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  • Converting the Atlas SD24 to the Union Pacific SD24m


    George Cockle photo.
    Prototype Modeler - December 1977 - Page 8 Prototype Modeler - December 1977 - Page 9


    Union Pacific's SD-24m, 3399, came onto the property as No. 423, a standard SD-24 built by the Electro-Motive Division of General Motors in 1959. Nine years later, this unit entered the Omaha Shops of the UP for a major up-grading and eventually emerged as the SD-24m. It was renumbered to 3100 at this time. Included in the up-grading was a re-engining with a prime mover very similar to those used in the road's SD-40s. The new engine incorporated a system to provide for constant speed engine operation (full throttle); control of the unit was through a special system that did not effect engine speed. In 1970, the locomotive was again renumbered to clear the way for the remaining number sequence in the road's SD-40 fleet; the new number was 3200. At that time the unit was also re-equipped with a standard throttle and now operates in the same way as a standard diesel. In 1973, the problem on SD-40 numbering again came up and the SD-24m was renumbered to its present 3399 number to make room for additional SD-40 units.

    George Cockle photo.
    Prototype Modeler - December 1977 - Page 10 Prototype Modeler - December 1977 - Page 11


    Building a model of this distinctive locomotive is not as difficult as it might first appear. All that is needed is patience and care, the end result will be achieved without experiencing any undue difficulty. Read through the article; this will give you a "feel" for the conversion and what is involved. If you're interested in the appearance of 3399 when it was delivered in 1959, there is a photo on page REP 454 of Kalmbach's Second Diesel Spotters Guide.


    Before getting into the conversion of the model itself, it would be well to check out the mechanism and iron out any slight difficulties that might be apparent. After assuring that the motor and power train are operating satisfactorily, remove the motor and trucks from the frame and set aside for later reinstallation. Using Figure 1 as a guide, remove the portions of the frame on the left side as shown. This step is most easily accomplished using a Dremel Tool but there are other ways that will also work though they may require a little more time and effort. A file will finish up this work well.

    The fuel tank on the model does not have the "heavy" look of the prototype that adds so much to the appearance of the model. Use a flat file and, as shown in Figure 1, round off the top comers and the bottom of the tank. Also, file the tank ends flat as shown in the illustration. Use a razor saw and cut a slot along the top of the tank (see Section C-C of Figure 1). There i s a wide groove in the side of the tank; fill this in with styrene held in place with one of the cyanoacrylate adhesives (we'll call it ACC in this article but any of this type of adhesives would do fine). File this to shape, fill the cracks with putty, and file smooth so that the tank groove will not show after the tank has been painted. Cut a 1/8" strip of .020" styrene and cement it in place with ACC cement along the bottom edge of the fuel tank ends and file flat to match the tank ends (see Figure 1).

    The next step is to cover the fuel tank ends with styrene and make a wrapper for the tank length. Cut two 1 1/2" x 5 /8" pieces of .020" styrene and cement them to the ends with ACC. These pieces should be roughly shaped to the ends with a little left extending over the edges for final finishing. Use a fine sandpaper on a sanding block and finish sand the styrene ends to exactly match the shape of the tank. Both right and left tank wrappers are made from .010" styrene. The right tank wrap per is 1 13/16" x 1" in size. The top edge of the wrapper should be cemented into the slot cut earlier with ACC. The styrene wrapper "wraps" around the tank; a couple of drops of ACC should be added while "wrapping" the wrapper and ACC used to secure the bottom edge. The left tank wrapper is 1 13/16" x 1 1/2". Two fuel tanks ends (1 1/2" x 5/8" x .020" styrene) should be added to the tank ends as above; the tank wrapper should be added in the same manner as was the right wrapper. Trim them both at the bottom and cut out the two motor screw holes. Apply putty to the joints and sand smooth when dry. At least a 400 grit wet or dry sandpaper should be used for final sanding.

    Fabricate the fuel vent lines referring to Figure 2; use .030" dia. brass wire. Make the U-bend as shown. Cut a 1/16" piece of brass tubing 3/32" long; slip it on the wire and solder (or use ACC) it in place as shown in the illustration. Cut a second piece of brass tubing to this same length and attach it to the wire as shown. Referring to the photos, note that the diameter of this second piece is slightly larger than the first; the diameter can be made greater with Scotch Tape or some similar type as long as it has a smooth surface. Cut a third piece of tubing 1/8" long and add that as above.

