This page describes how I converted my Kato passenger cars from their factory couplers to Micro-Trains' Z-scale couplers. The first photo shows the car in it original condition. The problem with the Kato couplers was that they didn't stay coupled. I remember one day when I had my 10-level helix for "P & C Railroad" version 3 and I was taking a long passenger train up the helix, it got to near the top when the second car uncoupled from the first. They must have set a new land-speed record by the time they got to the bottom of the helix! All cars came out unscathed, but still... The couplers had to be replaced.
Converting the Kato couplers from the truck-mounted couplers to the body-mounted Z-scale couplers involves removing the coupler from the truck, creating a shim piece, and gluing the shim piece and coupler to the body. Here are the tools I use to accomplish this task: scale ruler, small pair of pliers, small philips screwdriver, small pair of nippers, 0.010" piece of styrene sheet, a cutter for the styrene, 5-minute epoxy, black or stainless steel model paint, and a small paint brush. While I am at it, I also check the gauge of the wheels, hence the gauge checker tool in the photo.
Because the glue only lasts for a few minutes before it becomes unusable, I prefer to convert both couplers on the car at the same time.
Remove the trucks using the small philips screwdriver.
The Kato couplers are part of the truck body, so we need to cut it off. To do this, I first pop the axle nearest the coupler off of the truck body by gently widening the truck side frames.
Cut the coupler off of the truck using the pair of small nippers. File the rough cut down. This is not really visible during normal usage of the car, so getting it close is good enough. Reinstall the axle back on to the truck.
Cut a shim piece from 0.010" thick styrene. It needs to be 9 scale feet long and about 2 scale feet wide. File or sand the shim piece smooth. Double-check that that is indeed enough thickness to have the coupler clear the outside body of the car. Use the Micro-Trains gauge and test fit to see if the shim piece is indeed enough to have the coupler sit at the right height.
I prefer to uncouple cars manually (a pointy toothpick works great), and so I don't particularly care for the metal uncoupling hook on the Micro-Trains couplers. I, therefore, prepare the coupler by cutting off the metal hook using a pair of small nippers. The top of the metal hook needs to be cut off too to prevent it from interfering with the passenger car body's door.
Prepare the 5-minute epoxy. Glue the shim pieces of styrene to the passenger car's underframe. Use the glue sparingly. Make sure that it stays away from the outer body, just in case the glue oozes a bit. Wait a minute or so, to let the styrene piece settle (else it will move on you when you're installing the coupler). Glue the coupler in the center of the car body's opening and flush with the outside of the car body. Not all of the coupler box is supported by the shim piece. Put the small screwdriver handle or something relatively weighty on the coupler body to hold the whole thing in place.
Let dry for at least 5 minutes. Then test durability. Re-install the trucks.
Paint the shim styrene black or stainless steel to match the underframe of the car. The shim isn't really visible during operation, but it looks nice should you flip the car over. The final photo shows the coupler in action.