SP daylight main drive question - bearing failure

There’s nothing wrong with the dog bone set up. I have seen one Premier steam do this, but it was the nose bearing, not the rear bearing. The issue was a tiny burr not allowing the shaft to slide in & out of the bearing on the ID. So the ID was seized to the shaft, and the back lash allowed the shaft to beat the bearing apart. I have found some models with excessive back lash. Some excessive enough to walk the bearing out of the capture. I try to set these up to around .005 ( ish )…………the worm shaft OD is 4mm, so I use selective shims to pack it up. Old Pittman motor shim washers work fine here. You can also get shims from material handlers like McMaster Carr, Kimball Midwest, etc, etc, …….if you find bearings hanging up anywhere on the shaft, I’d remove the bearings, and polish shaft ends with very fine emery cloth, or 800 grit paper. With a light oiling, the bearings should slide on & off the shaft like they’re floating. You can easily knock the dog bone coupler off the shaft end with a fine punch. This will allow you to fine polish the back the side of the shaft if you feel it’s catching. If you feel like you have a boat load of back lash, and you need to shim the heck out of it, the idea is shimming the worm’s center directly over the worm wheel’s highest point in the well. This gives you the most tooth contact……clear as mud right!??….I can do a MTH gear box 101 tutorial if you need it, …..we can do it right on this thread if so,……

BTW, your pictures did not come through….

Pat

Hi Pat - can you check your junk mail for my email?

Thanks!

Your post is hard to follow and a series of pictures would make the world of difference.  Something not right on your engine if you're constantly having bearing and gears go bad.  Besides lash, the mesh matters too and it may need to be shimmed for that also.  G

I did post a picture.  Was just like back in 2019... Bearings do float on the shaft. Don't feel any spots where they catch at.  Even the one that is about to let go, freely moves on the shaft.   

Let me know it this image displays. Was from my 2019 post. Same bearing about to fail.

From my first post when I say the bearing feels rough, I meant that when I spin it, does not spin freely / smoothly. I can feel it starting to bind up within the bearing, same time I can move the outer flange side to side.

Just trying to understand the stress point that is causing bearing to fail. Yes, it has been 5 years, but engine does not run all day every day. Sometimes months between runs. The gears are ok, worm and axle drive. No glitter in the grease. I can move the shaft very slightly in and out of the gearbox, and I "feel" the mesh is ok as well. Slight play, but not excessive, to me.

Ok on the gearbox 101. Maybe see what I am missing by your run down.

@Tugboat15 posted:

From my first post when I say the bearing feels rough, I meant that when I spin it, does not spin freely / smoothly. I can feel it starting to bind up within the bearing, same time I can move the outer flange side to side.

Just trying to understand the stress point that is causing bearing to fail. Yes, it has been 5 years, but engine does not run all day every day. Sometimes months between runs. The gears are ok, worm and axle drive. No glitter in the grease. I can move the shaft very slightly in and out of the gearbox, and I "feel" the mesh is ok as well. Slight play, but not excessive, to me.

Ok on the gearbox 101. Maybe see what I am missing by your run down.

It’s odd to have this repeated failure. I feel like this might be a capture issue. Either there is excessive backlash…..( I don’t have your model in front of me, so hard for me to judge ) and the bearing is dropping out of the capture, then being beaten to death, or the bearing is not fully seating in the capture correctly, and the lid & gasket perhaps may be distorting the bearing causing it to pop apart after screws are torqued down. ( perhaps not immediately, but after some run time ) For understanding, these are NOT sealed bearings, although they look like a sealed bearing, they can be lubed by soaking them. On the second shaft you installed, did you lube them? …….they’re supposed to be lubed from the factory, but if you got an NOS part, god only knows how long it’s been on the shelf. I never trust gear box grease to get to these bearings alone, and always soak them whenever I have a gear box apart,……not saying you didn’t, I’m just pointing out possibilities,…….

Pat

@ryoung3 posted:

Hi Pat - can you check your junk mail for my email?

Thanks!

More than likely that’s where it is, ….I’ll look!!

Pat

When I got the new one in years back, I used a micro oiler and added oil on both sides of each bearing, turned bearings to help work it down in there and added more. After the first time, just thought it was a fluke or bad batch of bearings, and I got one. I used to race rc buggies at a track. We would pop off the seals ( reduce friction) and oil soak them. I didnt go that extreme and pull the shields.  This time round, the dog bone is worn down, and even the drive cups on each end are worn. Wouldn't think plastic bone would wear out the metal cups...  Ill have to take a picture tomorrow. Hopefully the MTH gets another batch of the flywheel stock in soon.    Did the image post this time?  That is what happened the first time, and was about to happen again.

I wish I had more train buddies around me. Even where I live, would think there would be more hobby shops, but far and few. Makes me want to move up north east where trains seem to be more popular. 