    George Cockle photo.
    Prototype Modeler - December 1977 - Page 12 Prototype Modeler - December 1977 - Page 13

    Before cementing the fuel tank vents to the frame, it is a good idea to assemble the body back on the frame to be sure that the fuel vent lines will clear the body when it is installed. When clearance is assured, cement the vent lines to the body with ACC. Wash the frame in warm water and detergent to remove all traces of handling and the changes made to the frame. Paint the frame using Scalecoat's U.P. Harbor Mist Grey. If, after painting, any tool marks, cracks or joints, or other blemishes show, correct them now and repaint. The top half of the fuel vent lines should be painted yellow to match the body. Use the photos with this article as a guide.

    Add the speed recorder drive to the front truck, middle axle, left side, according to the directions with the speed recorder casting. Clean the truck side frames, in the same way the frame was, and paint them silver.


    The following parts should be removed from the body and saved for reuse later on: the two weights, handrails, airtanks, horns, light conduit bars, and the number boards. The couplers and cab windows should be removed and tossed in your spare parts box for some other project they may be needed for some day. If the model to be converted is painted, it would probably be best to remove the paint. Brake fluid can be used as can any of the commercially available products marketed for this purpose - just be sure that it will not harm the plastic body shell.

    The following molded-on details should be removed format he body shell: allouvers, the half-round bulge and all the door latches on the long hood only. Also, remove the two molded-on ladders and grab irons on the end of the long hood, and the exhaust stack. File off the radiator grills and all the door latches below the running board on the right side. Remove all the molded-on pilot detail and cut off the foot boards; open up the coupler holes with a file to accept MKD-8 couplers if the model is to be equipped with Kadee's. The areas where these details have been removed should be sanded smooth with the 400 grit wet or dry sandpaper (this sandpaper may be a little slow but it gives a fine finish).

    The next step is that of adding the "chop-nose" of the prototype. This is not a difficult project but it does require care.

    Referring to Figure 3, measure three scale feet up from the top of the battery box and five scale feet up from the running board (Figure 3.) Scribe a line between these points continuing the slope to the front. The front of the nose is flat, not sloped. Cut the short hold just above the scribed line back to the front of the cab; cut the top of the hold down along the cab front. Remove the hood top and save it.

    Finish the bottom of the long hood by filling up to the bottom of the hold doors. Also, file the running boards smooth.

    As shown in Figure 4, cut out the dynamic break blister. Too, cut off the winterization hatch and the two fans but be careful not to amigo the fans as they will be used later.

    Cut a piece of .060" styrene to fit inside the radiator top. Cement this in place flush with the top. Next, cut two pieces of .060" styrene to fill in the side spaces where the dynamic brake was removed; these pieces should be level with the lower of the two top surfaces on the long hood. Laminate a sandwich of styrene sheet that is .130" thick; two sheets of .060" and one of .010" will serve well. Trim this laminated sheet to a scale size of 6' x 23'. Cement this to the top of the lower portion of the long hood with one end tight against the radiator; this will make the entire length of the top of the long hood the same height.

    Using .020" styrene, cut several strips a scale 1' wide (see Figure 5). Laminate some of these to give a .040" thickness; when laminating the strips, leave the area shown only.020" thick in the motor recess area. After the lamination has dried throughly, trim the strips to length and add them to the bottom of the long hood as shown in Figure 5. Be sure the motor recess areas are in the proper location. When all cement on the long hood is dry, apply putty to all joints and sand smooth. A couple of doors on the long hood have to be filled in and reshaped (see Figure 6). After completing the door modifications fill in the old outline of the doors and the latch recess holes; sand smooth. Put aside the long hood and start rebuilding the nose and cab front.

    Jan Podganski, Jr., photo
    Prototype Modeler - December 1977 - Page 14 Prototype Modeler - December 1977 - Page 15

    Nose rebuilding starts with a piece of 060" styrene to fit inside the opening left when the top of the short hood was removed; it should extend back to the cab front. Cement this in position and, when dry, use a file and round off the comers of the hood. Apply putty to the joints on the hood and, when dry, sand smooth. Again, use a 400 grit wet or dry sandpaper for all finish sanding.

