Hemi Spark Plug Question

Electrical & Ignition

  1. cobrat93

    cobrat93 Member

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    Hi all,
    I have a question about spark plugs for a 426 Hemi. I'm told by a coworker that I should remove the crush washers from the plugs before installing them. Just curious if this is true or what your guys opinion is about the subject? The plugs I removed that were installed by the engine builder were Autolite 3924 and still had the washers on them. My concern is whether the plug tube is sufficient enough to seal off the combustion chamber or not? Just wondering what the general consensus is?
     
  2. R413

    R413 Well-Known Member

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    I’ve asked many people this question and get about half and half with the answers on it.

    Would be good to look at a head off the engine because the washers will affect how far into the Combustion chamber the plug goes.

    I think the tubes would get worn away without the washers and changing plugs. I used the washers and engine seems to run great.
     
  3. chooch

    chooch Well-Known Member

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    I've always removed them from what I was told they are not needed since there are the tubes & the washer just split the bottoms out of the tube.
     
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    • RJRENTON

      RJRENTON FBBO Gold Member FBBO Gold Member

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      IMO...
      The FSM says to remove the washers and the tubes will act as the washer. This will allow the tube to draw down and the O-ring at the top of the tube will seal to the valve cover and prevent an oil leak. The origional plugs were Champion N-10Y which were a cold range. Most dealers usually installed Champion N-12Y plugs to prevent cold fouling, when the vehicle was brought in for poor running and missing operation......back in tge day....
      BOB RENTON
       
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      • R413

        R413 Well-Known Member

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        Leaving the washer on the plug will not change the position of the Spark plug tube in the valve cover or head.
         
      • RJRENTON

        RJRENTON FBBO Gold Member FBBO Gold Member

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        The overall installed length of the installed tube is increased by the thickness of the plugs aluminum washer, assuming that the washer is placed on the plug after the plug was inserted in the tube..... I guess it depends the mechanic's methods......just a thought...
        BOB RENTON
         
      • R413

        R413 Well-Known Member

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        Bob, to put the washer under the tube is crazy. The oil leakage would be substantial from the tube and valve cover area, like flowing out everywhere above idle speeds.
         
      • RJRENTON

        RJRENTON FBBO Gold Member FBBO Gold Member

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        Yes....absolutely agree....but...ive seen it done that way....obviously incorrect snd wrong....who knows why somethings are done wrong.....
        BOB RENTON
         
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        • cobrat93

          cobrat93 Member

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          I was thinking the same thing in regards to the bottom of the plug tubes getting worn/distorted without a washer on the spark plugs. There was a tad bit of oil in the bottom of each plug tube before I removed the plugs and it huffed alot of blue smoke when I fired it up after installing a new set of plugs but I think I'm going to pull them back out again and remove the washers and see what happens.
          Thank you for the advice!
           
        • Fran Blacker

          Fran Blacker FBBO Gold Member FBBO Gold Member

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          Can't help oil running into cylinders that's why they make spark plug tube seals.
           
          Last edited: Jul 31, 2020 at 6:43 PM
        • HD539

          HD539 FBBO Gold Member FBBO Gold Member

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          I remove the crush washer. Don’t know if it makes a lot of difference but I believe the service manual recommends it.
           
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          • tonysrt

            tonysrt Well-Known Member

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            You need the inserts installed in the head to prevent the oil going into the combustion chamber. Milodon makes them, they are metal inserts and stay installed in the head. I have them on my hemi and it solved that problem.
             
          • cobrat93

            cobrat93 Member

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            I want to thank everybody for your responses!
            I installed a set of stock heat range plugs back in it, removed the washers and took it for a spin, seems happy so far!
            Again, Thank You All so very much for the advice!
            Keith
             
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            • snakeoil24

              snakeoil24 FBBO Gold Member FBBO Gold Member

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              Guys speaking from experience on Hemis, no gaskets on the tubes please. The tubes stretch already on their own. The gasket on plug will tear the aluminum tubes. Putting the o ring seats in the heads will help a little but you still will get oil down the plug tubes. Remember the gaskets at the top of the tubes will into the valve cover and also will cave ina small amount. The method of sealing the Hemi plugs at best is not very good. These motors were not meant to run the same set of plugs very long and will still leak.
               
            • mrhemi

              mrhemi Well-Known Member

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              I have been removing the washers as per the FSM for 40 years with no problems.
               
            • Road Rat

              Road Rat FBBO Gold Member FBBO Gold Member

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              I remove the washers, and yeah the well that the plug and tube go into has oil in it on my old street Hemi. The new engine has recesses machined in the head for o-rings that fit snug around the tube, no oil in them.
               
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