On the backlash part. Where exactly are you thinking of? The bearings have the brass shim between it and the worm gear. Snug fit into the lower housing. My only guess right now, maybe the bolts that hold down the top cover/plate are putting this bearing in a slight pinch, making system work harder, and not allowing internals of bearing to move freely. Something I need to look at.

The backlash is determined by the amount of rocking front to back the worm shaft does. There should be very little. None at all would be something that needs investigating. The idea being; the bearings sit in the capture. The backlash shouldn’t be so great that the bearing could spit out of the capture.

Pat

What’s odd about your failure is when the locomotive is running in forward, which is the most common direction, all of the worm shaft’s load is on the front bearing and sleeve shim. To have that rear bearing come apart in short order like yours, suggests an issue with the way it is captured. Further looking at the pictures you’ve posted of the first failure, what is going on with the spot I’ve circled on the cover gasket? …is this an indentation of the gasket? If so, it would suggest an improper seating of the rear bearing, thus the bearing would be under too much pressure when the lid is tightened down. There should be only a very very slight witness mark on the gasket itself. Also, the two bearing ends, ( the flanged portion ) should sit INSIDE the gasket’s rectangular opening. If you can, clean off all the grease from the gear box, and all the related parts, and let’s see some clear pictures. ……

Pat

Spur gears transmit only rotary motion.  Worm gears transmit rotary and lateral motion and give more problems like with the bearing on each end.

Charlie

This time when I pulled it apart, I didn't see the imprint in the gasket as you circled. As I ordered new parts, and didn't want parts to jump off the table while I'm away at work, I put it back together for the time. I do want to say where the rear bearing seats as I'm sitting here thinking, was a little struggle to get the top plate in proper place. It did not drop into place on the bad bearing side. So maybe it does need a shim. When I get the new parts in, and open it back up, ill take some detailed pictures.

Thanks for all the help

@Tugboat15 posted:

This time when I pulled it apart, I didn't see the imprint in the gasket as you circled. As I ordered new parts, and didn't want parts to jump off the table while I'm away at work, I put it back together for the time. I do want to say where the rear bearing seats as I'm sitting here thinking, was a little struggle to get the top plate in proper place. It did not drop into place on the bad bearing side. So maybe it does need a shim. When I get the new parts in, and open it back up, ill take some detailed pictures.

Thanks for all the help

Before you install the new parts, test seat the old front bearing in the the rear gear box bearing capture. Just use the bearing itself, without the worm shaft, to test fit how that bearing seats in the capture. The flange on the inside, should be against the cradle, and the bearing portion in the capture, seated all the way down. Test fit the gasket over the bearing. The gasket should cover the bearing, but leave the flange revealed, and the screw holes should line up nicely. The gasket should sit flat on the gear box top, with no gap between it and the gear box top.  If you have to force the bearing into the capture, something isn’t right. It should be a snug slip fit. Look at the capture for burs, or anything that looks different from the front bearing’s capture. Test the front capture and feel for a difference. Perhaps a piece of flashing from the casting process is jamming/distorting that rear bearing when installed. If you find the rear capture really tight, you could polish that capture with a fine grit drum sander on a dremel tool. I would stick a small piece of scrap tin or similar over the gear, to protect it from being nicked by any power tools. Sneak up on this, use the front bearing capture as a guide for the snug slip fit as it’s not having self destruct issues……

Pat

Bingo.  I think Pat nailed the cause of this problem, which is "clamping" of the rear bearing in an inappropriate position.

While you're in there... How is the alignment between the motor shaft and the worm shaft?  I have a first-generation MTH Premier Reading T1 (20-3130-1) that has TERRIBLE shaft alignment from the factory.  The shell and I believe the chassis were both new tooling circa 2003-2004, what were they thinking?  (I never could determine whether they improved the alignment in subsequent releases.)

Because of space constraints in the loco it wasn't readily possible to change the angle of the motor.  It ran ok, but sometimes the loco would bind up a little going into reverse.  A lot of it was masked by speed control but there was a definite hesitation and surging.  I scrutinized it with the shell off, and the dogbone was putting stress on the worm shaft coupling because the rear thrust bearing was rigidly clamped in place.  Possibly a dimensional error in manufacturing?  I JUDICIOUSLY filed a little of the U-shaped groove in the casting so that the rear thrust bearing was a nice slip fit, and not rigidly clamped in place when the gasket was tightened down.  You can still see the dogbone shaft wobbling around, but the hesitation and surging are gone.

If you elect to take this approach, work slowly and keep testing the fit.  Because if you remove too much from that U-shaped groove, you'll make the operation worse.  Then you'll be in the market for a whole new chassis!  Also be sure to vacuum or swab out any filings.

If you get the fit of that rear bearing correct, and make the shaft alignment as good as it can be, I guarantee that you won't have this problem again.  As Pat said, removing the coupling from the end of the worm shaft to replace the rear bearing isn't a hard job, so you don't need to buy the whole shaft, just a new bearing.  Please report back and let us know what you found out.