Since my previous post, i did the DEED
i (just for you!!!) disassembled my old 2018-very first version-substantially the same as your 2028 but for less lateral play in the middle drivers.
first, the idler sits in U shaped slot, accessible only from the top; it drops in
you must remove the motor block from the superstructure.
i sat mine upside down in the styro coffin for ease. be mindful of the headlight and stack, and pop valves, none are robust and should not bear the locos weight, imho.
remove the screws and washers that attach the drive rod to the connecting rods. play attention to how many washers are fitted and where ; once the drive rod (angled from the cylinders is removed, then gently prise the brass stabilizing stancheons from the cow catcher;
remove the screws from the bottom of the cab (4), remove the screws from the sides, ie those in the firebox on the sides, finally, remove the screw on the motor block bottom closest to the pilot truck , it is long and goes into the body, at least mine is, diagram shows a shorter screw, perhaps my threads were stripped at some point???; btw mind the sprung plunger for the lead pilot truck when replacing, it can push out and needs to be fully reseated before re-screwing things on the bottom plate.
once this is done the motor block can be lifted and turned over;
remove the three colored wired from their pins (pay attention to colors and position)
the block top lid has 4 screws, loosen and you will have access to the idler and the motor, but NOT to removing the drivers (that is done from the bottom side.) note that this cover slide under a couple of tabs when refitting. if you dont, it wont be properly flush with the block sides.
my loco does have thrust ball bearings. They are well and deeply seated in a small housing at the ends of the motor shaft. if yours has these , a tried method, for me, is to grease up a pair of tweezers as 'stick em' , and either remove them and set aside, or, simply leave them in and paste them in with grease as a "glue'. these bearing are deceptively important for older motors, dont lose them. The replacement new motors dont need them. dont lose them in any event.
As for quartering, if necessary, i simply set all the protruding wheel rod supports (bosses) at 6 o clock , on one side. easy to eyeball and be accurate. and it must be dead accurate. And, if you must remove and reset the idler gear onto its axel, i would recommend that the gear sit in hot but not boiling water briefly for both the off and on aspect of gear replacement operation. A gear puller will save you damage. You can note the position on the axel, use tape or ink. then with the new replacement gear, set the gear and axel over an adequately deep slot, such as on (NOT in ie clamped) a vice, and using a small hammer, gently tap the axel until the gear is properly positioned.
BTW, I thank you for the incentive, as my old girl's rods were way grottier than i knew, lots of well oiled grit from rain spattering and dry summer winds, way too long ago. I have since done a complete tear down , wash up, and relube. btw graphite powder is , imho, best for the slide gears, if you chose to lube. it wont attract grit. as for the bosses and rod holes, I use a drop or two tops. oil collects grit. But it can be flooded away with lighter fluid, wiped with a pipe cleaner etc., and re lubed.
I suggest a good but safe degreaser, if you have the likes of pine sol over your side. dish detergent works, but, i find i need to remove much grease with a paper towel, wash, repeat, wash, rinse, and then use lighter fluid, old grease is quite water resistant. if you feel competent, tear it all down and clean and wipe individual parts for the best results. Be thorough, inside rod holes, bosses, etc., If not, you can safely use a soft bristled toothbrush and pipe cleaner on the assembly, should get it 90%+ clean. be gentle. rods look sturdy but can break. They are difficult to find and very expensive. I would not run your loco without the traction tires. why? grit and rounding of grooves. if you buy NOS tyres, and they look yellow and not clear, i suggest that you soak them for an hour or more in a slightly detergent solution to rehydrate to reduce chances of them splitting. not an issue if you can find recent parts stock.
I bought my old 2018, long ago, well used from my local hobby shop. It has many hours, but still runs beautifully, even with one driver being down to the brass. (which BTW, needs to be cleaned frequently to avoid pitting and micro arcing)
Hope this helps you.