burnt ignition points

[Anonymous-0]

i am working on a cockshott 20 that has been converted to 12 volts about 20 years ago and has been running fine since then. the lady called and said it would not start , so i went over and found no spark , so i put in a new set and it fire right up , but did not run well for about 5 minutes and stopped. i checked for spark , found none so i pulled the cap and found the new points completely burnt . i am going to put in a new condensor but i am inclined to think that the problem is elsewhere as i have never seen points burn that fast. it will be a few days before i get back to it but i am leaning towards the charging system gone crazy . it currently has a coil with the internal resistor. any ideas sam

 

[old]

Well other then being in the wrong forum. Any how could be a bad coil or a bad condenser. Only way it could be the charging system would be that some how the battery was not staying hooked up since no matter how much charge the system is putting out the battery will only let so many volts to pass through it

 

[Anonymous-0]

Coil could also be hooked up wrong. Negative ground, the points get fire from the negative terminal of the coil. Positive ground, the points get fire from the positive side of the coil. If they are hooked up wrong, burns up points fast. Could also be a bad coil.

 

[Fern{Mi}]

If you had put in a new condenser, replace the points and reinstall the old condenser.
I learned dad's rule and it has worked fine for me for years.
As long as the points wear out evenly keep use the condenser. Replace condenser if points unevenly wear or burn out.
Oil will destroy points, even the oil in your skin. So keep your fingers clear the mating surfaces. Gap the points with a new match book. Even feeler gauges are contaminated.
My $.02 worth.
Fernan

 

[Gene]

Check the voltage across the point gap, engine not running. You are wanting to see 6 volts to upper limit of 9 volts.

Also check the voltage at the coil to distributor wire terminal with the engine running and alternator charging.

One of two problems. Its either a bad condensor or voltage to high.

 

[John T]

Actually,

1) The voltage "across the points gap" as you mention would be near 0 when they are closed and if not they are burned or carboned or not closing fully.

2) When the points are open, the voltage "across the points gap" (which is basically the voltage between the coils output to frame ground) would be 12 volts if its a 12 volt battery. Theres no voltage drop across the coil or any ballast resistor etc if theres no current flow you see... The points have to be closed so the coil conducts current and when closed theres zero voltage drop across a basically short circuit (the CLOSED points unless burned or carboned up)

3) I believe the indicated he had an internally ballasted coil i.e. theres no external series voltage dropping (12 to 6) Ballast Resistor. If he had a ballast (where using a 6 volt coil on a 12 volt system) and ifffffffffff the points were closed and good, thats the situation where there should be around 6 to 7 volts on the coils input (NOT to distributor) terminal since theres an IR drop of 6 volts across the ballast.

Hope this helps

John T

 

[John T]

Common causes of premature burning of the poinst are:

1) Bad/open or weak condensor, or its not wired in as it needs to be or its not well grounded.

2) Excess coil and points current caused by lack of an external series voltage dropping (12 to 6) ballast in cases where its a 6 volt coil on a 12 volt system,,,,,,, or perhaps a bad coil in cases where its a 12 volt (internally ballasted) coil.

3) I dont see the charging system (its regulation) being so bad it can raise the battery voltage so high as to cause points burning as fast as you indicate. It takes a lot of current and energy to raise the voltage on a 12 volt battery to 14.5 like a high amp alternator can while an original generator system has even less output

4) If the distributor shaft has wobble from bad bushings/bearings that can mess up a set of points.

Id be checking the condensor (and its wiring and ground) and the coil to be sure its a 12 volt rated unit and NOT a 6 volt coil which unballasted will burn points faster.

John T

 

[old]

That being hooked up backwards and causing problems is an old Wives tail and a coil hookup up + ground or - ground will not burn them faster either way since all that does is makes them jump one way out the other. Just like if you ground a light bulb on a tractor it does not care which way the power flows

 

[John T]

I "pretty much" agree with you Rich (as usual) Id say wiring a coil at reverse polarity causes at least "some" problems though because the coil operates at less efficiency n may run just a tad warmer (works harder) and fer sure theres less spark energy avaialbe for discharge across the plugs gap buttttttttttt like you I dont see that much appreciable change in the current flow through the points and coils primary (Regardles if correct or reverse polarity) so as to cause the points to burn up very much (if any) faster.

Keep warm down on that Missouri farm now....

John T

 

[old]

Ya spark does not care which way it goes but ya if it does go back wards it might be a tad weaker but then not weak enough to cause much of any problems unless it is a weak spark in the first place then that could add to the problem

 

[John T]

Fun discussion Rich, for us at least but we may bore others lol. Its easier to arc current (requires less voltage) from a relatively hotter surface (plugs electrode) to a relatively cooler surface (plugs ground strap) and thats why n how the coil is more efficient (less work maybe cooler with less heat losses) when wired at the correct polarity. Its the same reason/theory in the old vacuum tubes where there was a heater under the cathode and electrons were emitted off it up to the cooler unheated plate.

Coils work BEST at the correct polarity (per the above) althoug the primary current and points current dont see much change

John T North of ya in Indiana

 

[old]

Ok John here is one for you. If you could insulate the housing of a condenser and then hook it up so the wire went to ground and the case went to the hot side will it still work as well as it would if hooked up the correct way?

 

[John T]

YEP, it (A NON electrolytic capacitor) will still work the same. All it has is like two rolls of conductive metallic foil with a paper insulator in between, then shes all rolled up with one plate attached to the metal conductive case n the other to the external lead. A capacitor is just two conductive plates close to each other with insulation between them so opposite charges buid up on the opposing plates. Hook it to DC and it will initially conduct just a bit until equal but opposite charges build up on the opposing plates, at which time it no longer conducts DC current. It will conduct AC and its impedance is frequency sensitive Xc = j omega C

Youre an old Navy sparky arent you??

Take care Rich

John T

 

[Anonymous-0]

You can call it an old wives tale, if you like, Old. Think of it this way, why do they make the one point contact with a hole through the center of it? Because, as the spark jumps from one point contact, to the other, it takes a little metal with it. If you hook it up backwards, it defeats the purpose of putting that hole in the points, thereby eating up the points quicker. Don't want to really debate it for hours, but for longest life, hook the wires up right.

 

[old]

Well see most point sets I get do not have a hole in them and as John T says very little difference in amp draw and amps is what causes them to burn. Ya either way it is better the have the coil hooked up correct but not having it does not burn up the points. Ex navy E.T. here so I do understand things like this

 

[old]

Yep was an E-T in the navy but was not sure if the condenser/capacitor where the electrolytic type or not. I have forgotten so much of what I did know way back when that some times I ask things just to refresh what I do know I know if that make since. Ya at one time I understood and gates or gate nan gate and nor gates plus could count in binary and octal and even did a little programming

 

[jsulen]

Thanks for sharing the Common causes of premature burning of the ignition points..
ignition points