Why do points fail?, and how to prevent it? Options

[dion9146]

I posted this story on another thread earlier, but I wanted to ask the broader question - why do points fail and how does one prevent that failure?

I have a 2.0 6 cylinder with MSD ignition, MSD Blaster2 coil and stock points. She has been running great since my engine rebuild, but over the weekend I had a problem. Driving along ripping corners in the country on a nice pre-fall day, and all of a sudden she starts running rough. So, I pointed it toward home and put the pedal down. About a mile out, she gave up and died.

After I got my Father to flat tow me home, I started on the MSD diagnostic procedure. I check everything including replacing the coil, and nothing works. I get to the point where MSD recommends pulling the system out and sending it to them for further analysis....that's when I decided to check the points. A couple of passes with the emory cloth, and she cranked right up.

The points are about 5 years old. They have 3 track events, two autocrosses and about 1000 road miles on them, both pre and post rebuild with about 3 years of sitting idle.

So, does my current system contribute to a shorter life span? Hard driving? Sitting for any period of time? Condensor bad?

I just don't want to get in the habit of replacing points every year just because. Any preventive maintenance I can do will be good.

Dion

[jsteele22]

Just to add some physics geek ramblings to what's already been said....

The coil (a transformer) is used to change from low volts/high current to high volts/low current. The job of the points is to turn that high current on/off. But problems occur in that hazy region between on and off, i.e., you have a resistance that's not zero, not infinity. In your case, my guess is that the bare metal sat for years and got a little bit of rust/crud on it. If you run lots of current through a resistor (the rust/crud) you basicaly have a tiny toaster oven. Short pulses of extreme localized heat, which (I'm guessing) can actually increase the pitting.

Another issue is what happens in the transformer. You dump a lot of energy into it, and that that energy has to go somewhere. Usually it comes out in the form of current arcing across the spark plug gap. The spark itself is electrical energy turning into heat. But if the plug wires are disconnected, the spark doesn't happen, and all that energy is still stored (in the form of a magnetic field) inside the coil. When the points start to open, the current "wants" to keep flowing (due to the inductance of the coil), and as a result a huge voltage builds up across the primary. So, even though the points are only supposed to see 12 V, as they open up the voltage is getting much, much higher. If not dealt with in some way, an arc will form, and this is gonna cause some damage. How to prevent this ? Well, the trick is to add a capacitor (aka "condenser"). The capacitor allows current to flow through it for a short amount of time, which prevents the dangerous build-up of high voltage across the points. So a bad or disconnected condenser is gonna show up as points getting toasted.

I'd have to agree that swtching to some kind of optical system is the way to go, unless you're trying to keep it strictly original. No friction, no arcing, no rust.