Spark Plug Extenders - Who Makes a Good One?

Discussion in '308/328' started by moysiuan, Oct 27, 2019.

  1. moysiuan

    moysiuan Formula 3
    Silver Subscribed

    Nov 1, 2005
    I installed new wires and extenders on my Mondial 3.2, and have had in two instances after hitting a pothole the extenders slightly pop off the spark plug and cause a major misfiring.

    When I look at my old original extender, the retaining clip is much more robust, compared with the newer one I had sourced from Kingsborne in the US a few years ago for my spares inventory. Anyone know where I can get a replacement that has the better quality more robust retainer clip on it, I don't want to purchase from elsewhere if they are all made the way the Kingsborne one is, hard to imagine different suppliers for this type of component even ones in the yellow horsey box. For now using a couple of old ones, and of course they were located in the more difficult access bank of cylinders.

    Comparing OEM dist caps and rotors, it is clear that the reproduction parts are not of the same caliber. Must make a habit of inspecting parts more carefully before assuming all is well before installing.
    Image Unavailable, Please Login
  2. To remove this ad click here.

  3. BigTex

    BigTex Seven Time F1 World Champ
    Rossa Subscribed Owner

    Dec 6, 2002
    Houston, Texas
    Full Name:
    That s interesting.....I'm sure OEM was Magnetti Marelli?
    They are not an expensive part, although eight can add up

    There have been nightmares with after market caps and more often the rotor.
  4. yelcab

    yelcab F1 World Champ

    Nov 29, 2001
    San Carlos, CA
    Full Name:
    Mitchell Le
    Nobody makes a good one. I suggest you replace them with special wires that do not use extenders.
  5. Milkshaker0007

    Milkshaker0007 Formula Junior

    Sep 22, 2012
    Full Name:
    i'm currently using super performance ones at the moment, only about 8 months old in use so hard to tell how they will behave down the line.
    look good copies aesthetically.
    replaced due to misfire on one cylinder under acceleration
  6. Brian A

    Brian A Formula 3

    Dec 21, 2012
    SanFrancisco BayArea
    Full Name:
    1983 US 308 GTS QV
    It is my opinion that the Kingsborne extenders are considerably better than the OEM ones.

    Your photos show just how much smaller the Kingsborne spring is that holds the extender onto the plug. The spring on the OEM extenders is so large that it is a major point for arcing and burning holes through the extender. The Kingsborne redesign solves this problem.

    The Kingsborne extenders are very tight and require a very hard push onto the spark plug. You can feel it slide over the threads of the plug when pushed on fully. There is no way a Kingsborne extender will be dislodged from the plug just by hitting a pothole.

    Properly installed, extenders are better than any other method in keeping the conductor absolutely centralized down the spark plug tunnel.

    … If it is any consolation, initially I did not push my Kingsborne extenders on fully and experienced the same misfire problem you did.
  7. To remove this ad click here.

  8. Freddie328

    Freddie328 Karting

    Jul 29, 2013
    Herts, UK
    Full Name:
    Do you guys know what the correct resistance through extenders and leads is supposed to be?
    I bought a set of leads some time ago and think its time to check them.
    I seem to remember that I changed them as some read open circuit, but can't remember what the values were supposed to be.
    This is for an 88.5 UK spec 328.
  9. moysiuan

    moysiuan Formula 3
    Silver Subscribed

    Nov 1, 2005
    Good to know the smaller spring has some technical merit. But in my case, the extenders are not that tight a fit on all the plugs, the spring load just does not seem that strong. I am in Toronto, and you would not believe the potholes that we have here, and the correlation between a big hit and a plug misfire was in my two cases pretty clear. But in any event, I have carefully reseated all of the extenders, and shall see if the problem resurfaces again.

Share This Page