Today I started putting decoders on LL GP-20 frames and trying to fit the frames under Bachmann F-7 shells. I "finished" three this afternoon--an A and two B's. Quick observations: The decoder installation is straightforward, although you do have to disassemble the frame completely. I decided to leave the tabs on the motor brushes, as I've found removing the brushes is a pain. A heat sink protected the brush housings. There's plenty of room under the F-7 shells so no frame milling was needed. I used TCS M2 decoders. Re-assembly is fairly easy, but everything has to go back in the proper orientation. It's easy to reverse the plastic motor cradle. The decoder will fit along the side of the frame too. Weights will fit in the "back" top recess. My A-line weights were just a tad to thick to fit along the sides, so I'll get some thinner ones. Fitting the shells is a little tricky. For now, I decided to use the bigger GP-20 fuel tank. I ground off the air tanks. The shell sort of snaps on once this is done. I have Kato fuel tanks, but that will require some grinding to fit them--I didn't have time today. This was good enough for tests. Couplers are going to be a pain. I took a quick and easy route. I glued a 1015 coupler into the nose of the A unit. One shim on the bottom, two on top. I think they were .020, but may have been .040. My units are going to be a permanent ABBA. For now, I made drawbar units with a piece of small gauge insulated wire. I drilled holes in the end of the shells, and AC'd the wire between them. Good enough for now. The Bachmann stirrups interfered with the trucks--I thinned them on the inside. This won't work, so aftermarket stirrups are next on the shopping list. The trucks also interfere with the front pilot--I wedged the new A unit frame back as far as it would go with a styrene block. It still may interfere, requiring some surgery. I still need a way to more securely attach the frame to the shells, and to keep the shells from fouling the pickups. The deck of the GP-20 did the latter--I may try cutting it down to fit under the shell. The three units run great on straights, but will need some of the tinkering described above to become part of my fleet. Pictures? Maybe next weekend. I will cross-post this to the DCC forum.
Well, here they are: As I did more of these installs, I got better at it. It seems the first one I did had a slightly warped shell--the stirrups were bending inward. By shimming it out, the stirrup problem went away, at least on my 18" radius curves. I also used a piece of styrene to jam the mechanism all the way back on the shell, so the front pilot interference also went away. I took out the mike and found I was using .025" shims to fit the front coupler--one shim on the bottom, two on top. I'll rig up some drawbars to replace the wires now connecting units. I may try the next consist with one decoder picking up from all four engines. I need to get a better amp reading, which means I have to install my Rampmeter.
