used to kick mechanics asses back then too.

 

I believe it causes the ignition to develop more voltage to jump the gap...

 

that's an eloquent way to put it....

 

Right - everybody "knows" this but the real question then, is why can't the spark plug gap just be opened up to say .090" and get a really hot spark?

The answer of course is there are limits to how high the initial firing voltage in a coil can get before there is damage to components or misfire at high RPM caused by things like arcing to ground or crossfire.

 

As a teacher, I have to have update and technical training each year.
Between reading through this one and the thread about brakes not locking up, I feel that I have met that requirement.
I need a moderator to print off a certificate.
Thanks

 

I thought it had more to do with the voltage required to make a spark jump a specific gap, increases with air density. But I could be wrong.

 

ok so heres what i did to nip the condenser think in the butt forever ..
i have a vintage mallory im getting ready to install ,and i got to get my eggs in a row , the big brass can condensors (capicator) are pretty pricey like 40-60 bux and more , so i went on ebay and found this
https://www.ebay.com/itm/255077704751?hash=item3b63d0e42f:g:k-kAAOSwKcJhCmFT 20 bux shipped (i have no connections to ebay or the seller.. bla .bla) its a capicator tester no more guesswork EVER,, now thats all this does ,, makes a noise if bad and gives you a Uf (micro farrads) reading if its good ,, i put it on the 200 range ,, mine came in at 38 was in range for dual points and i read should be 24ish for single ( dont kill me on my numbers theres smarter guys on here than me ) but i spent 20 my stuff is good and im happy , no guess work or voo doo diagnosing ,, we allways replaced them with the points growing up with no way to test ,, were they bad ,, or were we replacing so they could sell tune up parts ? oh boy ,,,,,,,lol buy a tester
fabricator john
miss you dad

 

Well you're probably right on the cause, I'm not smart enough to know the why, just dumb enough to observe the effect aka "that don't work!".

 

Those modern capacitor checkers won't work for you, not the way you think. Sorry to be the bearer of bad news. They will tell you a little bit, but they are designed mostly for modern low voltage capacitors. Not the stuff used here.

Even a simple ohmeter will tell you if an ignition capacitor "should" work, in other words weed out the real duds, if it fails that test, it is definitely bad, but if it charges up OK it just tells you that it might work. Maybe.

As far as measuring the actual capacity, I've never found that necessary, particularly useful, or ever found one out of spec. They can test fine at .22uF and be completely defective in use. A key test for these old capacitors is DC leakage, or what I think in automotive parlance is called insulation resistance. About 500 volts DC is applied, or up to the working voltage of the capacitor (condenser). That $20 special "capacitor checker" can't do that, and they don't need to, because high voltage capacitors are mostly a thing of the past, or getting there anyway.

I use an Eico 950B for capacitor testing purposes, it has the cool green "Magic Eye" tube for indication. (It will also zap the shit out of you if not careful, UL standards for grounding safety were a bit different back in the day.) The pictured unit is not mine.

Basically, you can charge up a good or serviceable ignition capacitor (condenser) with 500 volts and it will hold it for a long time. If you want reliable ignition and best possible spark in points ignition, the condenser has to be serviceable. If you get a good one, don't $&@k with it, it should last a long time, but there are no guarantees.

 

I’m not an electrical expert but my father was he taught me that it takes a hotter spark as you increase compression in a engine just because you have spark with the plug outside the engine doesn’t mean you have spark with the plug in the engine under compression
Also you go by color and size of spark
“A nice fat blue spark “ he would say
And the length of gap it would jump 1/4 to 1/2”

 

I think I’ve seen somewhere that aircraft magnetos were sometimes pressurized for high altitudes to keep random electrical paths from developing in ‘thin’ air.

 

I should find one of those...just for fun....

An interesting thing about ignition condenser failure--it seems to be a problem with the basic packaging design, in some cases. I had a problem several years ago with one on my Chevy II, and eventually found the cause of the problem. It was the design of the thing. What holds the contact in place is the elastic tension of the rubber plug in the end of the can. Since the parts eventually compress inside, the tension goes away, and the connection gets loose.

I solved it by using an electronics type capacitor, with two wire leads, and haven't had any trouble since. I did some research at the time, and found that the guys with British cars were really having a lot of trouble finding a good condenser, and they'd taken some apart and found similar problems.

https://www.jalopyjournal.com/forum/threads/ignition-condenser-problems.1014719/

I don't know if the capacitor tester would find this problem. It might.

 

Hmm, nothing about me is eloquent...

 

That was a fun read to go back through. Thanks for posting.

 

Defective capacitors have almost a cult following, though definitely not in this hobby. Vintage guitars, and vintage guitar amplifiers. The old way to manufacture them was simply foil and kraft paper as dielectric rolled up in a tube and soaked in oil, dipped in beeswax, or maybe plastic. They didn't last too long in service or weren't expected to be in service very long. If you've a vintage Fender or Strat and stuff like that, the hipsters want to see those original, leaky capacitors. It's part of the wooly "tone" and mojo the vintage stuff has.

The capacitor checker is more of a "how bad are they" kind of thing for vintage gear. In some circuits, like a tone control, a bit of "leakage" won't hurt anything. But defective high voltage blocking and coupling capacitors connected to output transformers, output tubes or transistors and all that stuff, will start roasting stuff.

Exactly none of the passle of good used old school ignition condensers I've laying around pass the test on the Eico. I think they might "work" pretty good but that might be deceptive. Condensers (and coils) are also supposed to be tested at normal (HOT) operating temperature too. I didn't try that.

I decided a Sprague poly 600 volt 0.22 should do the trick for ignition duty, it is very clean ignition pattern on the scope. Maybe it wouldn't hold up under extended use, though the spec sheet seems to show that it should.

 

^^^^^ If one blows "Don't Worry" much over it.