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

thingiverse

The air-powered car kit (see picture) is widely available from different resellers. I think ours came from a museum shop. It's called "The Source 51877 Air Powered Car" on Amazon. It's s a two-cylinder air engine in which the cylinders are pivoted and move - the reciprocating cylinder movement is coupled via an arm to a piston-like valve assembly - as this secondary valve-piston slides up and down its small cylinder, the volume between the sets of O-rings is moved back and forth, alternately spanning the inlet and outlet ports to couple 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 your small child decides to take it apart without reference to the order in which it was assembled, chances are one or other of these delicate valve rods will get broken, and they are not at all easy to glue back together. I managed it with very careful degreasing and specialist glue and a binocular microscope, but, really, it's fiddly as hell and very unlikely to work out in the long run. So while it was apart I measured it up and created this STL. Print in two halves and glue together with cynoacrylate ("Super Glue" (UK), "Crazy Glue" (USA), "Sekund Kleber (De)" etc. Lining up the halves will be a challenge. Could print in one piece with supports but would need significant clean-up. Not recommended to print upright as likely to be more inclined to snap along print layers, but could perhaps print upright in one of those laser-cure resin printers, not sure. Certainly, this is a small and detailed part and while it doesn't need an immaculate finish (because the O-rings do the sealing) it can't be too rough. 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 OK. It's not under any massive load when installed, but easy to break when taking it out or putting it back. The O-rings are bespoke. The model comes with spares which, if you're like us, you will have lost before this gets broken. Astonishingly, no O-rings were lost to rough disassembly in our case... Good luck finding replacements... the dimensions can be taken from any of the O-rings that still cling to the remains of the broken part, they are all the same. At a pinch, take any of the thin silicone hoses from the model and carefully slice off a little bit with a razor blade, it should be about the right size to replace an O-ring. Here's an STL of a replacement valve rod, and half a rod for printing without support - print two and glue them together. Lining them up will be a pain if you use CA as it sets very quickly. I use "foam safe" CA that I use for model aircraft foam - it sets a lot slower unless you use an activator, so you get a short opportunity to adjust it. Note that moisture from fingers seems to make an effective activator for this stuff...