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Thread: Burned Ign rotor 70 911T

  1. #1
    Junior Member
    Join Date
    Sep 2015

    Burned Ign rotor 70 911T

    Attached are pictures of the Marelli rotor and distributor cap from a 1970 911T. These parts only have a couple hundred miles on them, They replaced a set with several hundred miles that were similarly burned albeit not nearly as badly.

    Engine is stock with the exception of an MSD box. Parts are from PartsKlassic. Kurt suggested checking the phasing of the rotor (which, even after reading what this is, I don't know how to do with this set up)

    Any ideas what could cause this level of degradation, especially with an electronic ignition I'd be grateful. Engine is currently apart.


    rotor burned.jpgcap burned.jpgGood Monday morning,

  2. #2
    Senior Member Scott A's Avatar
    Join Date
    May 2014
    My guess is that you have a bad ground.
    If a ground is out, then the ignition has to make its own ground. So it finds a new path.

    I think there are two grounds.
    One at the left engine area wall, one down at the transmission.

    And then sometimes those 14 plug connectors will melt and short out badly, they are in the engine area.

    Maybe there is a ground behind the engine fan too.

  3. #3
    Are you using the recommended MSD coil and cotton graphite spark plug wires? For rotor phasing I assume Kurt means basic TDC timing. Rotate engine to TDC of cylinder one firing stroke. Find cyl. #1 spark plug wire in the distributor cap, now mark that plug wire tower reference on the distributor body with a sharpie. Remove the cap, is the rotor tip lined up with that mark, or is it "out of phase" with the mark ie. not lined up with the sharpie mark.
    Early S Registry member #90
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  4. #4
    Member AKAMick's Avatar
    Join Date
    Sep 2018
    7750′47″S 16640′06″E
    Coil leads reversed, hooked up backwards?
    Current fleet, mostly rubbish automobiles and other assorted junk.

  5. #5
    Junior Member
    Join Date
    Sep 2015
    Thanks for the suggestions, We discovered the burned bits after pulling the engine for a reseal.

    Addressing what I can: The grounds were in place and clean, including the one behind the fan, but will double check when engine goes back in. Timing and point gap were spot on, connecting plugs are in good shape but, again, will be sure.
    Coil is recomended unit for the MSD unit. However, I've not hear of different wires. Can you elaborate? The original wires were replaced with repops (Stoddard, albeit with original sparkplug connectors because originals are 90 and repops are straight)
    Will check coil leads too--I can't remember last time that might have been messed with.
    Thanks again, RickO

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