Atlas SD50

[u18b]

I sort of became an expert on the HT-C truck.

Whatever, the design difficulties, they tend to be focused mainly on the first run or so.  I hardly ever hear people talk about it any more.

The thread where I walk you through possible changes was referenced by Chris, but his modified thread has no photos.

That original thread is still up on the Atlas board.

Here it is:
http://forum.atlasrr.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=42265&whichpage=14&SearchTerms=axle,hop

But as you read through page 14 and 15,  notice toward the middle-bottom of 14 that I made a HUGELY important performance discovery.

The trucks are not 100% symmetrical.

The key is that the metal pick ups in the truck have a LEFT side and a RIGHT side.
The sides are identified by the MARK.



So read that thread, and see how it helps your trucks.

I predict they are not assembled properly.

[u18b]

Dave,

I was just reading through that 15 page thread at Atlas and saw that you were an active contributor.

[davefoxx]

Hi, Ron,

Yep. I was.  As I pointed out earlier, I sold my old SD50s and, when I decided to model the Seaboard System again, I repurchased replacement SD50s.  Unfortunately, that brought back some problems.  As you noted, this seems to be only from the distant past.  That's actually good news, and the Atlas SBD SD50s were released in the first run in 1999.  So, I should be able to fix this problem.  Hopefully, new trucks will fix this, and I don't have to resort to the expense of completely new mechanisms.  But, SD50s were some of the latest purchases on the real SBD, and I really want to use these model locomotives.

You pointed out the metal pickups.  You're right, they're not symmetrical.  In fact, when I was putting the trucks back together last night, it was easy to see that if I got the sides reversed the center axle would not stay parallel to the others.  So, I am certain that I have the trucks assembled properly, and they are very free rolling.

I believe that the problem is in the worm gear or its mesh with the worm.  The locomotives (both of them) run well on straight track, and one of them slows down in the curves.  The other one does, too, but only in right hand turns.  The problem lies in pressure on the worm when the trucks turn.  For some reason, it's causing excessive force that the motor cannot completely overcome, and the locomotive slows.  I would chalk it up to sharp curves, but others seem to be running on sharp curves without problem.

As I pointed out in a recent post, I discovered at least one truck has that loose worm gear problem.  I am hoping that new trucks, which I ordered today, will fix my problem.  Here's to hoping that I receive "new" trucks and not "new old stock."

DFF

[davefoxx]

Well, you're not going to believe this, but I got the bad SD50 running much more smoothly, merely by adding a thrust washer at the end of the driveline between the worm and the outer bearing.  I tried to put another at the opposite end of the locomotive, but I could feel significant drag on the driveline.  So, I pulled it out, which regrettably left a bit of slop in that worm end-to-end.  For shits and giggles, I put the locomotive on the tracks, and, "WTF?!," it ran around the layout without slowing down!

Crappy video evidence:

(Sorry, I'm not sure why the "YouTube" link here will not work to implant the video in this post.)

Interestingly, the sharpest curve on the SBD mainline is a short 11 3/8" radius curve on the passing siding adjacent to the F40PH in the video.  By the way, I also put the unit on the A&R line with its 10" minimum radius.  Not a problem.  I hope this is not a fluke, because I have torn down these locomotives several times over the last few days.  Oh, I guess I better disclose that I did try to squeeze the gear tower to tighten up the loose worm.  I'm not sure if this had any effect on the improvement.

I expect the new trucks to get here on Thursday, and I look forward to getting rid of the old trucks and their inherent problems.  I'm also hoping a thrust washer in the other SD50 will make it also run better, e.g., right-hand turns.  We'll see.  Worst-case scenario: I've got both SD50s running counter-clockwise in a back-to-back order.

DFF

[wazzou]

Interesting fix Dave.  What is it that led you to try the thrust washer?

[davefoxx]

Bryan,

Although, these six-axle locomotives cannot be Beardenized, I learned through that process on four-axle locomotives that you have to minimize the end-to-end play in the worms/driveline when removing the inner bearing.  Remembering the length of play on those worms made me realize that the SD50 worms had a lot of end-to-end play.

DFF

[davefoxx]

Well, the new trucks (approximately $30.00 shipped) were a complete waste of money.  They have the same problem of the loose worm gears on at least two of the four trucks, but even more severe was the electrical continuity problem.  No matter how much I cleaned out the metal pickup strips and the wheels, I could not get most of these trucks to run well under the SD50s.  I literally ended up with the original four trucks back under the SD50s.  I'm concerned that I got "new old stock."

