Replacement valve part for The Source 51877 Air Powered toy car kit

thingiverse

The Source 51877 Air Powered Car kit is widely available at various resellers, with ours coming from a museum shop. This Amazon-listed car features a two-cylinder air engine where the cylinders pivot and move in unison, their reciprocating motion linked to a piston-like valve assembly. As this secondary valve-piston slides up and down its small cylinder, it alternately spans the inlet and outlet ports, coupling pressure to the power cylinder on a power stroke, and exposing the outlet port to the atmosphere as the power piston moves back on its exhaust stroke. When children take apart such delicate mechanisms without consulting the assembly instructions, they often break one or both of these valve rods, which are not easy to repair with glue. I managed to fix mine using very careful degreasing, specialist adhesive, and a binocular microscope, but it's a fiddly process unlikely to succeed in the long run. While taking it apart, I measured the mechanism and created an STL file for printing this part in two halves, which can then be glued together with cynoacrylate. Lining up these halves will be challenging, and while it could be printed in one piece with supports, significant clean-up would be required. Printing upright is not recommended due to the risk of snapping along print layers, although it might work with a laser-cure resin printer. This part requires some detail and cannot have an extremely rough finish, as the O-rings do the sealing. You could replace the printed pin in the trunnion with a pair of holes and use a separate metal or plastic pin, but the printed one should work fine. The model is not under heavy load when installed, but easy to break when taking it out or putting it back. The O-rings are custom-made, and the model comes with spares, which you might lose before breaking them. Astonishingly, no O-rings were lost in our case due to rough disassembly. Finding replacements is a challenge; take measurements from any remaining O-rings on the broken part, as they're all the same. If necessary, use thin silicone hoses and carefully slice off a little bit with a razor blade to replace an O-ring. Here's an STL file for a replacement valve rod, which can be printed in two halves without support – print both and glue them together. Lining up these parts will be a pain if you use CA, as it sets quickly. I use "foam safe" CA that I set with an activator or even moisture from my fingers to give me some time to adjust it.