MTH RailKing 4-6-2 gear skip

Any durable shim material is "permanent", if it stays in place (use CA or the like) and doesn't interfere with anything else. You have, indeed, "fixed" it. Nothing else to do. Shimming, even in original manufacturing, is a common procedure, and some machines are designed to be shimmed as wear occurs. It's legit.

I had a noisy Weaver brass Dreyfuss Hudson. Looked at the motor and it was, indeed, sagging on the motor mount. U-joint was noisy from the angle. All screws were tight. I shimmed/tested,etc a few times using styrene. It is fine. I glued the styrene shim in place. 

Fix that shim in place and move on.

Occasionally this has to be done.  PW lionel used shim washers.  If it runs fine now, your good to go.  G

Thanks guys for your help.  I like to work on trains and get a lot of good information from this forum which encourages me to keep on going.  

Good job LUV.  But which version of the Blue Comet is this (RailKing or Bantam), what is the product number?  And where exactly did you put the shim?  Thanks.

Is there any possibility that the worm gear on the motor is not straight or perfectly concentric with the motor shaft?

Ted, this is a RailKing model 30-1172-1.  I slid the shim into the center of the bottom between the motor and bracket.  When a load is placed on the gears, the back of the motor would tend to rock downward letting the gears move too far apart causing them to skip.  As Roy asks - be sure to check the worm and ring gears to make sure they are all correct.  It does not take much misalignment or wear for these gears to skip or slip.  But in my case, if you look closely in the photo above, you can see a little gap towards the top of the motor / bracket assembly.  This same gap is also at the bottom.  So this was letting the motor flex or move letting the gears skip under a load (even just a tiny load).  So I took the three bolts out of the bracket to remove the bracket / motor assembly.  Then loosened the two mounting bolts on the motor just enough to slide in my "shim".  All that is needed is to firm up the assembly.  By putting the shim in at the bottom, the motor can is held solid keeping the gears at the correct position so they don't skip. Be careful not to make the gears fit too tight.  There has to still be a little clearance for them to operate properly and not bind.  That's why it took me a couple tries to find a "happy spot".  The best way I could check was by turning the motor's flywheel when I had the motor / bracket assembly remounted on the chassis.  It needs to turn freely and should be able to feel a tad bit of play between the gears.  Hope this helps you.

Now I understand what you did, and yes that seems like a good fix.  Please bear with me for a couple more questions though...  Per the catalogue, 30-1172-1 was originally equipped with Protosound 2.0 or LocoSounds.  Did you remove the tach tape and reader?  That flywheel looks mighty big!  Also, is the motor geared to the center pair of driving wheels, or the LAST pair of driving wheels?  Thanks!

Ok,  Let me reboot, now that I see and understand what you did better.  Ted, center and this looks like a PS-1 version.

On the motor did you check the 2 screws that mount the motor to the motor mount bracket?  If they were loose, that could be your issue.  IF not loose, did the bottom of the can motor have a slight distortion?  I have not run into that area being bad on motors unless the motor can got a twist in it.  That can be straightened with a little tap.  Otherwise loose motor mount screws to the can motor is the most likely issue.  G.

I have one that did the same thing. Sent it to MTH to get it fixed and they have had it for over a year.

Not happy...

Ted, my engine is a Protosounds 2.0 and is geared to the rear axle.  I did not remove the tach tape and reader.  I only unbolted the electrical wires on the rear of the chassis (tender plug, smoke unit switch, and fire box light).  That gave me enough room to work with the motor and bracket.  Might have been easier to unhook more, but I didn't.  Your right.  That is a big flywheel.  Before I took anything apart, I turned the flywheel by hand thus turning the axles / wheels.  A with just a little resistance placed on the wheels, I could watch the motor flex and the gear would skip.  I checked for the trouble points as G states above, but could not detect anything unusual. I thought about trying to tap the can motor face to try and flatten the surface.  But I did not want to cause damage to the motor.  It spins freely, smoothly, and quietly.  So that is why I went with the shim on the bottom.

Steve,  Sorry to hear that your engine has been gone for over a year.  I have seen a lot of satisfaction on this forum with MTH service. And then some with your same issue.  Seems odd to have such inconsistency.  Just to share with you, I had an engine at an "Authorized MTH Dealer".  It too sat there for about three months.  I got the same answer several times when I called - "It's next in line.  Just finishing a warranty repair on another engine and that has to come first."  Well somehow my engine never made it to the front of the line.  This being the first MTH that any of us on our family layout has had trouble with, I was leery about working on it.  I have tinkered with trains since I was about ten years old and have kept them going.  (Hmm.  Guess that makes it about 30 years that I've been modeling O gauge and working on them.)  But these newer ones are a little intimidating.  There's a lot of electronics in there.  But I could wait no longer to get this engine up and running.  So the dealer shipped it back to me.  And with the help and encouragement of this forum, I was able to get her back up and running.  Just in time for the Christmas Holidays.  Hopefully you can get yours back soon.  The old saying goes "The squeaky wheel gets the grease".  In other words, a little pestering will sometimes get results.  But then again, too much will cause the wrong results.  Good luck.

Sorry G, you are correct on your statements from the picture shown.  I must have loaded the wrong one.  My bad.

I had one that the chassis got dropped and bent something, it wasn't obvious what it was.  A shim was the solution, so that's what it got.  AFAIK, it's still running that way.

LUUUUUV Trains posted:

Sorry G, you are correct on your statements from the picture shown.  I must have loaded the wrong one.  My bad.

It happens:-)  G