Spark plugs for 1925

 Hello, just purchased a 1925 Hudson. Would like to put new plugs in. Any one know of a longer plug? Has Champion D21 at 1/2” reach. 


  • ESSX28-1ESSX28-1 Posts: 1,399Senior Contributor
    The Green Spark Plug Company in England sell a 18mm long reach plug "KLG ML 50"
    I use them in my Essex Coupe with great results
    Dave Y  New Zealand
    Dave Y New Zealand
  • HansHans Posts: 256Senior Contributor
    AC W,   is the long plug for Hudson and some Essex engines.  It is a hotter plug similar to the Champion D21  while the D 23 is the hottest then available.

    Be careful, there is a little newer AC plug labeled AC W but is a very cold plug - physicaly shorter  and with a side pin for racing service. there are some on ebay

    Other plugs with a long reach are Champion 9Com  ( Com for commercial)
    AC 88L-Com
    Autolite B11

  • GeoffGeoff Posts: 4,605Senior Contributor
    There was a plug put out especially for David Brown tractors which were champion  7-Com-L, with two ground electrodes.  I bought four sets in 1960, and have used these for 60 years, still  have one set left!  I'll be 120 years old by the time I have used the last set!
    If you are going to change to long reach plugs you will have to run  a tap down  the threads to clean out the carbon, and you must check that the plug will not extend beyond the threads.  If they do two things can happen, the  valves will hit the plugs,  and the plug threads that are exposed will carbon up and you will not be able to remove them.
    If you're stuck in a hole, stop digging.
  • 25truck25truck Posts: 49Member
    I run the Champion D21 in my car with great success.

     I’m not sure how much longer of a plug you want run. but do  know that running a plug longer than originally equipped with from the factory is also like adding timing to the engine as the flame front is started deeper in the combustion chamber.

    just my experience from working on race cars for a living.
    It may have little effect on a engine with such low Compression.


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