365 GTC/4 distributor cap contacts | FerrariChat

365 GTC/4 distributor cap contacts

Discussion in 'Technical Q&A' started by Bryan, Jan 25, 2004.

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  1. Bryan

    Bryan Formula 3

    #1 Bryan, Jan 25, 2004
    Last edited by a moderator: Sep 7, 2017
    My 365 GTC/4 has been running rough and the exhaust smelled like rich fuel. The right side exhaust appreared to be the "rich side." The carbs have been reasonable, so I looked to the ignition. Using a timing light on each plug wire indicated that the left side was fine, but 2-4 cylinders on the right side were erratic to no firing at all!

    I pulled the distributor cap and tested the resistance from the distributor cap to the spark plug connection. Connection was not very good on several wires.

    The individual contact on the inside of the distributor cap appeared black. Light sanding with an emory board produced the results represented in the attached photo.

    There appears to be a slight (fractions of a mm) "crater" in the face of each distributor cap contact face. I attribute this to the contact on the rotating distributor shaft. Is the "crater" (which is still slightly black with carbon) good enough or is there a way to remove all signs of carbon? I assume I should not sand the contact faces too much. Comments?

    By the way, I reinstalled the cap and the car runs much better and the timing light indicated a strong ignition signal across each spark plug wire.
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  2. jselevan

    jselevan Formula 3

    Nov 2, 2003
    Bryan - the rotor should not make contact with the individual spark plug lead contacts. There is a few thousands of an inch clearance that provides a close enough gap for high voltage to jump across this small gap. The "crater" is likely brass erosion resulting from millions of sparks slowly eroding the metal.

    I would remove the cap and unscrew the pointed brass screw that holds each of the wires in place, clip off approximately 1/2 inch of spark plug wire, and reinstall after treating everything with silicon spray. You might consider replacing the wires, as with time the resistance increases. Oh, and don't forget to remove the center carbon brush and do the same treatment to the coil wire, the common denominator for all spark to the cylinders.

    For what it's worth.

    Jim S.

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