NU50 Honda Urban Express Fork Dust Boot

prusaprinters

This is a replacement fork dust boot for a 1892-1983 Honda Urban Express, the NU50 and NU50M models. These fork seals are unobtainable individually as they were only sold as part of a complete front fork tube replacement, and are long since out of stock. Replacing a fork seal requires disassembly of the front fork and inner tube. However, if you had a very good TPU glue, you could cut the finished part and glue it back in place over the tube, then assemble as normal.This part has a built-in surface covering the entire inner hole. This is to eliminate the need for supports in TPU, which are often very hard to get right. Cut this away with a sharp new blade and, for best success with cleanup, punch through, then cut on the rising stroke. This will reduce the number of strings to pull off later. Clean off any remaining bridging strings found by pulling from the base of the string with pliers.Print with the following settings:Nozzle: 0.4mm nozzleLayer Height: 0.2 layer height (finer layers are fine) Perimeters: 3 (or enough to print most of the outer wall solid) Infill: 15% (more is ok, but may make fitting over the outer tube very difficult or impossible) Supports: No supports  (the built-in bridging web supplies this). Speed up bridging for TPU to reduce sagging. Brim: Yes, if you have a textured or otherwise less-adhesive bed for TPU. Do not use if your adhesion is very good already.The most difficult part of disassembly will be removal of a shielded ring around the fork tube which holds the lower compression spring in place, and the removal of the inner tube spring buffer pad at the top, which requires drifting out the roll pin holding it in place.Drifting out the roll pin is best done with a roll pin punch (https://www.amazon.com/s?k=roll+pin+punch+set). A flat punch will not center on the roll pin easily, and can mushroom the pin end, making disassembly and reassembly more difficult. A sturdy work surface is required, a sturdy vise with soft jaws is ideal.To remove the shielded ring the easiest method is to simply drive the shield off the ring by tapping it off with a punch and hammer, working your way around the shield slowly to avoid bending. You can then remove the inner ring and shield separately. Assembly is the reverse. If the shield doesn't stay on the ring after this, find the peened marks on the shield and use a punch to drive them in slightly. Take care not to mar the lower face of the shield, where the lower springs and plastic slides touch.Then, install the new fork tube dust boot, closed end facing toward the wheel mount. Assembly is the reverse of disassembly.Clean any dirt you find, and replace any lost grease on the plastic slides on each part of the tube. Reassemble the inner fork tube to the outer, and push the new fork dust boot on. This will require substantial force, as TPU is less forgiving than rubber.Update: A version without the bridging support layer is now available to choose your own support method if you wish.