Older Atlas SD60M driving me crazy

[daniel_leavitt2000]

I am upgrading my fleet to DCC. Since I have the engines apart, I am taking everything down to the core mechanical components, washing them in detergent  and re-lubing the mechanical parts.

After reassembly, I tested the engine and it had a terrible screech. Thinking it was the trucks, I replaced them with new parts I had on hand. This did nothing. I then pulled the trucks and tested the chassis. This still produced a screech.

My first thought was that this was the worm/shaft slipping. But the worms would not turn in my hand when holding the flywheel. The flywheels were not slipping on the motor shaft either. Thrust washers looked OK.

I pulled the worms from the frame and inspected the area. There is no apparent wear or scraping along the frame. No flash on the frame metal. Bearing blocks fit tight within the frame, but the worm shaft spins freely within the bearing blocks. Connecting the bare motor to a 9V battery does not cause any vibration or squeals that might signal a problem with a motor bearing or burned out winding.

Any ideas?

[peteski]

Did you immerse the motor in your detergent solution? I usually use Naphtha to wash/degrease my locos. You eliminated the trucks. I say lubricate the motor and worm bearings (I know you aid you lubed everything). What kind of lubricant did you use? 

[daniel_leavitt2000]

I didn't dunk the motor in any liquid. I used to do tune-ups for friends, but this engine has me totally stumped.

Labelle 108 on bearings and motor.
Labelle 102 on gears (one drop per truck)
Labelle 106 on worm gear and universals (about a grain of rice on each worm, half that inside the universal and hex coupler)
Bachmann conductive EZlube on truck needlepoint cups after being burnished with a toothpick.

The only thing I can think of is that one of the bearing blocks isn't true, causing the universals to spin off center and bind. I have a few extras as I am doing the Bearden mod on my 4 axle engines.

[tehachapifan]

You've already tried my first thought, which is to lube the motor bearings and worm bearings. That said, for real stubborn screeches, I've had to incrementally add lube to motor and worm bearings with tiny droplets on the end of a wire until it went away....keeping in mind that too much oil in the motor bearings can potentially lead to problems and might even cause a short...or so I've heard. Beyond that, one thing I've found is that (at least some) bearing blocks are not perfectly square, although they will appear so when you look at them from the sides with the holes. While I've never measured them, I believe that the inner surfaces are slightly deeper on two of the (opposing) sides. You will notice that two of the inner surfaces are smooth and the other two have a louvered appearance. I found it very helpful to make note of which of these surfaces I see facing out from the mounting fingers when I disassemble a loco, so I know how to reassemble it. This is, of course, assuming that it was assembled correctly prior to my disassembly. I suspect that, should some or all be orientated the wrong way, this could potentially cause either a misalignment of the worm and shaft and/or it will move around too much (or perhaps too little?), leading to friction and the dreaded screech. I'm not sure if the orientation is the same from one loco to the other, however.

[jagged ben]

I'm dealing with a similar problem with an FVM GP60M.  I gave up on it the other day, but I was getting down to determining if the motor screeched when totally separated from the rest of the mech.  Was starting to suspect a bent motor shaft or untrue flywheel.

[peteski]

I didn't dunk the motor in any liquid. I used to do tune-ups for friends, but this engine has me totally stumped.

Labelle 108 on bearings and motor.
Labelle 102 on gears (one drop per truck)
Labelle 106 on worm gear and universals (about a grain of rice on each worm, half that inside the universal and hex coupler)
Bachmann conductive EZlube on truck needlepoint cups after being burnished with a toothpick.

The only thing I can think of is that one of the bearing blocks isn't true, causing the universals to spin off center and bind. I have a few extras as I am doing the Bearden mod on my 4 axle engines.

I would say that is anything is off-center that would cause vibration an likely another type of a noise.  Screech is usually caused by high-rpm shaft spinning in a dry bearing.  (the gears and axles in trucks spin much slower, and you already eliminated those anyway).  So all you have left are the fastest spinning parts: worms and motor.  The screech has to be coming from those.  I know that you tried the motor out of the chassis with a 9V battery and it was ok.

You know that just the motor and worms in the chassis make the noise.  SO put the motor back in the chassis with worms removed and see if the noise is still there. If not, add one worm assembly and test again.  Then the other worm.

[daniel_leavitt2000]

Bearings.

I took another look at the engine and started testing bit by bit. The worm bearing blocks were very snug against the frame. I tried several orientations but nothing worked well. Then I filed the inside notch ever so slightly to let it slip into the frame a bit easier. That did it.

My theory is that the zinc frames oxidized ever so slightly, expanding the bearing block tabs enough to push the all plastic blocks out of shape. This in turn pinched the worm, causing it to buck.

The engine is still noisy, but not screaming or binding like it was.

[peteski]

Ah, successful troubleshooting!

[RRRover]

My screeches have usually been within the motor. The shaft bearings where the shaft exits the motor frame to be exact. A small drop of lube there will work I've found.

[LarryN]

Hello,

What I discovered with some older SD50's (same mech), is that the hexagonal couplers seem to be vibrating in the flywheel pocket. I thought for sure the motor was oil hungry-it had that exact sound.
 I have not quite figured out what to do about it, but I plan on trying a little grease on the hex pieces. The hope is that the grease will dampen out the vibrations.
I am shortening a bunch of SD50 chassis for a project (C636 chassis), and I need to shorten the little Delrin hex coupler too-this is how I stumbled on this sound while testing the chassis before cutting it up.

Larry N

[Steveruger45]

Hello,

What I discovered with some older SD50's (same mech), is that the hexagonal couplers seem to be vibrating in the flywheel pocket. I thought for sure the motor was oil hungry-it had that exact sound.
 I have not quite figured out what to do about it, but I plan on trying a little grease on the hex pieces. The hope is that the grease will dampen out the vibrations.
I am shortening a bunch of SD50 chassis for a project (C636 chassis), and I need to shorten the little Delrin hex coupler too-this is how I stumbled on this sound while testing the chassis before cutting it up.

Larry N



You could try putting a small spring on the end of the hex, between the hex and the flywheel recess.  I have done this using the spring out of a rapido  coupler.