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Distributor cap center pin melted

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AUSMHLY

AUSMHLY

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I installed the HD8 carburetors on my BJ8 today.

I turned the key to let the fuel bowls fill. After the fuel pump stopped clicking, I turned the key fully to start the car. I let the engine turn over several times. Then tried again. Would not start. I assume it's getting gas, so I figured, no spark.

I found the center pin on the Pertronix distributor cap was melted. The rotor seems burnt on top and has some white residue on the sides.

I'm running a Pertronix ignitor. I checked the Pertronix carbon spark plug wires with an ohm meter and they seem fine. I tested the Lucas Sports Coil with an ohm meter, it's reading 3.1 ohms.

I'm wonder if I left the key in the on position too long, filling the fuel bowls. I've heard with the Pertronix ignitor it's not good to leave the key on without the engine running. Is this an example of what happens?

I have a replacement cap and rotor now installed, but hesitant to start the car, duplicating the problem.

What should I check, and how?

What caused this problem?

Thank you.

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Last edited:
Just a guess TH:

The rotor may have broken down via the rivit to GND


OH!

I think you will be ok with the replaced Items, however please locate a rotor without a center rivet. OK
 
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I think that center pin is graphite, and super fragile. But how hot does it need to get before it starts to "melt"? Many, many thousands of degrees (like 6000F). So it may be the plastic around the center pin that melted for some reason. Have you tried dissecting the cap? it might reveal the pin stuck in the melted plastic.

Now, what caused the plastic to melt? A short? An arc? Check the coil HT lead for any resistance. Check for proper grounded distributor. Did you smell or see smoke with the ignition "on"? Good luck, Gonzo
 
Keoke said:
Just a guess TH:
The rotor may have broken down via the rivit to GND
OH!
I think you will be ok with the replaced Items, however please locate a rotor without a center rivet. OK
Click to expand...

It does not have a rivet.

A1ZLKgYORWKFboDI0+Ifwg.jpg
 
AUSMHLY said:
... I tested the Lucas Sports Coil with an ohm meter, it's reading 3.1 ohms. ...

...

What should I check, and how?

What caused this problem?
Click to expand...

Did you get the 3.1 ohms across the primary terminals? Did you check the primary->secondary circuit for impedance? This is stretching my theoretical electronics knowledge, as I've never checked secondary impedance on a coil, but the primary and secondary coil windings are insulated from each other (spark is created by the primary windings inducing an EM field in the secondary windings, which creates the high voltage when the primary current is interrupted and the secondary windings' EM field collapses). The only thing I can think of would be a dead short between the primary and secondary windings--i.e. the insulator, oil I think in Lucas coils. has shorted--allowing a constant 12V current through the Pertronix, coil, distributor cap and rotor. I've never had a Pertronix fail outright, but I would expect its power transistor would fail open in a few milliseconds, but a few milliseconds might be enough to create this damage (as anyone who's ever dropped a wrench across a 12V car battery's terminals can attest).

Of course, we can't see what the cap's center electrode looked like before it fried, but I wonder if the Pertronix cap and 'stock' Lucas rotor are mismatched somehow?
 
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