I think the difference you see between your motor and other Lionel worm drive motors is the brush tubes. The first of these motors were in the postwar 726 and 671. They are distinguished by the die cast front mount, which is long enough to mound two sets of bearings it. That is two radial bearings and two thrust bearings. The dual radial bearings allowed Lionel to stop using the brush plate as a bearing and allowed them to install thrust bearings that are required to handle the axial forces from the worm drive. This motor went though three different designs of the brush tubes. The first design used a long compression spring retained in a tube, which screwed into the brush plate. This design is distinguished by the screw driver slot in the of the tube. This was quickly replaced with a nearly identical brush tube that was crimped into the brush plate. In this design the screw driver slot is gone. This was replaced by a stamped, rather than machined, tube with a torsion spring. On this change the silver plating also disappeared. This final design was used for many years right up to the can motor and is by far the most common. I believe these three design changes were driven by “value engineering”.
Your loco has the second design, which is the poorest from a maintenance standpoint. In this design the only way to inspect and service the brushes is to disassemble the motor. The locos shell must be removed, The field wire unsoldered from the brush plate, and the two brush plate screws removed to get the brush plate off. To reassemble the motor the brush springs are slipped into the tubes, the brushes are assembled on the ends of the brushes. The locomotive has to be lowered onto this so the brushes and springs do not fall out. Brush and commutator maintenance are important because in my experience there is no faster way to ruin a motor that running it with no spring tension on the brushes. This can occur be cause the springs are bad, the brushes are stuck in the tubes, or they are too short. The commutator also needs attention. Power comes to the armature by coming in one brush, though the commutator segment, into an armature coil, out a different commutator segment, and out the other brush. The motor gets it power from the current that flows through the armature coil. The carbon brushes are soft and they wear with use. Some of that carbon dust gets into the slots between the segments. Since carbon is conductive the carbon dust in the slots can shunt some of the current from commutator segment to commutator segment bypassing the armature coils. This reduces the current in the armature coil, thus reducing the power output of the motor. Lionel took this problem so seriously that they provided a pointed stick in their maintenance kit to clean the slots.
A good guide for servicing any postwar worm drive steam locomotive is an article that Dennis Waldron wrote. His article is written specifically for the 773, but with only one major difference it equally applies to the 726. The difference is that the 773 has an intermediate shaft between the motor and the drivers. In the 1947 and later 726 locomotives the worm gear is on the end of the motor shaft and drives the worm wheel pressed on the axle. In Dennis’ article just ignore the worm shaft, bearings, and coupling. They are not there in the 726. Dennis’ article can be found here:
https://www.justtrains.com/Hudson/773-1.asp
The 726/736 were made for many years, maybe on and off for almost 50 years. Many parts used in the 726 came from prewar locomotives 700E and 226. As a result of this 726 parts are still plentiful and easy to find. After you figure out what you need I would suggest you contact either Jeff Kane, The Train Tender, or Dennis Waldron, at Just Trains for any parts you need.
