Crank discs, connecting rods and flywheels for model engines — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/crank-conrod-flywheel-kit/  (CC BY 4.0)
Basis: Parametric parts sized for 3 mm crank pins, 623 bearings (3 × 10 × 4) in the rod ends, and 5 / 8 mm shafts; proportions from the Long Earth Society tri-clamp engines
Catalog version: 2026-10-20

Sizes: see table below
- Crank disc: pin hole at stroke/2 from the bore; 3 mm dowel pin pressed in (2.95 mm hole in metal, 3.2 mm printed then reamed). Set screw locks the disc to a 5 mm shaft.
- Con-rod: 10.2 mm pockets take a 623 bearing at each end so the rod runs on balls, not plastic; centres 30–80 mm. Rod length ≥ 2 × stroke keeps the piston side-load low.
- Flywheel: energy ∝ D⁴, so go wide and thin: Ø100 × 10 mm in PLA with a brass rim insert outruns Ø60 solid. Balance by drilling the heavy side after the first run.
- Long Earth Society: the 2 in tri-clamp engines use a 20 mm stroke, 50 mm rod and Ø100 flywheel on an 8 mm shaft in 608 bearings.

part  sizes  shaft_or_pin  bearing
crank disc  stroke 10, 15, 20, 25, 30  Ø5 shaft, Ø3 pin  —
con-rod  centres 30, 40, 50, 60, 80  Ø3 pins  623 both ends
flywheel  Ø50, 80, 100, 120, 150 × 10  Ø5 (50) / Ø8  608 on the shaft

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Crank (mechanism) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Crank_(mechanism)
- Wikipedia: Flywheel — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Flywheel
- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine
- Long Earth Society: Engine builds that use these parts (videos and write-ups) — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 15 parts): https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/index.json
API: https://xemstudio.com/api/geometry?object=crank-conrod-flywheel-kit