    Refer to Figure 7 for the cab front re building details. Cut a 1/8" wide strip of .060" styrene to the width of the opening in the cab front; the top edge should extend 1/64" above the short chopped hood. Fill the top of this opening with a .060" strip of styrene 1/4" wide; cement in place. This will make the front window slightly too narrow; it should be opened by filing the bottom edge down 'till the opening is 3/16" wide. After the added pieces have had ample opportunity to dry, make a light hole 3/16" square. Make a new head light housing from the front hood that was cut out earlier (see Figure 8). Using a razor saw, make a horizontal cut both immediately above and below the head light rims; drop a vertical cut to remove this section just behind the number boards. Sand this piece square and add a piece of .010" styrene to form the bottom surface. Locate the bottom point for this section 3/32" x 3/32". Cement these in place at 1/4" up from the bottom of the window and fill the joints and sand smooth when and cement this section in place.

    After the headlight section has dried throughly, remove the classification lights from the angles panels. Carefully file the top of the headlight section to match the round shape of the cab roof. Then, file this edge down an additional .010" and cut a piece of .010" styrene and cement it over the headlight section to form a continuation of the cab roof. This piece should fit snugly against the cab roof; fill the joint and sand it smooth.

    Start to rebuild the rear wall of the cab by first removing what is eft of the original cab wall. The new rear wall should be made from .020" styrene. Shape it to the size of the cab itself plus slightly higher so it overlaps the cab roof. Mark and cut out the two rear windows; also, cut out for the flywheel. Cement the wall in place and, when dry, shape it to conform to the shape of the roof. Fill the joints and sand smooth.

    Now, back to the long hood. The radiator bulge on the model is not the correct length and must be extended. To accomplish this, refer to Figure 10 and make four squares of .040" styrene measuring 3/32" x 3/32". Cement these in place and fill the joints and sand smooth when they are dry. Again, referring to Figure 10, make two fairings from .040" styrene measuring 3/16" x 9/32". Cement in place and, when dry, file to a wedge shape as shown in Figure 10; fill the joints and sand smooth.

    The left side running board must be removed. Make the first cut (use a razor saw) just behind the rear wall of the cab and the second cut just behind the last hole for the handrail post.

    Next step is to cement the long hood back into its original position. Use a full measure of care and patience here; make sure that everything is level and straight. Use solvent cement to assemble the hood and cab but when everything is dry flow a little ACC over all the joints (on the inside of the shell) for a little added strength.

    The replacement of the left side running board is now at hand. Sand all the detail off the running board removed earlier. Fill the locations of the latches with putty and, when dry, sand smooth (do not fill in the holes for the handrail posts). File an angle on the rear end of the running board as shown in Figure 11. The running board should be narrowed to a width of 2 scale feet wide. Cut a piece of .040" styrene to fit as shown in Figure 11 and cement in place. When thoroughly dry, the running board should be reassembled to the long hood as shown in Figure 12. Make and install nine pie brackets to the dimensions shown in Figure 12.

    Jan Podganski, Jr. photo
    Prototype Modeler - December 1977 - Page 16 Prototype Modeler - December 1977 - Page 17

    A fairing must be made from .010" styrene to blend the long hood with the cab roof. See Figure 14. Refer to Figure 16 and cement it in place as shown. Make the side fairings from .010" styrene; add putty to all joints and sand smooth.

    New grilles must be fabricated for the long hood; they are made from Athearn running boards from their 50' mechanical refer kit. In some instances it will be necessary to thin down the running board thickness. This can best be done by placing a piece of sandpaper on a flat surface and moving the running boards back and forth using a block of wood for backup to get an even pressure over the surface. The radiator section is a good place to start. The radiator frame is made of .010" sheet styrene measuring a scale 2' x 14'; make two of them. Cut four sections from the Athearn 50' mechanical reefer running boards measuring 1'-6" x 6 '-6". Reduce the thickness of these sections according to the procedure mentioned above. These sections will be the radiator grilles. When done, cement them in place as shown in Figure 14 and set them aside.

