Cap & Rotor question

I have a '91 XJ w/ approx. 199K on the ticker. I recently noticed it was running a bit rought so I popped the dist. cap and noticed some carbon build-up on the contacts in the cap and on the rotor tip.

I noticed the same thing on my old '88.

I've bought Mopar Performance ignition wires and a cap/rotor set to replace the parts that are on there now. NGK spark plugs will be going in also.

I was just curious what causes the carbon build up? Is a weak spark from the coil to blame?

use causes corrosion on the contacts. At least i have no idea how to avoid it btu thats why you do tune ups every 40k or so....keeps the engine running smoothe

Sounds like a normal wear and tear thing. Hit the inside of the cap with brake parts cleaner to rinse out the carbon, or better yet, take it in the house and slip it in with a load of dishes in the dishwasher. Better do it when the wife isn't home. They seem to have a thing about that and washing carbs in the dishwasher.

Distributors have no moving parts. Their failure mechanism is that a "short" occurs inside the cap. This is nothing more than the carbon or other material getting thick enough to allow the spark to either jump to ground or another terminal. A good cleaning is normally all that is needed. The rotor is much the same. The springy contact in the middle can sometimes lose its spring but thats pretty rare. Cleaning the rotor tip with a bit of sandpaper can remove any carbon buildup, just don't take any metal if you can help it. As you increase the gap between the rotor and the cap, the spark gets weaker. With todays high voltage ignitions, this is not nearly as big a problem as it was 30 years ago.

There are two types of buildup on cap terminals;

One type is ozone. caused by the spark jumping the gap... very normal and does not cause problems. usually a white powdery substance.

There is also a slight transfer of metals from the rotor terminal to the cap terminal, usually this shows up as a black carbon looking substance.. also very normal.

old_man said:

Sounds like a normal wear and tear thing. Hit the inside of the cap with brake parts cleaner to rinse out the carbon, or better yet, take it in the house and slip it in with a load of dishes in the dishwasher. Better do it when the wife isn't home. They seem to have a thing about that and washing carbs in the dishwasher.

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Yea, I've noticed 'The LOOK' if you take something out of the kitchen utensil drawer and head out to the driveway, usually results in a shadow attached to your shoulder. Borrowed a baster once to top off my battery with distilled water, will never make that mistake again...next thing I knew was my deadblow hammer was upstairs tenderizing chicken breasts..

Does brass fair better than other metals? Picked up a NAPA rotor, brass terminals.

mikeny59 said:

Does brass fair better than other metals? Picked up a NAPA rotor, brass terminals.

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In a word, YES. Much better than aluminum...

Accel makes a really nice cap and rotor set with solid brass contacts. It also looks a bit better than the stock black one.

Is that ACCEL cap and rotor in the ACCEL tune up kit? Where they supply the cap, rotor, wires, and plugs??

No it was just the cap and rotor by themselves. I got it at Advance. If i remember correctly it was relativly inexpensive too.