{
 "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": "alpha-v-twin-crank-disc",
 "name": "Alpha V-twin crank disc Ø26, one pin, 16 mm stroke",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What crank disc does a 90° V-twin alpha Stirling use?",
 "tags": [
  "alpha",
  "crank disc",
  "v-twin",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "v twin stirling crank",
  "alpha crank disc one pin",
  "crank disc 8 mm throw 5 mm bore"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/alpha-v-twin-crank-disc/",
 "sheet_txt": "https://xemstudio.com/objects/alpha-v-twin-crank-disc/sheet.txt",
 "sheet": {
  "basis": "90° V alpha: both con-rods on one pin; throw 8 (stroke 16)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Ø26 × 6 disc with a Ø5 bore (fit: slide) and a Ø2.5 radial hole (M3 tap size) for the grub screw.",
   "ONE Ø3 hole (fit: press) at 8 mm for a Ø3 × 20 crank pin; both con-rods ride it, one plane each, with 1 mm spacers and a 3 mm collar on the end.",
   "A two-pin disc with pins 90° apart under a 90° V would give 0° or 180° and the engine would not run; that disc is for parallel cylinders."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "disc",
     "Ø26 × 6"
    ],
    [
     "bore",
     "Ø5"
    ],
    [
     "throw",
     8
    ],
    [
     "stroke",
     16
    ],
    [
     "pin hole",
     "1 × Ø3"
    ],
    [
     "grub hole",
     "Ø2.5"
    ]
   ]
  }
 },
 "sheet_text": "Alpha V-twin crank disc Ø26, one pin, 16 mm stroke — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/alpha-v-twin-crank-disc/  (CC BY 4.0)\nBasis: 90° V alpha: both con-rods on one pin; throw 8 (stroke 16)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Ø26 × 6 disc with a Ø5 bore (fit: slide) and a Ø2.5 radial hole (M3 tap size) for the grub screw.\n- ONE Ø3 hole (fit: press) at 8 mm for a Ø3 × 20 crank pin; both con-rods ride it, one plane each, with 1 mm spacers and a 3 mm collar on the end.\n- A two-pin disc with pins 90° apart under a 90° V would give 0° or 180° and the engine would not run; that disc is for parallel cylinders.\n\nparameter  value\ndisc  Ø26 × 6\nbore  Ø5\nthrow  8\nstroke  16\npin hole  1 × Ø3\ngrub hole  Ø2.5\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n- Wikipedia: Stirling engine (alpha configuration) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/alpha-v-twin-crank-disc/index.json\nAPI: https://xemstudio.com/api/geometry?object=alpha-v-twin-crank-disc\n",
 "sources": [
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Stirling engine (alpha configuration)",
   "url": "https://en.wikipedia.org/wiki/Stirling_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "alpha-v-twin-syringe-frame",
  "pin-end-con-rods",
  "two-pin-crank-disc-90",
  "list-alpha-v-twin-syringe"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "alpha-v-twin-syringe-frame",
     "why": "on the shaft beside the boss"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "pin-end-con-rods",
     "why": "both alpha-conrod-60s on the one Ø3 pin"
    },
    {
     "slug": "stirling-crankshafts",
     "why": "Ø5 × 80 crankshaft, Ø3 × 20 pin"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "two-pin-crank-disc-90",
     "why": "for parallel cylinders"
    }
   ]
  }
 ],
 "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": "crank-disc bore",
   "exact": "Ø5",
   "mates": "Ø5 crankshaft (M3 grub)",
   "fit": "slide",
   "files": "alpha-crank-disc-"
  },
  {
   "feature": "crank-disc pin hole",
   "exact": "Ø3",
   "mates": "Ø3 × 20 crank pin",
   "fit": "press",
   "files": "alpha-crank-disc-"
  },
  {
   "feature": "crank-disc grub hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "alpha-crank-disc-"
  }
 ],
 "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": "Does a V-twin alpha need two crank pins?",
   "a": "No. In a 90° V both rods share one pin; the V gives the 90° phase."
  },
  {
   "q": "What stroke does the alpha crank disc give?",
   "a": "16 mm (pin at 8 mm), about 2.6 mL per 10 mL syringe."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "alpha-crank-disc-s16",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.step",
   "stl": "https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.stl",
   "note": "crank disc Ø26 × 6, Ø5 bore, Ø2.5 tap-drill hole for an M3 grub, ONE Ø3 pin at 8 mm (stroke 16): both con-rods share it"
  }
 ],
 "markdown": "https://xemstudio.com/objects/alpha-v-twin-crank-disc/index.md"
}