USA Trains ALCO S4 truck issue diagnostic and removal

[ARIA31]

Hello All,

I just need some help. My USAT ALCO S4 is ill !

One of the 2 trucks does not run fine anymore.
The accident happened when the loco run fast against a bumper.

To understand my concerns, it is the first time I need to investigate & repair a loco.
And I am not keen to do that. So I don't feel comfortable !

I opened the failed truck and see that the two axles can move freely.
The 2 axles gears do not show wear or damages.






The failure might be at the link between the axle gear and the endless screw of the electric motor.

I am surprised by the failure as this loco did not run so much time.
Is it possible the motor disconnect from the axles gears under a shock. ?

Thus I try to understand how the truck are designed & assembled.
My understanding is that the motor block R22-12 is hold ( pinched) by the truck mounting block R22-15 without any screw (Is that true ?).

R22-12

R221-15

Then the side frames are screwed onto the truck mounting block R22-15. (3 screws on each side)

If this right understanding the connection between the axles gears and electrical motor screw is only made by the way the motor block R22-12 is inserted/pinched in the truck mounting block R22-15 ?

In this case I don't need to procure parts. I just would have to re-assemble the complete truck. (??)

I went to the G Scale bible (Greg's web site) where I found nice tips.
But one thing is missing for me : how to remove a complete truck.
I understand that I must I remove the loco shell (or is there anothe way to remove the truck).

Any comment is welcome.
I think I am not the first with such an issue with an USAT ALCO truck, so if there is somewhere a tutorial to dismantle a truck, please let me know.

 

[Greg Elmassian]

So the motor block is held in place by the bearings at the ends of the axles... the journals.

The journals are in the 2 sideframes.

The sideframes are screwed to the "A" bracket.. your R221-15.

This way the forces of the weight of the loco are not transmitted to the gears or internal bearings in the motor blocks, a nice design that has worked for years.

I would check that you do not have the "cracked axle" problem. This allows the "half axles" to spin in the center gear "casting".

There is no issue with your gears (the gear on the motor is called the "worm", and the gear on the axle is called the "worm gear" (confusing huh?)

if there was a gear issue, your worm gear would show wear, or worn teeth.

You did not indicate what the issue is, can you describe the issue better?

Removing the motor block:

I prefer to open the shell and unplug the 2 connectors for the motor block, least chance of confusing wiring.
Dissassembly here:

S4

Greg Elmassian web site on large scale trains and garden railroads, cigars, and computers

elmassian.com

If you do not want to remove the shell, then you will have difficulty with the attached wires, not all can be disconnected without removing the shell to get to the connectors, BE CAREFUL!

2 ways to remove the motor block:

1. unscrew one sideframe and pull the block out of the other sideframe, watch the wires!!!
2. pull the sideframe away from the axle tips one at a time (the sideframe is flexible, I have done this many times)

Greg

 

[ARIA31]

Thank you Greg for your immediate answer.

The 2 axles can move freely by hand. I can turn the wheel axles without any effort.

I made the test you recommend on your web site to check if there is the "crackled axle" failure , it is not the case.

So the worm is separated from the worm gear (thank you !)
Possibly the truck mounting block is broken allowing the side frames to leave the position where the worm is linked to the worm gear

I saw the § about wiring on your web page. I did not read it as I supposed the electronic part was a DCC one !
I will bennefit from your recommendation with the 2 connectors.

To remove the truck after I remove the shell, I think I unscrew the screw located in the middle of the weight.

 

[Greg Elmassian]

OK, let's get some terms right...

there are TWO "half axles" made of metal.

each half axle has a wheel pressed on to it.

These 2 "half axle" assemblies are pressed into a plastic gear casting.

You should not be able to turn either wheel independently of the worm gear.

The gear will NOT rotate if engaged with the worm on the motor.

Right off you say the axles (which I take to mean the wheel and axle assembly turn without effort.... that means the axles are cracked.

OR

The worm gear is no longer engaged with the worm on the motor.

Your pictures look weird, I don't see the worm gear...

Lift the axles out and do this:

take a picture of the motor block with the axles out.

Using MODERATE force, see if you can turn one wheel independently of the other....

Greg

 

[ARIA31]

The failed Alco S4 truck is now opened.

I do not see any broken part.
Then I believe there is lack of grease on both worms.









Until now I don't see any broken part that might explain de gap between the worm and worm gear.
I checked once more it is not the broken axle failure case.
I cannot turn one wheel independently of the other.

I made the motor running, I did not noticed any trouble with the worms. No distortion. Fully straight.
I put back the axle worm gear. They locked directly with the worm.
I made the motor running with the truck cover in place : the truck works. (empty load however)

The mystery remains for me !
Thus I am going to re-assemble the truck and see if it works fine again.
If the failure is confirmed I will buy a new truck.