    The dynamic brake grilles are next in order. These grilles should be cut from the Athearn running board to a size of 1' 1'-9" x 7'-3" in size. Strips of styrene should be cut and added along the edges of the grilles; when dry, they should be trimmed even with the top and bottom surfaces of the grille.

    The air filter grilles are also made from the Athearn running boards. These are 1'-9" x 4'-9", there are two. The air filter grilles have to be thinned down to .020" thickness. File the grilles true and square. Make a 2'-3" x 5'-3" frame from .010" styrene . The air filter grilles should be centered on the frame with a 3" space on all sides. The roof-top dynamic brake grille is a composite of four sections of Athearn running board. Cut two pieces of running board 1'-9" a 11'-0". Cut an additional piece of running board 1'-3" x 11'-0" and a last piece 1'-0" x 11'-0". Cement these together as shown in Figure 14, Dynamic Brake Hood Top Grilles; cement these together by joining the two right hand pieces and then the two left hand pieces (do not join these two sections together. Cut two 1/8" x 1 1/2" strips of .020" styrene; layout the left and right dynamic brake grilles as shown in Figure 14 and cement them in position. This will "peak" the grille for later addition to the hood top.

    The turbocharger bulge comes next. One removed from an SD-45 body shell is ideal other than its having to be thinned down suitably. This can be done using the same block method as was used on the roof running boards for the grilles. Remove the original panel. The bulge is too short so it will be necessary to add a piece of .060" styrene to the bottom of it. Fill the joints and sand smooth; this should be done at this point in time.

    Refer to Figure 16 and locate the position of the grilles and panels shown on the shell. Cement these components in position. Cut the air tanks apart, file them to their correct cylindrical shape and install them in their correct position.

    Detail the nose and cab as shown in Figure 17. The ATC box can be made by laminating styrene to the correct size. After installing the box, install an .010" wire from the front of the box down to the running board as shown in the illustration. The marker lights are made from .030" styrene filed to a wedge shape. Mount one on each side of the hood 1/2" up from the running board on the short hood and 1" up from the running board on the long hood.

    Install the grab irons; if Northeastern grabs are used, drill No. 76 holes where they insert into the shell. One grabiron goes on the right side of the short hood parallel to the hood side. On the long hood, one goes on each side of the head light just above the number boards. There are also two grabs just above these on the hood top. There are also two just above the ladders. For the circular railI used Walthers curved rail. The rear ladders are stamped brass ladder stock by Kemtron; use the photos as a guide to their proper location.

    Prototype Modeler - December 1977 - Page 18 Prototype Modeler - December 1977 - Page 19 Prototype Modeler - December 1977 - Page 20

    Using both Figure 18 and the prototype photos as a guide, install the MU hoses, MU receptacles, and plates. Fabricate two uncoupling handles and install them using Kemtron or Detail Associates eyelets to hang them.

    Using the Athearn running board material, make four 1'-0" x 3'-0" floor boards for the pilots and cement them in place with ACC.

    Make the air cooling pipe from .020" wire using the photos and Figure 19 as a guide. Install as shown.

    Running board grids can be made from vinyl window screening material (do not use copper or steel screening, its appearance is distracting). Refer to Figure 21 for the dimensional requirements.

    The final task is that of fabricating and installing the handrail posts and handrails. Make the handrails using .020" brass wire using Figure 20 as a guide for forming them. The handrail posts are the original posts supplied with the locomotive slightly; a No. 76 hole has to be drilled through each post for the handrail after the nylon handrail has been cut off. The railings are inserted through the posts and the posts installed on the shell.

    Check to make sure that everything is satisfactory; then wash the body shell in warm water and detergent. When dry, paint the shell with a grey primer coat. Check the modifications made to the shell and if there are any points that still need cleaning up it should be done now (when the shell has the primer coat applied every scratch and blemish stands out). Another primer coat should be added over the corrections if any were necessary. Use Scalecoat paints (or any other brand that you prefer though it may mean a little paint mixing is needed); the colors are UP Yellow and UP Harbor Mist Grey. Use the photos as a guide to painting. Apply the appropriate decals and weather to suit.

    Article Details

    • Original Author Jan Podganski, Jr.
    • Source Prototype Modeler
    • Publication Date December 1977

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