USA TRAINS F3 replacement motors

DVS4G

DVS4G

RR Dave
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I bought some replacement motors for a USA Trains F3 and am wondering about the screws sticking out the ends of the bricks. The old motors had the same screws, but they were screwed all the way in. The screws on the replacement bricks are only screwed in a little ways. I disassembled the brick and found that the screw goes in toward the end on the worm gear on the motor shaft. When screwed all the way in, it just misses the end of the gear. So I'm puzzled about why they are not screwed all the way in like the ones on the old bricks. Does anyone know what they are really for?
 
They hold (or should I say held as it appears you may have lost them on disassembly) a thrust bearing in place I imagine the screw is used to ensure that the tension on them is correct.
 
The screws are for the end float of the motor armature. They are actually screwed into small plastic blocks that are set into the motor block casing.
Screw them all the way in leaving just enough so they won't cause the armature to drag. They will help reduce the motor bearings having to take up all the end float which will increase with wear.
Too much end float on a single start worm can result in surging down grades as the loaded worm gear takes up the end float intermittently while the worm shaft is progressing through it.

USA_MotorBlockF3_00_5784.JPG
 
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By the way, that is NOT a USA Trains motor block for the F3 or any of their diesels I know of.

The adjustment screws on the block shown are as reported.

The picture below is a USA Trains F3 motor block, with NO adjusters: (never had them to my knowledge for the last 20 years)
coveroff.jpg


As opposed to an Aristo-Craft 2 axle motor block used in the FA:
(there are about 5 versions of Aristo 2 axle Diesel motor blocks, with zero, one, or 2 adjusters)
bb_block.jpg
 
Greg Elmassian said:
By the way, that is NOT a USA Trains motor block for the F3 or any of their diesels I know of.
The adjustment screws on the block shown are as reported.
The picture below is a USA Trains F3 motor block, with NO adjusters: (never had them to my knowledge for the last 20 years)
Click to expand...

Greg. I bought my motor block as a spare from eBay and it is exactly the same as the motor blocks on the USA Trains GP38 which I have.
Your picture looks exactly the same as my motor block but taken from the bottom rather than the top. Are you sure you don't have a screw loose? :p

Here is a picture of a USA Trains F3 from a well known large scale enthusiast's website. ;) You can see the screw in the end of the motor block.
F3 disassembly

Gregs_F3_Bottom.jpg
 
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Well now, didn't mean to start a war here. It seems you are both correct. And yes, one picture is from the top and the other is from the bottom. I got mine from Only Trains. I will attach the picture from their catalogue.
Only Trains Replacement Motors.JPG
 
I also had a moment when I was trying to figure out just exactly what the difference was between an F3 and a F7. Hard to tell the difference in these G Scale models?
 
Thanks for the link to disassembly, Paradise. Very helpful. Here are more pictures of what I am working with.
First Picture, the old motor where the screws are all the way in.
Old Motor - Screws in.jpg
 
Next we have the first of the two motors I purchased. They arrived with the screws mostly out on both ends of both motors as the picture of the one I have not touched here shows.
New Motor1 - Screw out.jpg
 
This led me to the question of "Why in the devil are these screws not screwed in as on my old motors"? So, being the person I am, which is often foolishly curious, I proceeded to take apart the second brand new perfectly good motor just to see where indeed this screw goes. So I screwed in one of them to see if it would touch the worm gear or go into it's center to support it or some such thing. Again, if it needs that, why did they arrive with the screws not screwed in. I perseverate about such silly things. But, it was different.....WHY says my mind. Here's a pic of the one I screwed in. Seems there's still a tiny amount of clearance between screw and worm gear (though I have not powered the motor yet to see if it drags or not).
New Motor2 - Screw in.jpg
 
So, kids, what is the answer? Screws in? Screws out? Or maybe I just have screw loose? God (or one of you wise old G scale travelers) help me..........
 
Well they are obviously to control end-float..

Another thing I would check.. Are the 'old' and 'new' screws the same length? - Perhaps they are longer screws on the new block?

I would look to how much float there is on the old block, and possibly copy that??

Though I think I would (personally) tighten them equally to just-touch, then back-off half a turn..
That way, float is controlled, but there is a little 'wiggle-room'.. :nerd:
 
Probably just a production line worker not following or following a new procedure for assembly of the motor block. Not an unusual occurrence especially if from a different batch from the those that went into your F3 when it was born ;) Max
 
Ok, i tend to agree with the float reasoning. Good thought to check the screw length on the old motor. If they are the same, and there is no drag, i'll probably screw them in in the new motors and call it good.
 
I screwed up, the current USAT motor blocks do not have the screws, but apparently older ones, nicely caught Paradise!!!! Mia Culpa!

I bought that F3 quite some time ago.

The screws want to be turned in until you hear it slow down the motor, just touching, and then back off a bit.

You ideally want to move them in to reach the motor shaft without offsetting it one way or the other. If it's hard to do by feel and sound then maybe opening the unit, removing the axles and then you can see, but be sure to reassemble the axle bushings properly, that is the #1 reason of gearbox destruction. Please be sure the axle bushings look like this:

coveroff.jpg


Below is wrong: (in more than one way, pay attention to the brass bearings)
44tonner_destroyed.jpg


If you cannot see the difference in the orientation of the brass bushings between the two pictures, DO NOT open the motor block.

Greg
 
Yeah, you don't want a screw from one side to be offsetting the shaft otherwise it could be loaded against the opposite motor bearing rather than the opposite screw.
Those little square brass wheel bushes are problematic on reassembly. They will spring up by the pick-up wires and pop out of their seats or turn 45 degrees etc.
If the motor blocks are removed from the locomotive, the axles/bushes can be held in correct place with a stretched rubber band looped over each axle end making it easy to put the cover back on.

Greg, do you think the more recent blocks without the screws have different motors with perhaps more robust shaft bearings to stop excessive end float wear or are the just the same?
 
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If USAT has followed LGB and Bachmann, improved motors with internal thrust washers have eliminated the need to mechanically and externally control the motor shaft excursions.

I assume the newer motors were just phased in, like LGB did. The newer motor will work fine in the older motor blocks. The trick is how to know a newer motor.

Normally the motors in USAT outlast the gears and the motor block housings.

Greg
 
I agree that reassembly is much easier by stretching a rubber band from axle to axle around the top of the brick. Interesting that I had done that and reassembled the thing that way before I saw that Paradise had suggested that.
 
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