Gamma crank head for a 2 in tri-clamp spool: rod gland, crankshaft towers and power-cylinder seat in one part — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/gamma-crank-head/  (CC BY 4.0)
Basis: ISO 2852 cap face (the end-cap profile) on a pedestal clear of the two-bolt clamp; 625 bearing (5 × 16 × 5) pockets; Ø20 × 45 flanged liner seat (flange Ø44, 4 × M3 on Ø36); all positions from the gamma crank train worked out in tools/gamma_geom.py
Catalog version: 2026-10-20

Sizes: see table below
- One part closes the spool's cold end and carries the whole crank: the ISO 2852 face clamps to the spool like an end cap; a Ø50.8 pedestal rises clear of the clamp to a deck at 14–22 mm.
- Displacer rod: a Ø3 bore runs straight through the cap, pedestal, deck and a Ø10 boss to 40 mm, a 40 mm clearance-seal gland for the Ø3 rod (the running fit is listed under Mating features).
- Crankshaft: two towers (x 15.5–23.5 and 55.5–63.5) with Ø16 × 5 pockets for 625 bearings put a Ø5 × 80 shaft 127.5 mm above the face, along the deck. Tower A's pocket opens toward the rod axis, tower B's toward the power cylinder, so the crank discs and spacers on the two shaft ends hold the shaft between the bearings.
- Cranks are overhung: the displacer disc on the x = 3.5 end puts its con-rod on the rod axis, the power disc on the x = 83.5 end puts its con-rod on the power cylinder axis (x 87); the flywheel turns between the towers, Ø150 clear of the deck by 30.5 mm.
- Power cylinder: the Ø20 × 45 liner's flange sits on a Ø44 seat (top 47.8 mm) with four M3 tapped holes (Ø2.5) on R18; the seat is the cylinder head. A Ø4 passage runs from the cap face at x 15 up into the deck, along it at z 18, and up into the liner: the transfer port, with no tube.
- Exact dimensions: pockets, bores and holes are drawn at the bearing, rod and tap-drill sizes; their fits are under Mating features.

feature  size_mm  position_mm
ISO 2852 face  2 in (Ø64 rim)  z 0
pedestal  Ø50.8  z 4.5–14
deck  141 × 54 × 8  x -30..111
rod gland  Ø3 × 40  on the axis
625 pockets  Ø16 × 5  z 127.5; x 15.5–20.5 and 58.5–63.5
liner seat  Ø44, 4 × M3 tapped on R18  x 87, top z 47.8
transfer passage  Ø4  x 15 → 87 at z 18

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine
- ISO: ISO 2852 clamp pipe couplings (face profile) — standard — ISO [verify license at link] — https://www.iso.org/standard/7873.html
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/gamma-crank-head/index.json
API: https://xemstudio.com/api/geometry?object=gamma-crank-head