Worm gear engagement

[Dgun]

I have a number of older Bachmann locomotives with the same problem. The motor worm gear will not stay engaged to the drive gear on the frame. I have tried shims but the hold down  on the motor doesn't seem to cope with the force needed to hold the worm engaged. Has anyone solved the problem in a satisfactory manner?

[brokemoto]

Which locomotives are they?   Are they SPECTRUM, Plus or Standard Line?

[Dgun]

The locos are al standard line.

[brokemoto]

Right, Standard Line......you have mentioned that they are older......What is the prototype?

F-unit?
Reading Company 2-8-0?
USRA 0-6-0?
GP-something(I forget which one B-mann did back then, a GP-38, maybe?--too modern for me)

There were others that B-mann did back then, but I forget what they were.

[Dgun]

I would guess the prototype would be the 0-6-0.

[brokemoto]

B-mann had several versions of these, over the years.  I have more than a few around the house, so I looked at several of them.   Of the older types, I found two different.  One has an electrically neutral tender, the other has a tender with a live forward truck.

On the former, the motor is not in securely.  It wobbles and has a large amount of play.  It appears that there is a plastic plate that retains the motor more or less in place by the worm shaft.   The locomotive has internal gearing at the motor and external at the drivers.  All of the drivers have gears.   Try as I might, I could not get the worm to disengage cleanly from the main idler gear.   To be sure, I did get some tenuous meshing, but it always did mesh.   If yours is of the former type, I wonder if the frame is warped or if the center hole on the idler gear is fatigued to the point that it will not turn properly on its shaft.    While many pot metal frames of that era did have zirmac fatigue and warp, break or crumble, this problem happened mostly on Rivarossi power.   I can not recall ever hearing of that problem on B-mann power.  B-mann power of that era had its problems, but metal discombobulation was not one that I can recall, at least.

If you have the latter, it has a forward truck on the tender that is live, has white plastic internal gears and no external gears.  All axles are geared.   There is a screw that holds down the motor.  If this screw is loose, missing, or if the threads are fatigued to the point that the screw will not tighten properly, the worm gear on the motor will disengage from the idler gear.  Another problem with these white plastic gears is that they crack.   If that has happened, it will appear that the motor is not engaging, but that is not the case.   The geared axles will not turn because the gears are cracked.

On the latter, you could try to buy one of these from a junk pile and cannibalise it for the parts that you need.   If you have the former, you might not be able to repair it.

B-mann has issued an upgraded version of this one.  It has a split metal frame and markedly improved runnability.  Its one weakness is that live forward tender truck that B-mann retained from the last cardboard box issue of the
USRA 0-6-0.  It is designed in such a way that it creates a tremendous amount of drag on the locomotive.  If you will buy a SPECTRUM slopeback tender or USRA short tender and swap out the stock tender for the SPECTRUM, it will render a very nicely running and pulling locomotive.  The upgrade is not difficult.   Take a peak at Spookshow's website.  He explains how to do the upgrade.   The newest versions of these come in a plastic box, so if you decide to buy a new one, be sure to get it in the plastic box, not the cardboard.

[Dgun]

My issue is of the screw hold down type. Haven't tried re-threading. Did try a longer screw but it bottomed out on the motor frame. On some of the engines it looks like someone tried a new motor and it didn't quite fit. I can seat the worm but as soon as power is applied the worm kicks out of engagement.

[brokemoto]

Introduction of an alien motor could cause the problems that you describe.   Whoever introduced the replacement motor must not have done a thorough test fit or devised a method to fasten the thing securely to the frame.   Some people have used glue, but I would shy from that, as at some point, it will become necessary to remove the motor to replace brushes, or, even, replace the motor.   On the older USRA 0-6-0, this might not be that big a deal, as, when the motor finally does wear out, you might be better off buying a newer version of this and doing the SPECTRUM tender upgrade.

At some point, I would expect that B-mann will issue this one with a factory decoder, as it is doing with all of its newer Standard Line products.   At that point, it will be necessary to upgrade the tender in order for the DCC to funtion properly.

Take a peak at the screw and see if the threads are fatigued.   I would expect that the screw would have fatigued threads before the hole in the bottom of the motor frame would have the same. 

If you will let me know in a PM what you need, I will see if I can find it for you.

[Dgun]

I will run a quick inventory and let you know. Thanks.