Working with Urethane Castings

Castings should be thoroughly washed before painting. Mold release is used to prolong the life of the molds and will cause paint to adhere poorly. Use warm soapy water or a mild sink cleanser. Rinse in warm water and air dry.

Do not apply heat to dry PARTS or use VERY hot water TO WASH. Urethane will soften and distort if heat is applied.

Castings may need to have some flash, parting lines or sprue marks removed. A hobby knife and sandpaper works well. The urethane cuts and sands easily so use care. I prefer to wet sand. Use wet/dry sandpaper (320 through 600 grit) and keep the paper wet while sanding. Using water lessens the chance of scratching the castings and slows the cutting action of the sandpaper.

Even though every effort is made to provide a perfect casting some filling of imperfections may be required. I’ll wash the castings and spray a light coat of automotive primer on before inspecting and cleanup. The gray primer makes any imperfection highly visible and also provides a base that body putty can adhere to. After filling, the putty can be sanded down using wet/dry sandpaper as described above.

After the castings are finished to your liking they can be installed using slow setting cyano-acrylate adhesive or epoxy.

Remember that cyano-acrylate type adhesives usually bond urethane resins INSTANTLY! Slow curing types will only give you a slight increase in time to position your parts.

Installing Domes and Stacks on the Bachmann Mogul

The Bachmann domes and stack are glued to the boiler but the adhesive joint is not strong. In most cases gently rocking the parts from side to side while applying pressure will cause the adhesive to break loose. Gentle pressure is all that is required. If too much force is applied it is possible that some of the boiler material will chip out around the dome opening.

The domes and stacks are designed to fit into the molded holes in the boiler. Some minor cleanup of remaining adhesive or adjustment to the size of the holes may be required for a good fit.

Parts can be glued to the boiler with slow setting cyano-acrylate adhesive or epoxy. Be sure parts are square to the boiler and in line with each other. Any slight gaps between part and boiler can be filled with body putty. I prefer Squadron Green but any similar product will work.

Assembling Stack "Kits"

Some stacks are supplied with multiple parts and will require assembly. A stack "kit" consists of a base, cap and screen.

It is suggested that the parts for the stack be cleaned up as outlined above and the inside of the base and cap painted before assembly. Painting the inside a flat black will prevent seeing the inside of the stack through the screen.

The screen should also be painted before assembly so the back can be painted. Flat black is recommended and additional weathering such as rust can be added to the outside after final assembly and painting.

Be careful in applying paint as excessive buildup can mask the screen detail.

The screen is cemented in from the underside of the cap. A slight step is provided to locate it. In some cases the screen will need to be formed into a slight dome shape to fit. The screen can be cemented in with a few small drops of thin cyano-acrylate adhesive applied from the inside after the screen is in place.

The cap and screen assembly is then fixed to the body using cyano-acrylate adhesive.

Climax Stack Kits

In general the Climax stacks are assembled the same as other stack kits described above. A clearance hole will need to be drilled through the stack for the Bachmann mounting screw. To remove the old stack insert a small phillips drive screwdriver into the stack and loosen the screw at the base.

To locate the center spot for the screw hole take a 1/8 (0.125) diameter drill and insert it from the top side of the stack body. It will just fit into the cored hole in the base casting. Give it a couple of turns by hand to create a center spot. Use this spot to center a #50 (0.070 dia.) drill in a pin vise and drill through the stack.