be VERY careful with the wheels, i actually recently discovered it, in order to pop them off you need to get a decent sized flat head screw driver, put the tip all the way under next to the axle, and slowly turn the screwdriver and it will pull them apart, you may have to move the screwdriver around the wheel and repeat the turning motion to pull it off.... and thats the easy part
the hard part is pushing the wheels back together, you must be careful, it can be hard to push them back together, and if you dont push evenly on the wheel you risk bending the axle!!!!
the first time i took the wheels of an engine i had one hell of a time putting them back on, but the engine wasn't repairable or driveable anyway, soo i never did get them back on fully... but in your case, it would most likely be worth the trouble