UPDATE: Improved version requires no supports and fits better in the headlight casing. V1 remains available if you prefer.
The Honda Urban Express NU50 / NU50M is a moped produced from 1982 to 1983. It uses a rare, discontinued sealed beam assembly for the main headlight and when they can even be found, they are only available expensively as NOS or used. This adapter attaches to the rear of the headlight, and adapts a cheap 1157 holder and bulb to the assembly.
Link to 1157 bulb holder: https://www.amazon.com/dp/B01LWUUVGV
Settings for printing:
Infill: 15% (not critical)
Perimeters: 2 minimum
Seam Alignment: Rear (this is to serve as an assembly mark to orient the adapter correctly)
Orientation on build plate: Use included .3mf file or refer to pictures. Seam points toward the bottom screw.
Printing note: Expect a very close fit between the 1157 holder and the adapter. You will likely have to shave off the inner seam. This close fit is on purpose. If you struggle to print an adapter that fits with only a little adjustment, let me know and I'll size the inner diameter up very slightly. Scaling the part may not produce good results.
VERY IMPORTANT: A headlight with high/low beams REQUIRES the adapter be oriented correctly. This is because headlights use the slight offset between the two filaments to reflect the light a little higher. If you print with the seam in the right place, this seam should be exactly in line with the bottom of the lamp, pointing toward the center mounting screw hole. The first picture shows this alignment.
Also, the 3mf file has the part in the correct orientation. If you don't have a Prusa MK4, open it for study, and align the STEP file correctly. This will place the seam in the right place to serve as a guide.
IF THE SOCKET IS UPSIDE DOWN WHEN INSTALLED, HIGH BEAM WILL NOT WORK CORRECTLY. THE WIRES SHOULD POINT DOWNWARD TOWARD THE BOTTOM OF THE LAMP.
Assembly is as follows:
1. Cut off the existing headlight bulb and wiring, and grind any remaining ridge flat. Break out and remove the old and remaining assembly, taking care not to break the front glass.
2. Use a step bit (https://www.amazon.com/Neiko-10174A-Change-Spiral-Grooved/dp/B089T8HJHF for example) to widen the hole just large enough to allow the 1157 bulb to pass.
3. Lightly sand the back of the lamp to remove any residues and provide a good gluing surface.
4. FIT TEST THE HOLDER TO THE ASSEMBLY FIRST. Super glue (semi-permanent) or epoxy (permanent) the adapter over the hole. If you cut the hole just large enough to accept the bulb, push it gently through the adapter and hole to help align it.
5. Create your wiring harness by using butt connectors, or spade or bullet removable connectors, to join the wires. Wiring is as shown in the picture.
6. After the glue or epoxy is dry, mount the bulb and holder to the adapter.
Reinstall the headlight to the holder if you've removed it, and reinstall the headlight assembly. You may have to slightly reroute the wires--it helps to wind the headlight wires loosely around the adapter.
Start the moped and test the light. If mounted correctly, low beam should point toward the ground a few tens of feet ahead. High beam should point almost parallel to the ground, casting a brighter beam further away. Adjust the headlight as needed for best visibility.
NOTE: This is a work-in-progress. I would like help perfecting the bulb distance to get the best focus. Also, if a more commonly-available 1157 socket can be found, please let me know. This was just the first one I could find with good mounting features.
The author marked this model as their own original creation.