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