For the side frame here is a picture of the journals.







I shall clean them and lubricate them again.
What oil is recommended ?
Conductive oil ? light oil ? Graphite grease (I have some)

 

[PhilP]

It might be a trick of the camera, but the lower of the two gears (on the axles photo) appears to be worn slightly concave? - If so, this could be enough to allow that gear/axle to 'ride-up' onto the worm and jam?

If this is so, you should be able to buy just the axle with gear, which will cost you a lot less than the whole block.

PhilP

 

[Greg Elmassian]

grease for the gears, lithium based, I use plastic safe grease with moly.

The worm gear "teeth" in the center look thin, but hard to tell.

So, when the motor block is assembled, you cannot turn a wheel to make it "skip a tooth"? Please confirm.

Something does not make sense.

In post #3 you say the axles turn freely by hand... please confirm that this is when the motor block is assembled.

If this is true, and you cannot turn the wheels independently with the axle removed, you either have too much play in the "bearings" between the motor block and the axles, or you have damaged the worm gear or the worm.

So please confirm the 2 items above.

(the side journals have no bearing (no pun intended) on the axles "skipping a tooth")

Greg

 

[ARIA31]

In post #3 you say the axles turn freely by hand... please confirm that this is when the motor block is assembled.
Yes it was with the truck cover removed but with side frames in place & axles inserted in the journals

If this is true, and you cannot turn the wheels independently with the axle removed, you either have too much play in the "bearings" between the motor block and the axles, or you have damaged the worm gear or the worm.
Agree on both possibilities.
I shall investigate again the worm gear profile by cleaning totally the gear teeth .

I also investigated if the motor might go backward in the truck casing but no way.

 

[Paul M]

Looks like the normal run of things, for me anyway, you have a problem, take the offending item apart, unable to find a fault, reassemble, and the d*mn thing works fine!
Maybe it went slightly out of sync, and you've reset it.

 

[JimmyB]

Looks like the normal run of things, for me anyway, you have a problem, take the offending item apart, unable to find a fault, reassemble, and the d*mn thing works fine!
Maybe it went slightly out of sync, and you've reset it.

Very true, and strip and careful re-build can fix faults that have not been fully identified, either from wear, or often in my case of second hand items, incorrectly assembled by the previous owner

 

[ARIA31]

NO sign of wear !! looks totally new even !!

 

[Greg Elmassian]

So you cannot test for gear engagement with the cover removed, there is nothing to hold the gear in mesh.

With the cover on, it should not be possible to turn the axle, by twisting on each wheel.

It really sounds like one or more axles are loose in the gear casting, although you have confirmed that they do not.

While the worm looked a bit weird in the pictures, if it was worn, the worm gear (on the axle) would be messed up, i.e. the metal worm would have chewed up the plastic gear for sure.

I wonder if the "bearings" in the motor block are worn, allowing the gears to come out of mesh... that is about all it can be, but it is much more common that the axles turn in the gear casting.

Once the motor block is assembled, there should be very little play of the axles in the motor block.

Greg

 

[Sean.]

This is the same gear ?

 

[PhilP]

Sean, I *think* all the gears are the same, but was surprised by the number of different diameter wheels they have used..

It makes having spares 'in stock' rather expensive!


PhilP

 

[Sean.]

I was just amazed that with no lube how new the gear looked

 

[ARIA31]

Yes it is the same worm gear, one is just removed from the truck, the other one is cleaned. (the axles are in identical status)

I cleaned them to check if I can see a crack.

Coming back to the root cause of the issue : a strong schock against bumper,
I favor today that it made the 2 parts (worm gear and worm) to disconnect using some flexibilty .

 

[Greg Elmassian]

To confirm: the unit still slips or what exactly is the problem?

It's never really been clear... there is no damage to either gears, and if, taking your English literally, it "slipped a tooth", it would just go to the next tooth.

Can you please explain what the current issue is?

If you lay the loco on it's back, wheels in the air, apply power, can you cause issue by pressing in each wheel one by one?

for some reason you have to click on the YOUTUBE name in the lower right of the window to get it to play...

 

[ARIA31]

The issue is now closed.
I made the assembly of the failed truck back again.
And the loco runs fine at full speed without load and with a load of several cars. Forward & Backward

What happened ? I don't really know but I will stay with following asumption :
Coming back to the root cause of the issue : a strong schock against bumper,
I favor today that it made the 2 parts (worm gear and worm) to disconnect using some flexibilty .

Thank you very much to all who looked at this thread and particularly to Greg who help me to open the truck & to find a possible cause.

 

[Sean.]

Thanks for the follow-up !