Installing motor in 4-8-4, not a j

[rustycoupler]

 Whats the best way to remove the wheels and still keep them in quarter? 

[gatrhumpy]

That would be a tall order, but you might be able to do it if you put tape on each side and then gently lift out the drivers. However, seeing as how much freeplay this thing has in the drivers, it would be better to just requarter them after you intall the new motor.

[Mike C]

Leave all of the rods connected , and only take them out as far as you have to . It's a split frame ?  Usually you can remove the cylinders and wheels as a unit .

[James in FL]

Hi rustycoupler,

Are you talking about removing the drivers from their axles?
Or just removing the entire driver assembly?

If you just want to remove the entire assembly then @Mike C advice is sound and it's also the way I do it.
Leave them together unless there is some reason to remove the side rods, and related linkage from the drivers, this way quartering should not be an issue.

I just recently had mine apart.
If you have not had it apart to this degree before, you might find it helpful to photograph each side close up so you can see how the drivers are positioned, in their rotation, to each other.

Be aware the pony truck picks up power to the fireman's side of the frame, and the trailing truck to the engineers side of the frame.
There is a small phosphor bronze spring between the pony truck and the frame, this has to have some spring to it on reassembly, so be delicate with it.
You may have to adjust it so it is actually contacting both, this is mostly trial and error.
The third driver pair has the traction tires, this pair is not pined to the side rods and should be removed first, upon the removal of the bottom plate, and then the rest of the drivers and linkage removed as one unit.
Be mindful of the crossheads, unscrew from the frame, and then just pull apart (open) to remove the cylinder linkage.
The crosshead assembly has long tabs, which fit into the frame halves, between the first and second driver pairs.
Use either small needle nose, or hemostats, to remove them from the slots in the frame.
Be careful here, as these are easily broken, don't ask how I know.
The three rear drivers are geared, it may take a time or two to get them right, positioned correctly back in sequence with each other, then just align the counter weight on the traction tired driver, it will want to rotate slightly as it drops onto place.

It is paramount that the drivers are in perfect alignment with each other upon reassembly.

It's a piece of cake, especially the second time around.
After all is good, then press the crosshead assembly tabs back into the frame halves, and put the bottom plate back on.

As @gatrhumpy states, the mechanism has lots of slop in it, typical of Bachmann locomotives.
Tolerances are very loose.

Look here for reference;
https://www.youtube.com/watch?v=x8rqb64V__0

What's wrong with your motor?
What motor are you planning to replace it with?