Bachmann "Yard Boss" 0-6-0 Shell Attatchment Problem

[Puddintan3]

I recently bought the Bachmann N scale "Yard Boss" set with the 0-6-0 AT&SF steam locomotive. I was having some issues with rough operation until I found a message from February 2010 that discussed the same issue. I followed the directions that included inspecting the armature for carbon caking. Sure enough, cleaning the armature did wonders! It now starts smoothly and runs well at slow speeds, both forward and reverse.

Now that I have completed the work, I am having trouble getting the shell to properly attach to the body. The directions had said to remove the single screw in the sand dome to detach the shell. Now I cannot get the shell positioned to let the screw thread into the tapped metal hole. If I take the screw by itself, it will take the threads and tighten. However, it appears the tolerance is so close that when the shell is on, the screw cannot reach the point where it tightens. I have looked carefully to ensure the shell is sitting tightly atop the body. It seems somehow either the screw is a bit too short, has bad threads, or the tapped hole has bad threads.

My essential question is, what will fix this problem?

[brokemoto]

My initial thought would be that the screw, the threads in the chassis or both, are stripped.  If not totally stripped, there may be a flaw somewhere.

However, you do state that the screw will take the threads and tighten.  I am assuming that it will tighten fully.

The next thing to do is make sure that the shell is seated properly on the chassis.  To replace it on the chassis, you must have it slightly forward.  As you tilt the cab end down onto the chassis, you slide it backward and seat it correctly.  Be sure that the screw goes into the hole straight.  DO NOT try to turn it super tight-that WILL strip it or its hole, if one, or both, are not already stripped.

If you want a real improvement in performance, especially pulling power, buy a SPECTRUM tender; either the slope back or USRA short.  The slope back is incorrect for the prototype, a USRA 0-6-0.   The USRA short, or switcher tender, is correct.  According to someone who should know, none of the copies, even, had the slope back.  Some roads did modify the USRA short tender, or even changed the tender to a so-called "wide vision" tender.  This involved the narrowing of the coal bunker by moving the coal boards inward.  

If you will go to Spookshow's website, he explains the modifications necessary to swap the stock tender for a SPECTRUM.  He states that no modifiactions are necessary if you use the slopeback (at least he did the last time that I read it).  I have found that a modification to the slopeback similar to that which he describes for the USRA short makes the whole thing operate better.  If you have a Dremel tool and a little care and patience, the modification is not difficult.

[Puddintan3]

Thanks for your reply. I also suspect some stripping has occurred, which I now wonder how to correct. I'm thinking that even though it will thread without the shell, the screw can't reach the good threads in the body with the shell on. I have tried positioning the shell as you suggest, but I'll give it another try.

If this fails, what could I do to the body in order to re-tap the threads? Do you have any idea what the size of the screw is? Would a medium strength glue applied to the body hole work, allowing you to still turn it out?

[Mike C]

 Possibly using a rubber band to secure the body,  and use a small amount of epoxy in the hole ? and of course put the screw in the hole while the epoxy sets. ?

[Puddintan3]

I was thinking along that line. The thing that concerns me is that excess glue might get between the body and shell, permanently holding them together. I'm trying to do this so that I can still get the screw out and separate the body from the shell in case repairs or maintenance is needed. I fear epoxy is too strong. What would be the best is a sort of soft metallic "putty" that could be put in the hole, put the screw in, let it harden, the back the screw out leaving new threads.

It concerns me that the metal in the hole is so weak it is easily stripped. I always turn screws and nuts a 1/4 to 1/2 turn in reverse to allow the threads to align to avoid cross-threading. I also use small drivers and turn them gently to ensure the threads are engaged before I tighten down.

[James in FL]

A slightly longer screw would be my first thought as you state you have good threads, just can't reach them.
Another fix would require complete disassembly to the bare frame halves.
You could then fill the hole with silver solder, re-drill and tap.
I have had success threading JB weld, again fill the hole and drill and tap.

Can you accurately measure the diameter of the screw and the length?

[Puddintan3]

James - I do have an electronic micrometer. I'll have to get it from my shop.

Just guessing, I imagine only a few millimeters longer screw could do the job.

This locomotive is new, and I'd hate to disassemble it down to the halves. I haven't had a chance to check with Bachmann directly yet, but I posted here in the meantime to see if a simple remedy was available.

Thanks for the reply!