Home Forum Ask A Member Mark 25 key dimensions

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  • #8438
    captchuck
    Participant

      A bit of a fix because my Mark 25 slipped into gear while I had it above idle (way above idle). Trashed the woodruf key. Can someone give me the dimensions of the key? Obviously I can measure the thickness. What I need is the height and depth. To buy a key online would be $6 + $7 shipping. To buy from the local ACE is $1 but I can’t look it up with a merc part number.

      #66046
      chuckw
      Participant

        US Member - 2 Years

        part number is 20907

        #66051
        captchuck
        Participant

          Thanks but I am looking for the dimensions. The part number works when ordering something on line but I am going into the parts bin at ACE Hardware. Height and depth if anyone has their flywheel off. Oh, yea, it’s for a Phelon mag. I’ve got a Mark 20 but it has Scintilla so I don’t know if it is the same or not.

          #66065
          green-thumbs
          Participant

            US Member - 2 Years

            Whittle key stock to fit with a file. Height will be total depth of key way in
            flywheel and crankshaft or slightly less. Length and profile will be file to fit.
            As long as key ways ok this should work. KEY only locates relative position of
            flywheel to crankshaft. The lock up of taper between flywheel and crankshaft
            is created by proper torque of flywheel nut. Taper should not have any lube
            as the lockup is between dry surfaces.
            If taper surfaces are scored or uneven, they can be "lapped" to mesh using
            valve grinding compound…a process requiring patience. Remove all traces of
            grinding compound when done. Old school technique.
            Do not over torque (splits hub) or under torque (tears up key)
            In addition to being part of magneto ignition, the flywheel absorbs, stores and releases energy so power of engine is smoother. This means flywheel is under forces that
            lead and follow the crankshaft…if flywheel torque is insufficient the key takes
            a beating and may fail or batter the key ways in both crankshaft and flywheel
            Windy,but, important details.
            Good Luck
            Louis
            A small vise to hold key while filing is very helpful.

            #66070
            captchuck
            Participant

              Thanks Louis.

              With your explanation I’ll be able to get the dimensions right.

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