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RE: [O-14] Re: Dunkirk/Athearn Chassis AGAIN

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  • Frank Sharp
    A few days ago I posted a method of regauging the Athearn SW-7 chassis for a Boulder Valley Dunkirk to 14mm gauge. I have since had a further play which
    Message 1 of 5 , Nov 1 7:09 AM
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      A few days ago I posted a method of regauging the Athearn SW-7 chassis
      for a Boulder Valley Dunkirk to 14mm gauge. I have since had a further
      'play' which retains some of the compensation. For completeness I'm
      repeating bits of the original posting

      The Dunkirk kit tells you what modifications are required to make the
      chassis fit and how to get it apart. The chassis comes with a full parts

      Strip it down, including removing the motor, just pull and the mounting
      pads pop out. Remove the two copper springs (watch the brush springs)
      solder wires onto the clip part at the brush end and put them back, but
      onto the opposite sides to where they started. This gives connections
      for DCC but breaks the chassis connection. I prefer 'dead' chassis even
      if I wasn't using DCC.

      Pull wheels out of gear/muff. Find a nut 2.5 to 2.7 mm thick and use it
      to force the wheels further onto the axle leaving therefore about 2.6 mm
      of axle on the outside of the wheel. Alan Gibson does some washers for
      1/8th inch axles, a packet contains 10 each 1mm. 0.5mm and 0.25 mm
      thick. Just run a flat file over a 1mm and a 0.5mm to take off any
      burrs. Slip then on an axle and push it back into the muff, do the other
      side, instant 12.45 back to back.

      Drill or grind out the tube rivet that holds the metal side frame and
      remove the side frame, discard rivet. I pulled out and cut all four of
      the metal strips which are on the inside to a height just below the bend
      on the shortest side, cleaned and straightened them up, they are
      distorted, presumably when the rivets were fixed, and then soldered
      wires to them. Open out the holes in these strips, the holes in the
      plastic gearbox where the rivets were and the central hole in the metal
      side frames to 9/64ths of an inch. Clean up all burrs. Take 4
      Branchlines 1/8th to 1.5 mm adapter bushes and tap 10BA, clean up so
      there are no burrs.

      Take the oil retaining bushes from the axles, soak in MEK to remove the
      oil and solder into the recesses in the metal side frames. Fit them
      right up to the top of the cutouts, and flush with one face of the
      frames. Though it doesn't affect how you solder them they are going back
      with the protruding part of the bushes outboard of the frames when you
      reassemble. At the same time solder a Branchlines 1/8th bore top hat
      bearing into the enlarged hole in the metal side frames. It should go in
      from the outside so that the flange sits hard down on the outside of the
      frame. Make sure you solder it square.

      Put one metal strip with the soldered wire back in place, and pass a
      10BA bolt through a 10BA washer and then through the hole in the strip
      from the inside. Push a Alan Gibson 2mm bore main frame bearing, part no
      4M65 over the bolt from the outside, flange out and push it through the
      9/64 hole until the flange rests on the plastic gear box. Take an Alan
      Gibson 2mm bore 1mm thick washer, deburr the faces on a fine flat file,
      and slip it onto a wooden cocktail stick. (Tesco own brand are just
      right size) Just run a fine file around the outer edge until the washer
      will slip inside the top hat bearing without binding. Put this washer
      onto the 10BA bolt, slide the top hat bearing soldered into the metal
      frames over it, and tighten the tapped 1/8th to 1.5mm flange out onto
      the bolt.

      The frames should pivot freely, but not too slack. If it is too slack,
      thin down the 2mm x 1mm washer.

      Do the other side of the gear box and assemble, slipping the axles into
      place as you do it. If when you reassemble the wheels are rubbing on the
      metal frames put a 10BA washer between the AG 2mm main frame bearing and
      the 2mm x 1mm washer. I've had to do this, but I think it is because I
      have replaced the disc wheels with spoked wheels.

      Now the metal side frames should be able to pivot, giving some
      compensation to the chassis. They may benefit from being cut down a bit
      so they don't show too much behind the cosmetic diamond frames

      I've had it running with a DCC chip lashed into place. I've had to wash
      all the chassis parts to get rid of swarf etc, so it needs reoiling (
      plastic safe oil I assume), but it is crawling round without problems.

      Oddly, now I've got the chassis sorted I wondering about the Dunkirk.
      The interior is along way from the original in order to cover the
      Athearn chassis. I'm wondering if it can be done properly or nearly
      properly with Grandtline gears and universal joints. On the assumption
      that I will now use the chassis elsewhere than the Dunkirk I have
      extended the axles on one bogie, added Sharman's small tear shaped
      outside cranks and coupling rods.

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