Distributor Cap Issues

[sharkx]

Can somebody tell me what is going on here? The engine started breaking up at anything over 2,500 RPM. After checking the usual suspects, I pulled the distributor cap, I noticed that the carbon contact in the center is completely missing. There's a hole about 1/2" deep where the carbon contact was. In addition to the grey deposits, there are signs of arcing as well as a black soot like material on the inside of the cap.

The center section of the rotor that's suppose to be in contact with the carbon contact has been eroded away to just a stub.

I'm running a .035 gap on the plugs with newer wires. The cap and rotor have less than 3,500 miles. The ignition is a MSD 6AL

This this typical or is something else not right? I replaced the cap and rotor and all is well for now.

Thanks,
Bruce

[Bob Taylor]

looks like a moisture related thing, somewhere they may be a thread about a swipe of silicone sealer where the cap meets the dizzy. the inside of the cap looks wet to me . I uise the MSD cap and rotor "kits" on both my Ford dizzy's and have no issues. I live where its very moist Bob

[ROADRACER83]

Are you sure that is the right cap? I have never seen a Ford style cap that had those Chevy bent "L" type hold downs.

The Ford style I am used to has a curved spring steel spring that clicks into a recess on the cap itself on the large diameter caps. On the MSD small diameter distributors, there are two screws that hold the cap on. The cap you have is full of melted metal so maybe the center carbon connector just broke for some reason and let the spring connector on the top of the rotor to contact the top of the cap. Also, there is a spring up in the cap that pushes the carbon contact down toward the rotor. I don't see that spring anymore. This is more than just the usual moisture problem that the caps get.


Ron

[Useless]

Looking at the cap it does not look good when you go back together do not use so much sylicone on the cap conection spots

[sharkx]

It's the right cap. The distributor is a MSD Pro-Billet for a Ford FE which uses the GM style L type hold downs.

I neglected to mention that there was a small piece of slag sitting in the rotor, I'm guessing that was the remains of the spring.

Bruce

[ROADRACER83]

Originally Posted by sharkx

It's the right cap. The distributor is a MSD Pro-Billet for a Ford FE which uses the GM style L type hold downs.

I neglected to mention that there was a small piece of slag sitting in the rotor, I'm guessing that was the remains of the spring.

Bruce

Bruce: I had not seen those hold downs before. I think that the cap was just defective and the carbon center contact either broke or somehow came out and started a chain of destruction inside the cap. MSD seems to be having some QC problems lately.

Ron

[convincor]

Its actually pretty common with the MSD cap/rotors.
The problem starts with the contact on the rotor not being bent high enough to make contact with the center pin of the cap. This causes arcing across the gap which isn't supposed to happen resulting in it burning up...
Replace cap and rotor and bend contact up on the new rotor to be sure there's good contact.

[edwardb]

Originally Posted by convincor

Its actually pretty common with the MSD cap/rotors. The problem starts with the contact on the rotor not being bent high enough to make contact with the center pin of the cap. This causes arcing across the gap which isn't supposed to happen resulting in it burning up...
Replace cap and rotor and bend contact up on the new rotor to be sure there's good contact.

Yes, I also just learned this is a common problem. I have the MSD SBF billet distributor, 6AL box and Blaster coil. While checking a few things on my Roadster just last weekend, I too found the little carbon button worn off completely flat. Not quite 1000 miles. In looking at various forums and MSD responses, their answers were either broken or damaged carbon button (e.g. shipping damage, mishandled, etc.) or not making contact and burning up due to arcing. MSD recommended applying some dielectric grease on the rotor contact, and setting the cap in place to confirm it's making contact. Bend the tab up if needed. Fortunately I had a spare cap and rotor on hand. Did the test, made sure it was contacting, and I will be watching closely. The car had been running OK before, so no symptoms (yet). But seems to run a little better now.

[Todd Buttrick]

I had the same vanishing button phenomena on an Accel dizzy with he same type of GM cap/rotor. I've gone through about three sets. If it wasn't the cap itself, it was the rotor. The last rotor broke the wiper arm retainer so the arm was skewed and built in 30 degrees of retard timing. Yup, ran like crap. I pulled the whole mess and replaced with Summit dizzy #SUM-850312-1. Screw down cap and rotor is the only thing I'll buy going forward. Gotta be the same company making all those caps.