Clearance-seal displacer for a Ø40 liner: Ø40.00 running land, Ø38.50 body, 106 long — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/stirling-clearance-seal-displacer/  (CC BY 4.0)
Basis: Design values; shuttle loss after Martini; land and gap sizes set by the cycle model
Catalog version: 2026-10-20

Sizes: see table below
- The gas must go through the slotted heater, screens and cooler, not round the displacer. A short running land Ø40.00 × 8 at the cold end is a clearance seal in the liner bore; the body behind it is Ø38.50, a designed 0.75 mm radial gap that keeps the shuttle conduction low (the land is cold, the gap is where the temperature changes).
- Stroke 30 mm in both engines; the cold face comes to 10 mm from the hot spool's face and the hot end to 3.4 mm from the floor.
- The cap's Ø0.5 vent lets the inside follow the mean charge slowly, so the shell never carries the charge pressure; the rod screws into the cap's M6 hole and is locked by an M6 nut on the cold face.

part  od_mm  length_mm  fit
cap land  40.0  8.0  run (liner bore)
cap spigot  36.5  6.0  press (shell bore)
shell  38.5  98.0  designed 0.75 gap

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- NASA (W. R. Martini): Stirling Engine Design Manual, 2nd edition, NASA CR-168088 (1983): decoupled second-order losses (shuttle, conduction, flow friction, regenerator) — PDF — US government report — https://ntrs.nasa.gov/citations/19830022057
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/stirling-clearance-seal-displacer/index.json
API: https://xemstudio.com/api/geometry?object=stirling-clearance-seal-displacer