Railking Imperial Y6B front truck randomly derails- does this theory make any sense?

I'm not an expert but, is there any track irregularity whatsoever where the derailment occurs? Is the axle of the leading truck lubricated? Rather than buying a new spring to increase the download on the truck, it may be possible to insert a shim and reuse the original spring.

MELGAR

Melgar, Love the idea of the washer / shim.  Although nothing was obvious, I took your idea of a strange track irregularity and replaced two straight 10 inch sections of track- voila, 8 loops without a derailment.  I have eyeballed the replaced track until I am cross eyed- will need to do some measurements but those were great suggestions.  I had not had a track irregularity issue (at least one I noticed) in the past.  Now I will not take that for granted.

I put a straight edge across the three rails of the "bad" track and the middle rail was about 1/16 above the outside rails.  Apparently, either the gear box or the pickup rollers were riding up on that and in turn causing the front truck  wheels to raise and come above the rails at that point.  I still like the idea of adding a shim and will do that in a few days.  

I have used 3 of MTH's RK 2-8-8-2's (the USRA version has the same running gear as the RK Y6. so far as I know) for project locos, and all 3 had to be fixed because of the front truck. Mine would derail mostly on a switch, but it wasn't limited to that.

So, I turned it over and looked. The front truck has a large oval mounting "hole". This allows the truck to flop around at either end - essentially it can pivot around an imaginary center  - and off it goes. This was on GG track with 072 curves, BTW. And 0-100 switches.

I epoxied a washer on/over the oval hole to act as the new screw-attachment hole. Problem solved. I automatically fixed the next 2 locos as I started their projects.

The rear never seemed to have the issue - small differences in running dynamics, I guess.

I have no idea how this fix would affect the loco on smaller, "RK" curves.

I also have had this problem.  Stiffer spring didn't help.  Washer idea sounds interesting.

I have the same engine and I run on O36 superO track and switches. It runs perfect thru both. 

Most of problems with derailing is usually the track not being laid correctly. It is the most important thing to do right when building a layout. The straight edge and measuring tape should be used for a reason.

Dave

Thanks for the  suggestions and good ideas.  Interesting how these multiple factors could be issues. For sure l learned a lesson on checking track sections- (BTW, I am using Lionel traditional track.)  Although it appears most of my issue was solved by changing track, when  I get back home on Thursday, I plan to use some removable adhesive on that washere idea on the oval slot to see if that makes it more bullet proof.  I do have a remaining issue  on one lionel 071 switch.

D500 posted:

The rear never seemed to have the issue - small differences in running dynamics, I guess.

I have no idea how this fix would affect the loco on smaller, "RK" curves.

My guess is front truck is being "pushed" and has to find its way along the rails, while rear truck is "pulled".  Remember how easy it was as a kid to pull a wagon than push it and wheels seemed to wander.

rrman posted:

D500 posted:

The rear never seemed to have the issue - small differences in running dynamics, I guess.

I have no idea how this fix would affect the loco on smaller, "RK" curves.

My guess is front truck is being "pushed" and has to find its way along the rails, while rear truck is "pulled".  Remember how easy it was as a kid to pull a wagon than push it and wheels seemed to wander.

Actually I was referring to the rear truck's behavior when the loco was backing up; the stock rear seemed happy either direction. Sorry to be unclear.

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RJR: "Washer idea sounds interesting."

Not only that, but it works.

Don't have one. Is it greased so the truck can slide side to side on the frame? Some rub & may not return all the way.

thanks to all for the comments and suggestions.  things are about 80% improved.  Here is what I have done so far. 

1) all the front truck pivots and wheel bushings are lubricated.

2) I replaced one 10" section of tubular track.  the middle rail was too high.  what does that mean?  Well I figured the middle rail should only be the thickness of the insulation material high.  this section had the foot of the rail in an arched (not flat) configuration, adding maybe 1/32 to the height.  ( this has been a lesson for me in tolerances.)

3) I replaced one more section of 10" track.  Same deal on the height but this one must be extra high (I pitched the other piece of track so no chance to compare.) I can't believe I did not notice the pitting on this piece from arcing of the rollers.  Note the top part of the middle track in the picture. A number of my locos obviously did not like this one.  My guess is my MTH steamers that have that low rounded gear box with the screw to add grease (like the Y6b) actually ride up on this middle rail and the roller almost loses electrical contact- hence the arcing.  

4) I bought some shim / washers so will try that next if needed.  Want to get some run time with these replaced sections. 

BTW, I also found another issue related to that low hanging, rounded gear box.  One of my Lionel 072 switches has a high frog and it also lifted that gear box up enough to derail.   Just bought a Ross and no more issues at the 072 switch.