HEI coil fails

[RPM]

A good friend of mine has a 34 sedan with the everyday run of the mill 350. This car has been up and running for several years with no problems. Several weeks ago the running fine going down the hwy and it just quit running. A new MSD coil got it running again. A week later it dies, bad coil. So he buys a new complete Mallory HEI distributor and installs it. A week later it dies. 3 coils in 3 weeks. Check alternator output 14.3 volts. Rechecked for loose grounds. Mallory and MSD have no idea, or won't say. The carbon button is installed as is the ground strap inside the cap.

Anyone got any ideas?

 

[putz]

Did he install a new cap also I have seen carbon tracking burn out coils before.

 

[Mike]

How does the carbon button look? You can get some arcing in there that will start eroding the button and overheating the coil. Is the carbon button installed ahead of the insulator? If not, you're arcing from the button to the rotor strap. I always like to give the rotor strap a tug up, before I install it, particularly with MSD pieces in the system.

Where is running voltage at 2,500 RPM? Anything over 14.6 is getting into the danger zone. I'm betting this is the problem, since a new distributor is causing the same problem. Is the ground strap a new one? It needs to be bright and shiny.

High quality rotor? A cheap rotor can eat up an HEI coil, but you can always see the burning on the rotor. I am really a big fan of Echlin's caps and rotors, because you know you're going to get something with brass contacts, rather than aluminum. Run some cheap aluminum contact stuff and you'll soon learn why aluminum oxide is used on sandpaper.

What have the weather conditions been like? A lot of humidity?

Adding the MSD external coil kit to an HEI is a really good idea, because it gets that heat source away from everything else. Any time you can use an oil-filled coil cannister, as opposed to an epoxy-filled coil, you're going to be letting the coil run a bit cooler.

 

[putz]

I have seen holes burned right through rotors more time than you can count.Especially the cheap ones have had good luck with Echlin also.