gear mesh problems with Model Power 4-6-2 steamer

[Loren Perry]

My Model Power 4-6-2 steam locomotive needed some electrical wiring repairs inside the driver axle cover plate and I was successful in completing them.

But when I reassembled the engine (and subsequently did so two more times with increasing levels of care and diligence), the gears began skipping like the teeth weren't fully meshed.

I Eventually tracked it down to some vertical play in the center axle which has one of the large black plastic spur gears. The chassis has a gear tower similar to an N-scale diesel which contains a train of gears that connect all three axles to the worm inside the die cast boiler. For some reason, a little excess freeplay (slop) has been introduced to the axles and I'm at a loss as to how to correct it seeing as there are no visible adjustments available. I have checked carefully under strong magnification for obstructions or pinched wires but no joy.

Anyone out there have any experience with this type of problem?

[peteski]

Are you sure that it is the axles that have the extra play and not the worm meshing with the work gear?  That is usually the problem area.

If it really is a problem with the driver axles, is the bottom gear cover fully seated onto the frame?  Can you fee the excess vertical play in the driver axles?  For the gears not to mesh there would have to be quite a bit of up/down play in the driver axles.  Like you said, the double-gear worm gear is fixed in the frame with no way to get it out of alignment.

[mmagliaro]

Model Power engines are extremely fussy about the tightness of that gear cover plate on the bottom.
I remember having this exact problem with one, although I can't remember if it was a 4-6-2.

There are several screws holding that gear cover on, and there is one very tiny screw in toward the center of the cover.
Beware that one.

As the engine is flipped on its back, if all those drivers aren't firmly DOWN, and then the cover plate snug at every screw, this gear skipping problem appears.  It doesn't take much, either.  In my case, that tiny screw was just a little loose and you'd never know anything was wrong from looking at the drivers or the cover.  I always wondered why they bothered with that one extra tiny screw.   Then this happened and I realized why.  There must be enough flex in that cover that you have to have the extra screw to keep the gears meshed.

[Loren Perry]

Hi Pete and Max -

Yes, I'm pretty confident it's the center driver because it's a bit loose in its bearings with noticeable vertical freeplay. I narrowed down the problem to the driver gear skipping because when I hold a finger on the uppermost spur gear (Actually the "worm gear") and then try to rotate the center driver with the worm gear held stationary, the driver gear starts to skip over the next gear's teeth. All this with the boiler and its worm completely off the chassis. And yes, I believe my problem lies with that tiny center screw. It seems to be stripped and the screw's head is a very tight fit in the hole cast into the bottom cover plate. I don't think it's able to get enough purchase to bring the plate tightly enough against the frame sides, and yet the cover plate seems to be be making good contact despite this.

Recommendations, if you please?

[mmagliaro]

Shucks...  If that screw is stripped, that's big trouble.
I don't recall how much metal is in the frame around that screw hole, but my first inclination would be to drill and retap that hole for a slightly larger screw.   That also means reaming out the hole in the cover plate to accomodate the bigger screw.
If it's smaller than M1.0, then I'd try tapping it for M1.0.  If it's already M1.0, then go to M1.2 or M1.4, and so on.

Of course, all this assumes you are willing and able to drill and tap tiny holes like that and you have the tools.

Even if the cover plate appears to be all the way on, my experience with these was that it just isn't held fast against the frame firmly enough to keep the driver from pushing away, losing mesh, and skipping teeth.

That's a pretty nutty place for a screw and it's a terribly small size.  The whole thing is so out of place that my gut tells me it was a late addition to the design when they discovered the gear mesh wouldn't hold.

[u18b]

This is exactly why I sold my Model Power Pacific.

I had one that ran perfectly.

But I had a need to take it apart (don't remember why)... and I saw the shortness of those screws and how tight they had to be and finicky they were.  I knew then that other people's reports were accurate and that this was a disaster waiting to happen.

I'm holding out for Kato to make a Pacific.  Glad it scored high on their survey this summer.

[Loren Perry]

Making some progress, but not all is rosy.

I found a 00-90 screw that's longer than the stock MP screw in the center position on the cover plate and its threads are a perfect match. I can now pull the cover plate snug against the frame and the original gear-skipping problem has been eliminated. Electrical pickup is still good, too.

But now the third driver axle's spur gear refuses to stay in mesh with the others. I can align it while ensuring the quartering is dead-on and the rods are loose and functioning properly. But once power is applied and the drivers begin to turn, the third axle somehow jumps a tooth and the locomotive starts hopping with every revolution. I can see no sign of a defective gear with missing teeth, etc.

All the cover plate screws are tightened and there are no visible obstructions that are causing problems with the cover plate.

