Bad forward / good backwards

On Mon, 11 Feb 2008 19:31:42 -0800 (PST), I said, "Pick a card, any card" and muselart instead replied:

If it's mechanical noise, check the surfaces of your worm gear. The direction or angle of pressure on the surface forward is different than backwards. If the noise is electrical, make sure your brushes are set correctly. Flat against the armature.

-- Ray

When a loco operates differently forward to backwards, assuming you've eliminated obvious intermitent actions caused by loose motor mounting, steam loco valve gear, trucks off the rails, cats sleeping on the tracks ... is that the armature of the motor will move longtitudinally due to the forces on the worm drive. One direction pulls the armature towards the brush/commutator end while the other pushes the armature to the back end of the frame. You'll be able to see this action with the top off the loco. There should be a small amount of movement, something like 0.5mm, which is a just visible movement. If the movement is more like 1-2mm (1/16") then most likely the brushes and commutator end curve are taking the load, resulting in uneven current flow. The fix is to fit washer(s) between the armiture and the motor frame. This normally involves taking the motor apart, but you can sometimes get away with making a styrene washer and cutting a 90 degree segment to make a "C" This can be snapped in over the armature shaft with care.

Greg.P.

Is it a Bachmann?

A lot of n scale diesels seem to be suffering from cracked gears and lack of lubrication.

It would help if we knew more than the scale; what mfgr., what model, new or older, etc.

fl@liner

It would be helpful is you elaborated in the type and manufacturer of this engine. Give us more details. At this point all I can say is that the problem is mechanical in nature.

Peteski