4-6-0 Problem

[Max]

I have just bought a new 4-6-0 in On30 scale, Item #28697 which is DCC ready. No sound.
The loco runs very smoothly in reverse but has a very distinct "bind" or "lurch" in forward.
I've checked and cleaned the worm gear, idlers and axle gear.
All running gear seems to have ample play when checked at the point of "binding".
Have tried both DC and DCC. Have tried a new Lenz decoder.
All with the same jerking in forward result.

Could this be an electric / electronic problem ?
could the resistors and/or capacitors on the motor cause this problem ?
Any advice will be gratefully received.
Thanks, Max.

[Jim Banner]

What you describe sounds more like a mechanical problem than an electrical one.  Sometimes there is a bit too much end play in the motor, allowing the armature to slide back and forth.  The worm working against its pinion causes the armature to move forward for one direction of the locomotive and to move back for the other direction of the locomotive.  Just which way it goes depends on whether the worm and pinion are cut left handed or right handed and whether the worm is above or below its pinion and whether the motor sits in front of or behind the drive axle.  Usually, the worm is right handed and above the pinion and the motor is behind the axle.  This means the armature in the motor is pulled forward, away from the brush end of the motor when the locomotive is running in reverse and is pushed back when the locomotive is running forward.  If the armature moves back too far, the brushes may jam against the uncut section of the armature causing jerky operation.  The rearward motion is normally controlled by the rear bushing or the part of the plastic end cap that serves as a bushing.  If the bushing is too short or in too far or the end cap is loose or the tabs that hold the end cap to the can/case are not bent far enough or the thrust washers are missing or the wrong size or ... well, you get the idea.  A lot of things can go wrong and cause a binding problem.  Sometimes you can feel the problem by removing the motor from the locomotive and turning the shaft back and forth while applying a bit of tension on the shaft, first toward one end, then toward the other end.  The motor should turn very smoothly in both directions and with tensions both ways.  If not, you have found your problem.  The easy repair at that point is a new motor (installed by either you or Bachmann.)  The old motor is generally repairable but requires tools not generally found in the modeler's tool kit.

I don't know if it is any consolation or not, but years ago that was one of the commonest complaints about model steam locomotives - that they would run well in reverse but not forward.  Nobody ever seemed to have the problem of running well forward but jerking in reverse.

Jim 

[the Bach-man]

Dear Max,
Run your loco forward at moderate speed until it breaks in. If, after twenty minutes or so of running time it still binds, contact service.
Thanks!
the Bach-man