{
 "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": "htd-crankcase-caps-3in",
 "name": "3 in crankcase caps: blind bearing cap, seal cap and 3-port cap",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "How do I put bearings and a shaft seal in a 3 inch tri-clamp cross?",
 "tags": [
  "htd",
  "crankcase",
  "bearing cap",
  "tri-clamp",
  "stirling",
  "npt"
 ],
 "aliases": [
  "tri clamp bearing cap",
  "tri clamp shaft seal",
  "3 inch tri clamp port cap"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 3,
 "url": "https://xemstudio.com/objects/htd-crankcase-caps-3in/",
 "sheet_txt": "https://xemstudio.com/objects/htd-crankcase-caps-3in/sheet.txt",
 "sheet": {
  "basis": "Fabrication spec: 3 in cap profile with a Ø76.2 neck (the 20° back cone runs to the tube OD, then straight), bored and ported; exact geometry",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Blind cap (−X branch): a 6001 at the end of a Ø36 boss that reaches 20 into the branch. Seal cap (+X): a 6001 at the boss end and another near the outer face, the shaft seal's housing (12 × 22 × 7) at the outer face, three M4 holes for the generator bracket.",
   "Port cap (top of the cross): three 1/4 NPT ports for the fill valve, the gauge and the relief valve. The crankcase is the bounce space: it reaches the working space's mean pressure through the piston's fit and the rod bore.",
   "The shaft seal is the one leak path to the outside of a charged engine: it has to be a seal rated for the relief pressure in that housing size, and a charged engine will still lose helium slowly through it."
  ],
  "table": {
   "columns": [
    "part",
    "thickness_mm",
    "seats"
   ],
   "rows": [
    [
     "bearing-cap-3in-blind-6001",
     28,
     "6001"
    ],
    [
     "seal-cap-3in-6001-seal12",
     30,
     "2 × 6001 + seal 12 × 22 × 7"
    ],
    [
     "port-cap-3in-3x-npt14",
     16,
     "3 × 1/4 NPT"
    ]
   ]
  }
 },
 "sheet_text": "3 in crankcase caps: blind bearing cap, seal cap and 3-port cap — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/htd-crankcase-caps-3in/  (CC BY 4.0)\nBasis: Fabrication spec: 3 in cap profile with a Ø76.2 neck (the 20° back cone runs to the tube OD, then straight), bored and ported; exact geometry\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Blind cap (−X branch): a 6001 at the end of a Ø36 boss that reaches 20 into the branch. Seal cap (+X): a 6001 at the boss end and another near the outer face, the shaft seal's housing (12 × 22 × 7) at the outer face, three M4 holes for the generator bracket.\n- Port cap (top of the cross): three 1/4 NPT ports for the fill valve, the gauge and the relief valve. The crankcase is the bounce space: it reaches the working space's mean pressure through the piston's fit and the rod bore.\n- The shaft seal is the one leak path to the outside of a charged engine: it has to be a seal rated for the relief pressure in that housing size, and a charged engine will still lose helium slowly through it.\n\npart  thickness_mm  seats\nbearing-cap-3in-blind-6001  28.0  6001\nseal-cap-3in-6001-seal12  30.0  2 × 6001 + seal 12 × 22 × 7\nport-cap-3in-3x-npt14  16.0  3 × 1/4 NPT\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- ASME: ASME B1.20.1 Pipe Threads (NPT): 1/8-27 and 1/4-18, tap drills Ø8.6 / Ø11.1 as on this site's thread envelopes — standard — ASME; dimensions are facts [verify license at link] — https://www.asme.org/codes-standards/find-codes-standards/b1-20-1-pipe-threads-general-purpose-inch\n- Tameson (product listing): Rotary shaft seal 12 × 22 × 7 mm (DIN 3760 sizes) — web — vendor page; dimensions are facts [verify license at link] — https://tameson.com/products/s2avq-x20-nbr-design-a-rotary-shaft-seal-12x22x7mm-20-pieces\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, 3 parts): https://xemstudio.com/files/hardware/htd-crankcase-caps-3in/index.json\nAPI: https://xemstudio.com/api/geometry?object=htd-crankcase-caps-3in\n",