So, I couldn't get the locomotives running any better with the new trucks, and, after much tinkering, I finally have them back to the level of performance they were the other night.  Unfortunately, I should have left well enough alone.  I had to take these things apart a dozen times to get the performance back.  Even swapping the trucks from one end to the other would have significant effect on how well the locomotives ran.

For now, they'll run around the layout reasonably smooth, but not nearly as well as my Atlas four axle locomotives and not even close to a Kato.  Plus, I've had to "settle" on speed matching them, because they run at slightly different speeds in forward or reverse.  So, they are running okay, but I'm not 100% satisfied.  I shouldn't complain, because at least I have them running without slowing down in the corners or acting erratic.  At least I can use them now.

I'm really tempted to buy new locomotives.  MBK has Atlas SD60s on sale for $74.99 each.  A simple shell swap would allow me to use the SBD shells on 2013 mechanisms.  Hopefully, Atlas has made modifications to the SD50/60 line, so my problems don't recur.

DFF

[johnh35]

Shimming of the worm can cause you grief. As the truck pivots, it needs "slop" in the worm to allow fore and aft movement. I fixed an Atlas C628 for a gentleman who had a similar problem by removing all worm shims. Less is better than more. YMMV

[davefoxx]

Shimming of the worm can cause you grief. As the truck pivots, it needs "slop" in the worm to allow fore and aft movement. I fixed an Atlas C628 for a gentleman who had a similar problem by removing all worm shims. Less is better than more. YMMV

John,

The next time that I tear these units apart, I'll try that as an experiment.  I can say that I was careful to ensure that the additional washer didn't make the worm too tight.  I was only able to put one thrust washer in one locomotive.  The other locomotive was too tight when I tried, so I took the washer back out.

DFF

[jbcz]

I had this problem years ago with Atlas GP40 and GP40-2 locomotives.  The spur gear that meshes with the worm has straight teeth.  On certain curves it will bind with the worm.  I found a simple solution for the GP40s.  I bought Kato spur gears from the GP30/GP35.  Those gears are angled to mesh with the worms.  When I installed those gears, the locos would crawl around corners with no problem.  This was only a problem on one 9.75" curve on a branch line.

[crrcoal]

Does anyone know is this issue still exists with the newer 2013 SD60's?
Or better yet what years are the affected engines? I'm looking at a 2006 version but will pass on the deal if it has the same headaches Dave had with his unit.
Thank you!

[conrailthomas519]

I have 8 units available for sale... if interested check out the post under the trading posts here on therailwire titled Updated locomotives for sale PRR, Seaboard, Conrail

[randgust]

My often-photographed FP45 actually has an Atlas SD50 mech under that Lima shell.  So I know all about the SD50 mechanism.

Mine definitely had worm binding when I first got it; basically it got run so hard and so long that I'm assuming it polished up the gear teeth on its own.   Very annoying, more or less the way you describe it.   Oh, and on full slip mine clicks a bit, but it rarely slips with all the extra weight it put in it as an FP45.

One rather non-destructive test you can do is take either thin styrene (.005, or .010) and put some shims on the frame where the truck pivots; don't try to shim the worm bearings  in the frame, shim the trucks down just a hair.   It doesn't take much.   If it starts to 'jump teeth' you've overdone it.  If it actually does work you can substitute shim brass or just change out the styrene shims periodically.  I hold mine on with just a touch of Goo.  Because the pickup ears do all the electrical pickup this doesn't impact anything at all, and you can pull them right off anyway if it doesn't actually improve it.   No damage to the frame that can't be immediately undone if it either makes it worse or doesn't make any difference.   You want that thin shim so that it's right on top of here (wow, the old Atlas forum is getting a workout!)
http://forum.atlasrr.com/forum/data/CSX%20Robert/20078249350_atlas%20truck2.jpg

I agree that it's basically because from what I can see (from top angle) is that the Atlas gear teeth that mesh the worm aren't angled.  So whatever you do - thin that gear, use a different gear, run the wheels off it to wear the teeth, or even lower the truck a bit, all increases that tolerance and prevents binding just a bit.

[crrcoal]

I'd love to add a couple to the roster but I don't want to deal with the headaches. At 80 a pop I'm not so sure it's worth chancing. 

[sizemore]

Have you tried taking out the center wheel and running a 4 wheeled truck, just as an experiment? That might give a better idea of what's going on in the truck.

With newer steam locomotives I find polishing the gears helps a lot for a binding mechanism. With old Rivarossi Locos you'd pack them with toothpaste and run the snot out of them. Followed by a thorough cleaning a light lube would make them much better runners. Might consider the same here.

The S.