Screeching Locos?

[CBQ Fan]

I have three atlas SD24’s that all screech at about the same speed. However if I run them without the shell no screech. Any ideas on what would cause this? 

[mmagliaro]

You're sure it's a "screetch"? I would have expected the motor armature rubbing on the shell somewhere, but that would not cause a "screetch", which I think of as the sound when a motor bearing runs dry.

How old are the engines, and have you EVER put a drop of oil on each motor bearing?  If not, I would try that... ONE DROP ONLY.
Even though it doesn't do it with the shell off,  if they have never been oiled in years, there is an off chance that the shell puts a little pressure on the motor housing, and maybe it's just enough to put a little pressure on the motor shaft in its bearing.
If one drop doesn't do anything, forget this blind alley and we'll have to diagnose further.   Adding lots of oil just accumulates more dirt and junk and can ruin a motor.  So I stress..  ONE drop on each bearing.

[Steveruger45]

Yes as above, but it could also be the drive universals slipping.  The donut part of the universal mounted on the motor shaft often splits.

[CBQ Fan]

My initial reaction to the sound is metal on metal but it is only present at a very narrow portion of the speed band.  I would think that if it is metal on metal it would nut go away at higher speeds. I did put a small amount of lubrication on the bearing blocks.  They are original runs so they have been around awhile.

[Steveruger45]

Hi Brian, I have had the same issue but on some older Kato locos.  And yes, only at certain speed bands.  It was the motor bearings in all those cases.  Fixing it was a long laborious task of one drop on oil on each bearing then running it a while then “rinse and repeat” over and over again.
Out of the four affected locos I have, three were fixed this way and the other one just wouldn’t fix without changing the motor.

[CBQ Fan]

Hi Brian, I have had the same issue but on some older Kato locos.  And yes, only at certain speed bands.  It was the motor bearings in all those cases.  Fixing it was a long laborious task of one drop on oil on each bearing then running it a while then “rinse and repeat” over and over again.
Out of the four affected locos I have, three were fixed this way and the other one just wouldn’t fix without changing the motor.

So this is a bearing in the actual motor?

[Steveruger45]

So this is a bearing in the actual motor?

Yep. Both of them.  Put one drop of oil (using a bit of piano wire or similar) onto the shaft between each motor bearing and the flywheels and run for a while and repeat.

[mmagliaro]

So this is a bearing in the actual motor?

Oh yes!  Absolutely.  All the Kato and Atlas (and pretty much everything else)has a bearing on each end of the motor where the shaft comes out, and if it goes dry, it will screech like mad.  Usually, it just screeches all the time (regardless of the shell being on).
And that's why I was so adamant about "one drop".  If you put too much oil on a motor bearing, it ends up inside, gets sprayed all over the place, including on the brushes and commutator, where it collects dirt, carbon, and goo, and can start shorting the commutator sections together.

[CBQ Fan]

Oh yes!  Absolutely.  All the Kato and Atlas (and pretty much everything else)has a bearing on each end of the motor where the shaft comes out, and if it goes dry, it will screech like mad.  Usually, it just screeches all the time (regardless of the shell being on).
And that's why I was so adamant about "one drop".  If you put too much oil on a motor bearing, it ends up inside, gets sprayed all over the place, including on the brushes and commutator, where it collects dirt, carbon, and goo, and can start shorting the commutator sections together.

I tore two of them down completely and boy were nasty dirty inside. Both were eBay purchases just before I moved a couple years ago.  One seems almost as new. The second is much better but I think I may need to lube it like you suggested. There was so much gunk inside I wanted to see what simply cleaning it did.

[peteski]

If you took the mechanism apart and it is really dirty inside, then this very likely indicates that it needs to be lubricated.  I would recommend a full cleaning (in an ultrasonic cleaner if you have one), drying all the parts, and full lube job.  That way it will be almost like new. 

Lubrication includes using light oil on the fastest rotating parts (motor and worm bearings), regular weight oil on all gear axles (in the trucks), and axle bearing cups, and plastic safe grease (Like White or Moly grease from Woodland Scenics) on all the toothed gears (including worms).  Apply all the lubricants very sparingly.

[Bill H]

Apply all the lubricants very sparingly.

Emphasis on "sparingly" or you will recreate what you found in one of them...

[CBQ Fan]

If you took the mechanism apart and it is really dirty inside, then this very likely indicates that it needs to be lubricated.  I would recommend a full cleaning (in an ultrasonic cleaner if you have one), drying all the parts, and full lube job.  That way it will be almost like new. 

Lubrication includes using light oil on the fastest rotating parts (motor and worm bearings), regular weight oil on all gear axles (in the trucks), and axle bearing cups, and plastic safe grease (Like White or Moly grease from Woodland Scenics) on all the toothed gears (including worms).  Apply all the lubricants very sparingly.

I do not have an ultrasonic cleaner. All of my efforts have lead to notable improvements so I will go at it again.

[CBQ Fan]

Ok, a thorough breakdown and cleaning and light lubrication and all three are running much better.  What I cleaned out looked like a mixture of thick snot and soy sauce.

[randgust]

I have 14 kato six-axle mechanisms, and about four of them have developed the 'kato screech' and been lubed, instant fix.

The amazing part is how well it's worked and how long it's fixed the problem.    Years.

[CBQ Fan]

I just find it odd that it only makes the noise at a very specific speed range.