 "sources": [
  {
   "publisher": "ASME",
   "title": "ASME B1.20.1 Pipe Threads (NPT): 1/8-27 and 1/4-18, tap drills Ø8.6 / Ø11.1 as on this site's thread envelopes",
   "url": "https://www.asme.org/codes-standards/find-codes-standards/b1-20-1-pipe-threads-general-purpose-inch",
   "formats": [
    "standard"
   ],
   "license": "ASME; dimensions are facts",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Tameson (product listing)",
   "title": "Rotary shaft seal 12 × 22 × 7 mm (DIN 3760 sizes)",
   "url": "https://tameson.com/products/s2avq-x20-nbr-design-a-rotary-shaft-seal-12x22x7mm-20-pieces",
   "formats": [
    "web"
   ],
   "license": "vendor page; dimensions are facts",
   "license_verified": false,
   "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": [
  "list-htd-10in",
  "htd-crank-linkage",
  "radial-shaft-seal-12x22x7",
  "npt-thread-envelopes"
 ],
 "fits": [],
 "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": "faces",
   "exact": "ISO 2852 3 in (neck Ø76.2)",
   "mates": "gasket-3in + 3 in clamp",
   "fit": "clamp",
   "files": "all"
  },
  {
   "feature": "bearing seats",
   "exact": "Ø28 × 8",
   "mates": "bearing-6001 outer ring",
   "fit": "press",
   "files": "bearing-cap-"
  },
  {
   "feature": "bearing seats",
   "exact": "Ø28 × 8 (two)",
   "mates": "bearing-6001 outer rings",
   "fit": "press",
   "files": "seal-cap-"
  },
  {
   "feature": "seal housing",
   "exact": "Ø22 × 7",
   "mates": "radial shaft seal 12 × 22 × 7",
   "fit": "press",
   "files": "seal-cap-"
  },
  {
   "feature": "shaft clearance",
   "exact": "Ø14",
   "mates": "Ø12 shaft (no contact)",
   "fit": "designed",
   "files": "all"
  },
  {
   "feature": "bracket holes",
   "exact": "3 × M4 (drawn Ø4 × 10) on r 30",
   "mates": "shcs-m4x12",
   "fit": "designed",
   "files": "seal-cap-"
  },
  {
   "feature": "ports",
   "exact": "3 × 1/4-18 NPT, tap drill Ø11.1 × 11",
   "mates": "fill valve, gauge, relief valve (1/4 NPT male)",
   "fit": "designed",
   "files": "port-cap-"
  }
 ],
 "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": "Where do the fill valve, gauge and relief valve go?",
   "a": "In the 3 in port cap on top of the crankcase cross; the working space follows through the piston's fit."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "bearing-cap-3in-blind-6001",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/htd-crankcase-caps-3in/bearing-cap-3in-blind-6001.step",
   "stl": "https://xemstudio.com/files/hardware/htd-crankcase-caps-3in/bearing-cap-3in-blind-6001.stl",
   "note": "3 in blind bearing cap: ISO 2852 face, Ø76.2 neck to 28, inner boss Ø36 × 20 with a 6001 seat"
  },
  {
   "file": "seal-cap-3in-6001-seal12",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/htd-crankcase-caps-3in/seal-cap-3in-6001-seal12.step",
   "stl": "https://xemstudio.com/files/hardware/htd-crankcase-caps-3in/seal-cap-3in-6001-seal12.stl",
   "note": "3 in seal cap: face, neck to 30, inner boss with a 6001 seat, a second 6001 seat 14..22, 12 × 22 × 7 shaft-seal housing at the outer face, 3 × M4 tapped on r 30"
  },
  {
   "file": "port-cap-3in-3x-npt14",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/htd-crankcase-caps-3in/port-cap-3in-3x-npt14.step",
   "stl": "https://xemstudio.com/files/hardware/htd-crankcase-caps-3in/port-cap-3in-3x-npt14.stl",
   "note": "3 in port cap: neck to 16, three 1/4 NPT ports on r 20 (fill valve, gauge, relief valve)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/htd-crankcase-caps-3in/index.md"
}