I echo the post above mine that is wishing and hoping for a Kato 4-6-2, especially if it can be had with an oil fuel Vanderbilt tender. This accursed Model Power mechanism is going to be the death of me yet.

[peteski]

But now the third driver axle's spur gear refuses to stay in mesh with the others. I can align it while ensuring the quartering is dead-on and the rods are loose and functioning properly. But once power is applied and the drivers begin to turn, the third axle somehow jumps a tooth and the locomotive starts hopping with every revolution. I can see no sign of a defective gear with missing teeth, etc.

All the cover plate screws are tightened and there are no visible obstructions that are causing problems with the cover plate.

You mention that the drivers are quartered correctly, but as I recall the axles are not keyed so the drivers can accidentally be twisted on the axle. Is it possible that even though the drivers are quarter on the axle, they are no longer in proper alignment with the gear on that axle?

[mmagliaro]

Loren,

If you remove the motor, so the wheels can rotate freely on their own, can you roll them smoothly with all the valve gear working correctly, and the gears staying in mesh?  That's the first MUST to be 100% sure the quartering is right and is in sync with the location of the gear teeth.

If the above is true, I'm running out of things to suggest unless you can post some really sharp, super-close photos.  Then I might see something and have some more ideas.  But this is now venturing into territory where I'd have to see it in my hands and fool with it to see what's going on.

[Loren Perry]

Pete and Max -

I am aware of the axle to wheel interface and yes, one of the rear drivers did indeed slip and twist on the axle, but I've since corrected it and locked it in place with CA after ensuring all six drivers are perfectly quartered and there is no binding in the rods and valve gear. It so happened that I found and corrected a problem with the crosshead guide on one side that was causing some serious binding with each revolution.

With the motor and worm disengaged, I can roll the drivers manually with no rod binding, but only for few revolutions before the third axle once again mysteriously "jumps a tooth" in its gearing. It's as though one of the hidden idler gears is excessively loose but I can't get to it easily, at least not yet.

I'm on the verge of permanently retiring this engine anyway because the gear train has always been a little too noisy for my tastes and I have never been able to figure out how to quiet it. It actually seems to be coming from the motor itself because I can still hear the sound even with the motor loose from the chassis.

By comparison, I have a second MP 4-6-2 in Santa Fe markings which I bought at the same time I acquired my S.P. version with the gear problem and the Santa Fe model has always been silent, smooth, and trouble free. I guess the problem loco must be a bit of a lemon. But it'll still make a nice piece of roundhouse scenery. Sadly, it's the only Southern Pacific 4-6-2 I have on my roster so I guess my Coast Mail is going to have to dieselize until Kato comes out with a really good Pacific, hopefully with a Vanderbilt oil tender. I should live so long.

Loren,

If you remove the motor, so the wheels can rotate freely on their own, can you roll them smoothly with all the valve gear working correctly, and the gears staying in mesh?  That's the first MUST to be 100% sure the quartering is right and is in sync with the location of the gear teeth.

If the above is true, I'm running out of things to suggest unless you can post some really sharp, super-close photos.  Then I might see something and have some more ideas.  But this is now venturing into territory where I'd have to see it in my hands and fool with it to see what's going on.

[Rasputen]

I've got one that I am working on the boiler casting.  I can see that with the long screw that goes through the trailing truck pivot and into the boiler removed, that the bottom plate wants to let the rear driver move around more.  Perhaps this screw isn't tight on yours, or the rear part of the bottom plate is not fitting properly?  The idler gear between the 2nd and 3rd driver has a pretty sloppy mesh, so I can see how it will jump a tooth if the 3rd axle is allowed to move around any more than usual.

[daniel_leavitt2000]

MP steam has got to be the worst models I have ever worked on. I recently bought a used Mogul and was not happy with the wiring. What a mistake. Vale gear that won't stay put. Driver wipers that can not stay in place. Wheels slipping on their axles. Wires literally curled around everywhere. What a disaster.

[peteski]

I dug out one of my MP 4-6-2s (brand new - never ran) to see what mine looks like.  I tested it in a cradle, upside down using a 9V battery. Ran really smooth. I was putting pressure on each driver and it still worked smoothly.  There is not much play in the driver axles.  Nice and tight (with just enough play to run well).

I then remove 3 screws retaining the gear cover and tried to make the gears skip - they wouldn't.  I then tried to lift the gear cover slightly to increase the vertical play of the axles. The cover would not budge, even with the screws removed. I then tried to pull it off and it is really stuck - it still wouldn't budge! At this point I gave up as I have too many projects on my workbench. ,So basically I couldn't induce the skipping, even with all the screws removed.