David Johnston posted:A few things I would check when I have a loco that likes to run in reverse, but not well forward. The motor brushes should be in good condition, proper length, end should be flat and square, they should move freely in the tube. The brush springs should have good tension and be the proper length. The commutator should be clean and smooth. The slots should be clean. Check the resistance from commutator segment to segment, total of three measurements. Should be approximately equal and between 1 and 1.4 ohms. The resistance from each segment to the shaft should be checked and should be very high to open circuit. 20,000 ohms or more would be good.
The 726 locomotives have a worm gear drive. The teeth on the worm wheel are at an angle. This results in the worm wheel pushing the axle sideways. One direction in forward and the other direction in reverse. This lateral force can cause wear on the axle bearings. With excess wear on the bearing the wheel can start rubbing the frame, causing the engine to run poorly in one direction. This problem usually results poor operation in the forward direction since most steam locomotives spend most time running forward. Inspect the wheels and frame for evidence that the wheels are rubbing the frame. This will probably be seen on only one side. This can be fixed by putting a shim on the axle to keep the wheel away from the frame. This can be an e-ring, horse shoe washer, or a cut washer. The other repair is to pull the wheels off the axle and replace the bearings.
Good luck.
David,
Thank you for your help on the 726. Commutator is clean, brushes and springs look good, clean, operating correctly.
But with OHM meter set to 200, I got 2.0-2.1 between two, then 2.0 between another two, then 3.6-13 between another
two poles, when I test each of the three poles to the to the motor shaft I get nothing?
Is my OHM meter set correctly?
Also when I roll the chassis back on forth on track with no motor, it seems very smooth?
Thank you for your help!
ncng
