Do MSD boxes burn up cheap Caps or what the heck is up with my HEI

I have a customers car with HEI installed on it here at the shop with a 350 SBC. For some reason it is melting/burning a hole in the distributor cap right where the tach and power hook up. It looks like it is the Ground strap doing it? Any ideas what is going on? I've heard it can be cheap autopart store caps when used with MSD. This car has MSD. I thought it might be a short in the power wire. But when I think about it, it doesn't make sense and it checks okay.... I replaced the cap, because it was melted with a good used I had just to see what would happen and the new one did it immedietly The owner said he replaced the cap "a few months back" and it looks newish. Any ideas? I'm waiting for my battery to charge on my camera to take a picture.

 

I'd start by downloading the instructions from the MSD web page, and see if the MSD stuff was installed correctly.

 

That and making sure that the particular model of MSD on his car is compatible with an HEI.

Grounds? Is the ground lead from the coil connected and is the connection where the plug goes into the cap tight? I've seen several HEI's that had the lead that goes from the distributor to the cap have it's hold on clips broken for one reason or another and that could cause a less than stellar connection on the leads.

 

Sounds like the female conector in the plug is not making good contact and the added resistance is making heat and melting the cap.

Larry

 

Bear with me guys battery is almost charged....It looks like it is coming from the ground strap in the cap? I'm going to clean up the grounds and go from there....to be honest the wiring under here is hacked....

 

Found the MSD instructions in the car.....looks like the black wire that is routed with the orange wire(b+) should go to (c-) but is hooked up to the tach signal?

 

Got the wiring figured.....It's arcing between the power and ground strap.....Has anyone had a problem running a cheap replacement HEI distributor cap on a SBC?

 

I always use an Accel cap 'n rotor. Where that falls into the cheap scale I'll let you decide, but it is the only one I can readily get that has brass terminals. I've used "cheap" aluminum terminal caps in the past and they where short lived, so back to spending a few bucks more for the Accel.

Alex.

 

Maybe your coil is over heating, they are known to do without any outside help.

Probably not the answer or solution to your problem but something to think about.

 

I wounder if the metal ground strap that fits under the coil is missing?

 

Thats what I was thinkin.

 

It's there....where it goes into the cap by the power and tach hookup is where it is arcing.

 

where it is melting

 

Thats high voltage trying to find its way to ground, Ohm out or replace the spark plug wires for both towers in the pic. A bad high resistance wire will raise the voltage required to fire the plug... problem is the spark finds it's least path of resistance back to ground.

 

Make sure you are using the right coil button. If I remember right you cannot use the carbon style button with an MSD, you have to use the copper one. Using the carbon one will result in too much resistance, and melted caps.

 

Now that is interesting. It definitely has a carbon coil button.

 

Yeah I believe with the box, or maybe just the MSD cap/rotor, it comes with both. It's been a while since I looked at it, I swapped out my HEI for an MSD Pro Billet in my Chevelle a few years ago.

 

Start by getting the right button. I beat my head against the wall for about a week on my first MSD on an HEI car. Summit can hook you up pretty cheap.

http://www.summitracing.com/parts/MSD-8412/

Okay...so not so cheap.

 

New low resistance button fixed the problem.

 

Cool you get it sorted out. Another tid bit to go in the note book.

 

Hopefully this saves someone some trouble.

 

That is the whole idea.