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Dimensional Differences Between Knucklhead and Panhead Frames

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  • Dimensional Differences Between Knucklhead and Panhead Frames

    Hello!

    This is a question for a project that is a little more JockeyJournal than AMCA but I'm hoping that some of the detailed knowledge here will help me out.

    I'm currently in the process of building a 1953 Panhead Motor that is going into a chopped up frame (beyond being worth bringing back to stock). In taking some measurements I've found that the drop from the rear motor mount to the front motor mount is 1 19/32" which after measuring forum member chopsickles 47 knuck frame have determined to be the drop for a knucklehead frame and not the 2" found on Pan frames.

    I have done some extensive measurements between a friends Pan frame and my frame but have yet to come up with where the dimensional difference is between the two frames is that would cause the difference in drops.

    As best as I can tell, between panhead and knucklhead:

    -front motor mount casting is the same

    -rear motor mount casting is the same

    -Distance between the top of the rear motor mount and the bottom of the seat tube is the same

    -Distance between the top of the rear motor mount and the top of the seat tube is the same

    -The front motor mount is about 1/4" closer to the rear (along with 13/32nds higher)

    -The seat tube appears to be the same angle from level

    -Down tubes and cradle appear to have the same lengths and degree bends

    Most of these measurements were taken with a tape measure, straight edge and a angle finder so I may have missed something here.

    Any help would be greatly appreciated and hopefully it'll put me on track to still have the bike ready for Daytona in the spring time where I can buy any AMCA member who helps and is there beer or two!

  • #2
    Don't know if this will help but when I was a much younger man and used '55 or '56 straight legged Panhead frames for my Knucklehead powered choppers I always had to use a 1/4" spacer under their front motor mounts to the frame. I'm sure there's a technical (factory) reason for this but it's just what we did to make it work.
    DrSprocket

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    • #3
      THe Panhead engines were tipped further forward to give head clearance to the the rear head and seatpost tube.
      Be sure to visit;
      http://www.vintageamericanmotorcycles.com/main.php
      Be sure to register at the site so you can see large images.
      Also be sure to visit http://www.caimag.com/forum/

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      • #4
        If that's the only difference then it seems like it's better to cut and relocate the front motor mount instead of cutting, plating and/or stretching in the seat tube and back bone. Again, I'm only considering this because of the overall condition of the frame although it does still pain me to cut anything knuckle!

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        • #5
          That is they way Buchannan's Frame Shop did one for me back in the '60's.
          Be sure to visit;
          http://www.vintageamericanmotorcycles.com/main.php
          Be sure to register at the site so you can see large images.
          Also be sure to visit http://www.caimag.com/forum/

          Comment


          • #6
            Pansome,
            You might want to get in touch with either Steve Little at Race Frame or the guys at Wasco frame and see what they say. They are the experts on all things regarding frame and I'm sure have the dimensions on file. Rich and Chris have given good info too but the above do frame for a living. Might check around to see if you can make a swap with some one even if you frame is not perfct it still might be better and less costly than all the rework on the knuckle frame. Probably still need someone with a frame table to check any work for proper alinement. I know a couple of guys that have them and one has one of my 40-41 bent neck frames right now. Good Luck!

            Tom (Rollo) Hardy
            AMCA # 12766

            Comment


            • #7
              The front mount forging on a Knuckle is 3/8" taller than a Pan mount. The only clean way to do it is replace the mount.

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