{
 "version": "2026-10-20",
 "license": "Dimension sheets are written by Xem Studio from the cited sources and are free to use (CC BY 4.0, attribute 'Xem Studio'). Linked files belong to their publishers under the license shown; Xem Studio does not host them. 'license_verified: false' means the license shown is from memory or the publisher's page as last read and should be confirmed at the link before commercial use.",
 "slug": "free-piston-cylinder-liner",
 "name": "Free-piston cylinder liner Ø30 × 120 and Ø40 × 160",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "What size cylinder does a free-piston Stirling core use?",
 "tags": [
  "free piston",
  "liner",
  "cylinder",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "free piston stirling cylinder",
  "cylinder liner 40 mm",
  "fpse liner"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 2,
 "url": "https://xemstudio.com/objects/free-piston-cylinder-liner/",
 "sheet_txt": "https://xemstudio.com/objects/free-piston-cylinder-liner/sheet.txt",
 "sheet": {
  "basis": "Bore 30 / 40, length 4 × bore, 3 mm wall",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The bore that the displacer and power piston share in the beta free-piston core: Ø30 × 120 (Ø36 outside) or Ø40 × 160 (Ø46 outside), 3 mm wall.",
   "The displacer runs in it with a 0.5 mm radial gap, the power piston with 0.05 mm, and the stop bumpers fit its bore (fit: press)."
  ],
  "table": {
   "columns": [
    "file",
    "bore",
    "outside",
    "length",
    "wall"
   ],
   "rows": [
    [
     "cylinder-liner-30x120",
     30,
     36,
     120,
     3
    ],
    [
     "cylinder-liner-40x160",
     40,
     46,
     160,
     3
    ]
   ]
  }
 },
 "sheet_text": "Free-piston cylinder liner Ø30 × 120 and Ø40 × 160 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/free-piston-cylinder-liner/  (CC BY 4.0)\nBasis: Bore 30 / 40, length 4 × bore, 3 mm wall\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The bore that the displacer and power piston share in the beta free-piston core: Ø30 × 120 (Ø36 outside) or Ø40 × 160 (Ø46 outside), 3 mm wall.\n- The displacer runs in it with a 0.5 mm radial gap, the power piston with 0.05 mm, and the stop bumpers fit its bore (fit: press).\n\nfile  bore  outside  length  wall\ncylinder-liner-30x120  30  36  120  3\ncylinder-liner-40x160  40  46  160  3\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- NASA (NTRS, public domain): Free-piston Stirling engine design and analysis (RE-1000 test results) (1984) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=19840017543\n- NASA (NTRS, public domain): Dynamics of free-piston Stirling engines (1987) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=19870011457\n- Wikipedia: Free-piston engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Free-piston_engine\n- Wikipedia: Beale number — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Beale_number\n- Ohio University: Stirling cycle machine analysis (Urieli), free online — web — Author's site — https://www.ohio.edu/mechanical/stirling/\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/free-piston-cylinder-liner/index.json\nAPI: https://xemstudio.com/api/geometry?object=free-piston-cylinder-liner\n",
 "sources": [
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Free-piston Stirling engine design and analysis (RE-1000 test results) (1984)",
   "url": "https://ntrs.nasa.gov/search?q=19840017543",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Dynamics of free-piston Stirling engines (1987)",
   "url": "https://ntrs.nasa.gov/search?q=19870011457",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Free-piston engine",
   "url": "https://en.wikipedia.org/wiki/Free-piston_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Beale number",
   "url": "https://en.wikipedia.org/wiki/Beale_number",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Ohio University",
   "title": "Stirling cycle machine analysis (Urieli), free online",
   "url": "https://www.ohio.edu/mechanical/stirling/",
   "formats": [
    "web"
   ],
   "license": "Author's site",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "free-piston-displacer",
  "free-piston-power-piston",
  "piston-stop-bumper",
  "borosilicate-test-tubes",
  "tri-clamp-spool"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "free-piston-displacer",
     "why": "displacer inside"
    },
    {
     "slug": "free-piston-power-piston",
     "why": "piston inside"
    },
    {
     "slug": "piston-stop-bumper",
     "why": "bumpers in the bore"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "borosilicate-test-tubes",
     "why": "glass tube bores"
    },
    {
     "slug": "power-cylinder-liner",
     "why": "flanged liners Ø16–30"
    }
   ]
  }
 ],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [
  {
   "feature": "rod bores",
   "exact": "Ø5",
   "mates": "Ø5 rod",
   "fit": "slide",
   "files": "all"
  }
 ],
 "fit_classes": {
  "press": "stays put: pin, tube, bearing or magnet held by interference. Typical FDM: hole +0.0 to +0.1 mm on diameter.",
  "slide": "assembles by hand and is held by a grub, pinch or clamp: shaft in a hub, rod in a socket, spigot in a bore. Typical FDM: +0.2 mm.",
  "run": "turns or slides in use: pin in a link, rod through a guide. Typical FDM: +0.3 mm.",
  "socket": "large sliding fit: syringe barrel, sleeve, bobbin in a bore. Typical FDM: +0.3 mm.",
  "clamp": "split part that closes on the mating part with screws: make it at size.",
  "designed": "a gap that is part of the design (piston fit option, displacer gap, air gap): do not change."
 },
 "faq": [
  {
   "q": "How long is the free-piston cylinder?",
   "a": "Four bores: 120 mm for Ø30, 160 mm for Ø40, room for displacer, piston and stops in one bore."
  },
  {
   "q": "What runs in the liner?",
   "a": "The displacer (0.5 mm radial gap) and the power piston (0.05 mm), one behind the other."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "cylinder-liner-30x120",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/free-piston-core/cylinder-liner-30x120.step",
   "stl": "https://xemstudio.com/files/hardware/free-piston-core/cylinder-liner-30x120.stl",
   "note": "cylinder liner Ø30 bore × 120, 3 wall"
  },
  {
   "file": "cylinder-liner-40x160",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/free-piston-core/cylinder-liner-40x160.step",
   "stl": "https://xemstudio.com/files/hardware/free-piston-core/cylinder-liner-40x160.stl",
   "note": "cylinder liner Ø40 bore × 160, 3 wall"
  }
 ],
 "markdown": "https://xemstudio.com/objects/free-piston-cylinder-liner/index.md"
}