Atlas SD50 U-joint

[Chris1274]

I have an older Atlas SD50 (two in fact) that's pretty noisy. I thought lubricating the bearing blocks might help, but in going about doing so I noticed that the universal doesn't make it all the way into the fly wheel, as you can see in this picture:

I'm not sure of this is causing any problems, but it just doesn't seem kosher to me. The U-joint seems like it should be at least 2 or 3mm longer than it is. Has anyone else noticed something similar on their locos, and is there anything that can be done to fix it? I'm wondering if I can shift the worm gear on the worm shaft a bit, which would have the effect of pushing the universal a little closer to the fly wheel, but then the worm shaft wouldn't extend all the way into the outer bearing block. Also, the worm gear is on there pretty tight and I'm not even sure if it can be moved.

[tehachapifan]

Been a while since I've had one apart and can't recall if the motor/flywheels are asymmetrical or if the U-joints are different lengths on each end, but could the motor possibly be in backwards? Seems the frame cutout for the flywheel also extends quite a bit past the flywheel too.

[Chris1274]

No, the motor's not backwards. I also checked the U-joints and they're the same length. Here's a shot of the whole assembly:

There does seem to be some kind of asymmetry, as the rear universal (right side) seems inserted a bit further into the flywheel than does the front one.

[nkalanaga]

It looks like the difference is that the left flywheel is pushed further onto the motor shaft. 

[kiwi_bnsf]

Hi there,

I have had a lot of experience with the Atlas SD50 / SD60 mechanism and it is possible to solve the issue with the universal having too much "slop" by moving the ball joints on the worm shafts inwards towards the motor.

You can adjust the position of the ball joints on the ends of each of the worm shafts by twisting them and pulling hard inwards (with the shafts removed from the frame, and with the universal shafts removed). I usually just twist until they come off altogether, and then re-attach them onto the shaft with the minimum of shaft utilised to secure them (so to speak  )

It should be noted that the total "slop" or "play" in the drive train is the sum of the slop in each of the worm shafts. It may look as if the drive train issues can't be solved, but you just need to adjust both of the ball joints, and the play will disappear altogether (and in fact you can easily bind up the drive train if you do it too much).

Don't pay too much attention to the fact that one end of the drive train looks sloppy, and the other looks tight, because this changes as soon as the motor torques up under power (the slop is evened out). The key is that the total slop needs to be just enough to keep everything running free, but not enough to allow the shafts to rattle too much.

Please also note that the drive train slop will change once the frame is back together and tightened up. I'd recommend seeing if you can get it quiet without the trucks installed (you can simply rest the frame on the track and the frame halves will pickup power).


In case I'm not explaining myself, the following edited version of your photo shows where the slop can be reduced…




Hope this helps - be sure to post if you make progress / need more help.

Cheers

Tim Benson

[davefoxx]

I would add that the bearing blocks don't look like they're installed correctly.  It's hard to tell from your photo, but you may have at least one (the far left end) turned ninety degrees.  The bearing blocks are not perfectly square, and this could be a source of noise.  Unfortunately, because it has that universal in there, you cannot Beardenize the Atlas SD50/60 model, i.e., bearing block removal.

Hope this helps,
DFF

[bman]

I've my fair share of the SD 50/60/60M's and from looking at your photo, the left flywheel looks to be pushed into the motor shaft more than the right. 
Kiwi's advice should help.  I'm not sure if you can move the flywheel back towards the end of the motor shaft or not.  I've never tried that.

[Chris1274]

I tried Tim Benson's suggestion and here's the result:

I couldn't pull the ball joint any further outward than that, but I still think it's an improvement. The universal now extends into the flywheel about the same amount as the other one does.

I would add that the bearing blocks don't look like they're installed correctly.  It's hard to tell from your photo, but you may have at least one (the far left end) turned ninety degrees.

