I didn't know that USA Trains stopped making the 44 ton motor blocks. They do sell replacement geared wheel sets however. Both with and without traction tires. I imagine these wheel sets to be the same ones used in some of their other locos. I opted for the plain wheel sets, without tires. I feel that the tires may have something to do with the premature splitting of the plastic portion of the axle.
USA Trains makes some very nice trains. Beautifully detailed locomotives and rolling stock. However, the engineering design of how the parts all fit together leaves something to be desired. I've worked on many LGB locomotives and tearing them apart and reassembling them is straight forward. USA Trains locos, on the other hand, are more difficult to disassemble and reassemble. Access to the screws holding things like upper body parts to the chassis requires a screwdriver that hasn't been invented yet.....

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When I disassembled the 44 ton loco, I found that one of the posts inside one hood was broken off. These posts member up with a female post that is part of the chassis. This seems like a weak design to me. Getting to the screws that hold the hood onto the chassis is difficult, requiring that uninvented screwdriver I mentioned. The drive axle design is another mystery. Why it was designed this way is beyond my comprehension.
While it sounds like I am trashing USA Trains, I'm not. Many modelers are quite pleased with their products. Their Overton coaches are some of my best operating rolling stock. I'm hoping to get many years of enjoyment from my 44 ton loco.