MSD Distributor Cap

[601HP]

Those of us in this hobby who are MSD users know of the issues with these caps. Here's my recent finding.

During the Rehoboth Fun Run Oct. 5 & 6, Peggy and I were raising a lttle heck here and there. Sometimes I thought I was down on power during WOT , but I was still able to raise the thrill factor substantially. There was no missing or stumbling, but the tire-shredding factor seemed mildly diluted.

Jumping ahead.............

Yesterday I was just about ready to take a Sunday afternoon drive, but decided to check inside the distributor before the drive. I half expected a mechanical advance problem. What I found was....
a. The carbon ball in the top of the cap had broken off.
b. It was growing little green thingies on each of the 8 contacts.

That cap is about 4 years old with about 4,000 miles on it.

My new cap will probably arrive tomorrow. I'm fairly certain this won't be the last cap I have to purchase!

David

[FWB]

you got twice the mileage i get out of them

[carmine]

If the carbon tip in the middle inside of distributor cap is worn out thats an indication that it was arching.
The reason for the arching is because there is a gap between the carbon tip on distributor and the spring tab on the top of rotor.
The spring tab on the rotor should be bent upward so it applies about 1/8 inch of upward pre-load on to the distributor cap carbon tip.

By manufacturing a spring tab that just barely if at all touches the carbon electrode will allow your car to run good when new but the arching will prematurely wear out the carbon electrode.

You find your self changing these items quite often.

The cap and rotor on my car has 7000 miles on it and carbon electrode still has no wear on it.

Many shops know about this but fail to correct by pre bending rotor tab upward to ensure good contact with distributor cap carbon electrode.

Win win for distributor cap and rotor sales along with more frequent visits to your mechanic for those that rely on one.

[601HP]

"Many shops know about this but fail to correct by pre bending rotor tab upward to ensure good contact with distributor cap carbon electrode."

When I first installed it, I positioned the tab as you described. I should probably inspect this area more frequently. Hhmmmm...

I promise to install the new cap correctly!

David

[dcdoug]

I don't have a MSD, but I still replace my cap and rotor every year as part of a tune up.....

[ERA 778]

I think most of us have experienced the problem with this MSD cap & rotor. I just wonder, has anyone ever measured the correct height of the rotor contact above the plastic? It would be great to have this information so we could always be sure that we've bent it enough.

[carmine]

I bend the rotor tab just enough so that when I place the distributor cap in place
it will sit about 1/8 inch above distributor.

In other words you should be able to push cap down in place and when you let go it should spring up about 1/8 inch.

This tells you that the rotor tab is positively contacting the carbon tip in cap.

No arching can occur between rotor tab and carbon tip if they are in positive contact with each other, which equates to minimal wear over thousands of miles.

The brass tab at end of rotor arcs across the gap between brass tabs at each plug location on cap. It's these tabs that wear long before you could wear out the carbon tip in cap.

[CJ428CJ]

I bent the tab up on my rotor so it was making contact with the carbon tip on the cap. The tab seemed to hold the carbon tip in place just fine as I discovered several thousand miles later as I pulled the cap off to see how it was wearing and the carbon tip fell off into the distributor in the process. I've since switched to this Summit brand cap and rotor and haven't had a problem since. Summit Racing SUM-G5234 - Summit Racing® Distributor Cap and Rotor Kits - Overview - SummitRacing.com

Chris

[LG57]

That Summit cap and rotor are what I use. Found the originals all corroded and green when I got the car this year. It was occasionally backfiring because of the corrosion. Runs strong now!