{
 "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": "counterweighted-cranks",
 "name": "Counterweighted crank discs, crank webs and bolt-on counterweights",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How do I balance the crank on a small Stirling engine?",
 "tags": [
  "crank",
  "counterweight",
  "balance",
  "crank web",
  "flywheel",
  "stirling",
  "gamma",
  "long earth society"
 ],
 "aliases": [
  "stirling engine counterweight",
  "crank balance small engine",
  "counterweighted crank disc stl",
  "crank web 3d print",
  "how to balance a model engine",
  "bolt on counterweight"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 13,
 "url": "https://xemstudio.com/objects/counterweighted-cranks/",
 "sheet_txt": "https://xemstudio.com/objects/counterweighted-cranks/sheet.txt",
 "sheet": {
  "basis": "Single-cylinder balancing practice: counterweight = all rotating mass + ~50% of the reciprocating mass placed opposite the pin at the pin radius; discs cut away on the pin side and thickened opposite; bolt-on arcs for trimming on the engine",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Why: the piston, con-rod and crank pin all pull outward once per turn; without a counterweight the engine walks across the table and the bearings hammer. Put mass opposite the pin: m_cw × r_cw = m_rotating × r_pin + 0.5 × m_reciprocating × r_pin. Over-balance toward 60–70% if the engine shakes mostly along the cylinder axis.",
   "The discs here remove material beyond the pin and add a 150° thickened sector opposite it (about 50% balance for a printed con-rod + syringe plunger); the bolt-on arcs trim the rest: drill the flywheel rim at the three M3 positions and move the arc until it runs smooth. Crank webs are the bar-crank alternative: two webs + a Ø3 pin make a throw in the middle of a shaft so the con-rod can sit between two bearings.",
   "Check: spin the bare crank on its bearings; it should stop anywhere (static balance). Then run and feel the stands. Running speed of a hobby gamma is 200–600 rpm, so static balance is enough; dynamic balance only matters past ~1500 rpm.",
   "LES: counterweighted discs on the 2 in gamma; bolt-on arcs on the Ø100 flywheel for the final trim."
  ],
  "table": {
   "columns": [
    "stroke_mm",
    "pin_offset_mm",
    "disc_dia_mm",
    "parts"
   ],
   "rows": [
    [
     10,
     5,
     32,
     "disc + web"
    ],
    [
     15,
     7.5,
     32,
     "disc + web"
    ],
    [
     20,
     10,
     34,
     "disc + web"
    ],
    [
     25,
     12.5,
     39,
     "disc + web"
    ],
    [
     30,
     15,
     44,
     "disc + web"
    ]
   ]
  }
 },
 "sheet_text": "Counterweighted crank discs, crank webs and bolt-on counterweights — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/counterweighted-cranks/  (CC BY 4.0)\nBasis: Single-cylinder balancing practice: counterweight = all rotating mass + ~50% of the reciprocating mass placed opposite the pin at the pin radius; discs cut away on the pin side and thickened opposite; bolt-on arcs for trimming on the engine\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Why: the piston, con-rod and crank pin all pull outward once per turn; without a counterweight the engine walks across the table and the bearings hammer. Put mass opposite the pin: m_cw × r_cw = m_rotating × r_pin + 0.5 × m_reciprocating × r_pin. Over-balance toward 60–70% if the engine shakes mostly along the cylinder axis.\n- The discs here remove material beyond the pin and add a 150° thickened sector opposite it (about 50% balance for a printed con-rod + syringe plunger); the bolt-on arcs trim the rest: drill the flywheel rim at the three M3 positions and move the arc until it runs smooth. Crank webs are the bar-crank alternative: two webs + a Ø3 pin make a throw in the middle of a shaft so the con-rod can sit between two bearings.\n- Check: spin the bare crank on its bearings; it should stop anywhere (static balance). Then run and feel the stands. Running speed of a hobby gamma is 200–600 rpm, so static balance is enough; dynamic balance only matters past ~1500 rpm.\n- LES: counterweighted discs on the 2 in gamma; bolt-on arcs on the Ø100 flywheel for the final trim.\n\nstroke_mm  pin_offset_mm  disc_dia_mm  parts\n10  5.0  32  disc + web\n15  7.5  32  disc + web\n20  10.0  34  disc + web\n25  12.5  39  disc + web\n30  15.0  44  disc + web\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Engine balance — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Engine_balance\n- Wikipedia: Crankshaft — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Crankshaft\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, 13 parts): https://xemstudio.com/files/hardware/counterweighted-cranks/index.json\nAPI: https://xemstudio.com/api/geometry?object=counterweighted-cranks\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Engine balance",
   "url": "https://en.wikipedia.org/wiki/Engine_balance",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Crankshaft",
   "url": "https://en.wikipedia.org/wiki/Crankshaft",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "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": [
  "crank-conrod-flywheel-kit",
  "shaft-collars-clips-and-shafts",
  "ball-bearings-metric",
  "dowel-pins-metric",
  "set-screws-metric"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "stirling-linkage-fittings",
     "why": "Ø5 shaft in the 625 crank stands"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "crank-conrod-flywheel-kit",
     "why": "con-rods on the Ø3 pin"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "nut-weighted-flywheels",
     "why": "counterweight with nuts in one half of the flywheel"
    },
    {
     "slug": "crank-conrod-flywheel-kit",
     "why": "plain crank discs"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "stirling-shafts-and-rods",
     "why": "Ø5 D-flat crankshaft"
    },
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 crank pins"
    },
    {
     "slug": "set-screws-metric",
     "why": "M3 grubs"
    }
   ]
  }
 ],
 "faq": [
  {
   "q": "How much counterweight does a single-cylinder engine need?",
   "a": "Mass opposite the pin such that m·r equals the rotating mass plus about half the reciprocating mass at the pin radius; trim on the engine with the bolt-on arcs until the stands stop buzzing."
