UPDATE: Nuts/Bolts/Holes enlarged to make printing easier. You can also skip the printed nuts & bolts opting to use real M3 bolts if you want.
Working piston and rod with wristpin, threaded rod bolts, washers, and nuts. The real wristpin retainer was going to be tricky, so I just made two tapered pins to wedge in at angles inside the piston instead.
100% parametric, but complicated. Scaling should be no problem, but you may need to tweak the settings to compensate if you make things too out of proportion.
The parts are broken out into 3 plates:
- Rod half.
- Piston + wristpin.
- Bolts, washers, nuts, and tapered pins for the wristpin.
- Hold the two rod halves back-to-back.
- Place the nuts in the nut traps on the rods.
- Hold the rod cap halves back-to-back, then place against the rod.
- Add the bolts & washers from the bottom and screw into the nuts.
- Line up the wristpin holes in the rod and piston.
- Push the wristpin through one side of the piston, through the rod, and finally through the other side of the piston.
- Press the two tapered pins into the wristpin.
- If the friction from the bolt heads/washers pressing against the bottom of the rods doesn't hold the two rod halves together, just glue the two rod halves together.
- Slice the nuts/bolts plate using your thinnest layer height possible. The threads may be too small to make this usable, but proportionally the engine block that these fit is already over 100mm tall. Use real M3 nuts/bolts instead if you can't print things this small.