CB&Q M-4a Project Part 2: Surgery

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The LMB boiler required extensive modifications to make it fit over the Walthers mechanism. The boiler is designed to fit over a motor mounted in the cab. The Walthers motor and weight sits further forward, as typical for more modern mechanisms. I used a Dremel cutting wheel to enlarge the cutout just ahead of the firebox, taking a little off at a time and test fitting the Walthers mechanism until everything fit together without interference. I also removed some of the boiler-mounted details to make access to the area easier. These will be replaced later.



Photos show the cylinders of the M-4a are centered on the smokestack, and that’s how I positioned the mechanism along the boiler. This left a space between the rear end of the Walthers frame and the rear endplate under the LMB cab. I used heavy styrene strip to build a frame extension, shaping it to approximate the side bearers of the trailing truck. This assembly also serves as the mounting point for the drawbar. I attached it to the metal frame using both glue and a 2-56 screw to ensure it can support the drawbar forces.




I found a brass Delta type trailing truck on E-Bay that matched type used under the M-4a’s and was better detailed than the LMB version. It fit nicely with only slight modification to the mounting pad of the original Walthers trailing truck.


I also replaced the tender trucks with plastic versions of similar Commonwealth trucks from Rapido that have power pickups from both rails. I had to lower the bolsters to match the height of the mounting pad of the LMB tender.



The last major modifications were to the drivers to replicate the unique disc main driver and heavy counterweight on the 4th driver. I made styrene overlays for these two drivers. When painted, they look very convincing.




I was very happy with the results of these modifications. I “ran” the engine on the layout by pushing the freewheeling mechanism with another engine to check for any binding or clearance issues. It was now ready for details and decoder installation.






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