  },
  {
   "q": "Why does my Stirling engine walk across the table?",
   "a": "Unbalanced crank: the piston and con-rod mass pull outward every turn. Fit a counterweighted disc or add an arc to the flywheel opposite the crank pin."
  },
  {
   "q": "Disc crank or crank web?",
   "a": "A disc is simplest (one part, pin on the face, con-rod outboard). Webs let the con-rod sit between two bearings on a straight shaft: stiffer, better for two-cylinder or beam engines."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "cw-crank-disc-stroke10",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke10.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke10.stl",
   "note": "counterweighted crank disc, 10 mm stroke (pin at 5.0), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "crank-web-stroke10",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke10.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke10.stl",
   "note": "crank web (bar crank) 10 mm stroke, Ø5 bore with set-screw hub, Ø3 pin; two make a full crankshaft throw"
  },
  {
   "file": "cw-crank-disc-stroke15",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke15.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke15.stl",
   "note": "counterweighted crank disc, 15 mm stroke (pin at 7.5), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "crank-web-stroke15",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke15.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke15.stl",
   "note": "crank web (bar crank) 15 mm stroke, Ø5 bore with set-screw hub, Ø3 pin; two make a full crankshaft throw"
  },
  {
   "file": "cw-crank-disc-stroke20",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke20.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke20.stl",
   "note": "counterweighted crank disc, 20 mm stroke (pin at 10.0), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "crank-web-stroke20",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke20.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke20.stl",
   "note": "crank web (bar crank) 20 mm stroke, Ø5 bore with set-screw hub, Ø3 pin; two make a full crankshaft throw"
  },
  {
   "file": "cw-crank-disc-stroke25",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke25.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke25.stl",
   "note": "counterweighted crank disc, 25 mm stroke (pin at 12.5), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "crank-web-stroke25",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke25.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke25.stl",
   "note": "crank web (bar crank) 25 mm stroke, Ø5 bore with set-screw hub, Ø3 pin; two make a full crankshaft throw"
  },
  {
   "file": "cw-crank-disc-stroke30",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke30.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/cw-crank-disc-stroke30.stl",
   "note": "counterweighted crank disc, 30 mm stroke (pin at 15.0), Ø5 bore, M3 grub, mass opposite the pin ≈ 50% of the con-rod+piston at the pin radius"
  },
  {
   "file": "crank-web-stroke30",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke30.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/crank-web-stroke30.stl",
   "note": "crank web (bar crank) 30 mm stroke, Ø5 bore with set-screw hub, Ø3 pin; two make a full crankshaft throw"
  },
  {
   "file": "bolt-on-counterweight-r15",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/bolt-on-counterweight-r15.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/bolt-on-counterweight-r15.stl",
   "note": "bolt-on counterweight arc, outer R30... (R30 OD, 120°), 3 × M3; add to any flywheel or disc opposite the pin"
  },
  {
   "file": "bolt-on-counterweight-r20",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/bolt-on-counterweight-r20.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/bolt-on-counterweight-r20.stl",
   "note": "bolt-on counterweight arc, outer R40... (R40 OD, 120°), 3 × M3; add to any flywheel or disc opposite the pin"
  },
  {
   "file": "bolt-on-counterweight-r25",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/counterweighted-cranks/bolt-on-counterweight-r25.step",
   "stl": "https://xemstudio.com/files/hardware/counterweighted-cranks/bolt-on-counterweight-r25.stl",
   "note": "bolt-on counterweight arc, outer R50... (R50 OD, 120°), 3 × M3; add to any flywheel or disc opposite the pin"
  }
 ],
 "markdown": "https://xemstudio.com/objects/counterweighted-cranks/index.md"
}