I think that's an optical illusion. I double checked and they're all installed in the same way. I also tried rotating them 90 degrees but they wouldn't fit that way.

I'm not sure if you can move the flywheel back towards the end of the motor shaft or not.  I've never tried that.

It can't be done by hand, at any rate. I just tried on a spare motor and the flywheel wouldn't budge.

[Chris1274]

The locomotive is running much more smoothly and quietly now. Thanks for your help guys.

-Chris

[davefoxx]

Chris,

Since you've gotten it to run smoothly, leave it alone.  But, in the future, if you're ever "under the hood" again, I noticed that the worm at the left has no thrust washers at the left end.  You could eliminate some further slop in the drivetrain by inserting the necessary amount of washers.

Oh, and I'm glad you confirmed that the bearing blocks were all in correctly.  Sorry for any confusion, but I think you're right, there was an optical illusion in the picture.

DFF

[Chris1274]

I noticed that the worm at the left has no thrust washers at the left end.  You could eliminate some further slop in the drivetrain by inserting the necessary amount of washers.
DFF

Good eye Dave, thanks for pointing that out. I'll have to get some of those washers from Atlas.

[trainforfun]

Hi there,

I have had a lot of experience with the Atlas SD50 / SD60 mechanism and it is possible to solve the issue with the universal having too much "slop" by moving the ball joints on the worm shafts inwards towards the motor.

You can adjust the position of the ball joints on the ends of each of the worm shafts by twisting them and pulling hard inwards (with the shafts removed from the frame, and with the universal shafts removed). I usually just twist until they come off altogether, and then re-attach them onto the shaft with the minimum of shaft utilised to secure them (so to speak  )

It should be noted that the total "slop" or "play" in the drive train is the sum of the slop in each of the worm shafts. It may look as if the drive train issues can't be solved, but you just need to adjust both of the ball joints, and the play will disappear altogether (and in fact you can easily bind up the drive train if you do it too much).

Don't pay too much attention to the fact that one end of the drive train looks sloppy, and the other looks tight, because this changes as soon as the motor torques up under power (the slop is evened out). The key is that the total slop needs to be just enough to keep everything running free, but not enough to allow the shafts to rattle too much.

Please also note that the drive train slop will change once the frame is back together and tightened up. I'd recommend seeing if you can get it quiet without the trucks installed (you can simply rest the frame on the track and the frame halves will pickup power).


In case I'm not explaining myself, the following edited version of your photo shows where the slop can be reduced…




Hope this helps - be sure to post if you make progress / need more help.

Cheers

Tim Benson

Thanks Tim for your hint !!!!

[kiwi_bnsf]

I'm glad the fix worked for you as well 

As an aside, none of my SD50 or SD60 mechanisms came with thrust washers on the outer sides of the worms - so I think that is by design. I only add thrust washers on a case-by-case basis if there is significant "buzzing" at the worm, although in my experience noise in the worms is often caused by loose bearing blocks or slop in the drive train.

The Atlas SD50/SD60 mechanism suffers from a lot of issues and can be hard to get working smoothly. I've had good experience swapping out the Atlas wheel sets and replacing them with Kato 932090 wheels. The Kato wheels have longer points on the ends of the axles, and this reduces the floating axle problem that the Atlas HT-C trucks suffer from. They also look a lot nicer…







[Full credit to Ron Beardon for the original Kato wheel set replacement idea]

Cheers

[ryan_wilkerson]

I agree with Tim on the Kato wheel replacement. Looks much better and I like how it performs. Tim actually typed up a nice description of the process in an email to me about two years ago (thanks!). Since then, I've upgraded at least a dozen units (Atlas SD50 / SD60 and Intermountain SD40T-2, SD45T-2 and SD45-2). All look way better and it cost just a bit more per axle as upgrading a freight car to metal wheels.

Glad you got it quieted down!

[GN63]

What Kato wheelsets did you use, with gears?  I agree - they do look much better.