# Tri-clamp crank head: ISO 2852 cap with Ø3 rod bore and two 623 towers, 1.5, 2 and 3 in

> What tri-clamp head carries the displacer rod and a crankshaft on the cap itself?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: ISO 2852 cap face; Ø3 run bore for the displacer rod; two 623 bearing pockets (Ø10) on a Ø3 crank axis 30 mm above the face
- Page: https://xemstudio.com/objects/tri-clamp-crank-head/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-crank-head · Plain text: https://xemstudio.com/objects/tri-clamp-crank-head/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- An ISO 2852 end cap that carries both the displacer rod and a small crankshaft, so the drive sits right on the cylinder.
- On centre: a Ø18 × 9 boss with a Ø3 bore straight through for the Ø3 displacer rod (run fit); the bore is the rod guide and the clearance seal.
- Two towers 10 × 14 × 28 mm stand on the back of the 6 mm cap, centred ±(C3/2 − 11) from the axis (±14.25 / ±21.0 / ±34.5 mm for 1.5 / 2 / 3 in), each with a Ø10 pocket for a 623 bearing; the Ø3 crankshaft axis is 30 mm above the face, 24 mm above the cap's back.
- The overall height is 34 mm; flange Ø50.5 / 64.0 / 91.0.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| bearing pockets | Ø10 | 623 bearing | press | head-crank-* |
| head faces | ISO 2852 | ferrule face + Type B gasket | clamp | head-* |
| rod-gland bore | Ø3 × 13.4 (through cap and Ø18 boss) | Ø3 displacer rod | run | head-crank-* |

## Sizes

| size_in | flange_od_mm | rod_bore_mm | tower_centres_mm | bearing | crank_axis_above_face_mm |
|---|---|---|---|---|---|
| 1.5 | 50.5 | 3 | 28.5 | 623 (Ø10) | 30 |
| 2 | 64.0 | 3 | 42.0 | 623 (Ø10) | 30 |
| 3 | 91.0 | 3 | 69.0 | 623 (Ø10) | 30 |

## Where the files are

- Long Earth Society: [Tri-clamp Stirling engine builds](https://longearthsociety.com/engineering/) — web, video — LES site
- James R. Senft: [An Introduction to Low Temperature Differential Stirling Engines (displacer and gap design)](https://www.stirlingengine.com/) — book — Moriya Press (verify at link)
- Wikipedia: [Stirling engine](https://en.wikipedia.org/wiki/Stirling_engine) — web — CC BY-SA 4.0 (text)

## Free STEP/STL (3 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-crank-head/index.json

- head-crank-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-crank-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-crank-1.5in.stl) — 1.5 in ISO 2852 cap: clearance-seal rod gland (Ø3 bore straight through the cap and its Ø18 boss, 13.4 mm long, for the Ø3 rod; no O-ring) and two 623 bearing towers for a Ø3 crankshaft 24 mm above the cap
- head-crank-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-crank-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-crank-2in.stl) — 2 in ISO 2852 cap: clearance-seal rod gland (Ø3 bore straight through the cap and its Ø18 boss, 13.4 mm long, for the Ø3 rod; no O-ring) and two 623 bearing towers for a Ø3 crankshaft 24 mm above the cap
- head-crank-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-crank-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-crank-3in.stl) — 3 in ISO 2852 cap: clearance-seal rod gland (Ø3 bore straight through the cap and its Ø18 boss, 13.4 mm long, for the Ø3 rod; no O-ring) and two 623 bearing towers for a Ø3 crankshaft 24 mm above the cap

## How it fits

### Goes in or on
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/): ISO 2852 face on the cold-end ferrule

### Connects to
- [Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacer/): Ø3 rod through the Ø3 bore
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/): 623 (3 × 10 × 4) in each Ø10 pocket
- [Rod clevises for a Ø2 or Ø3 rod or a Ø5 tube, 5 mm gap](https://xemstudio.com/objects/rod-clevises/): Ø3-bore crank discs and rod clevis on the Ø3 shaft and rod

### Also needed
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/): Ø3 crankshaft and Ø3 displacer rod
- [Tri-clamp clamp, two-bolt: every flange size ½ to 4 in](https://xemstudio.com/objects/tri-clamp-clamps/): clamp and gasket on the face

## Questions

**How do I seal the displacer rod through a tri-clamp cap?**

With a clearance seal: the crank head has a Ø3 bore straight through its Ø18 × 9 boss, and the Ø3 rod runs in it with no O-ring.

**How high is the crankshaft on the crank head?**

The Ø3 crank axis is 30 mm above the sealing face (24 mm above the cap's back), in two 623 bearings.

**How far apart are the crank-head towers?**

28.5 mm centre to centre on 1.5 in, 42.0 on 2 in, 69.0 on 3 in.

## Fits with

- [Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacer/)
- [Tri-clamp regenerative displacer: Ø31.8, Ø44.5 and Ø69.9 with 12 slots, 1.5 mm gap](https://xemstudio.com/objects/tri-clamp-regenerative-displacer/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [Rod clevises for a Ø2 or Ø3 rod or a Ø5 tube, 5 mm gap](https://xemstudio.com/objects/rod-clevises/)
- [Crank discs for a Ø5 shaft, 10 to 30 mm stroke](https://xemstudio.com/objects/crank-discs-5mm-bore/)
- [Tri-clamp clamp, two-bolt: every flange size ½ to 4 in](https://xemstudio.com/objects/tri-clamp-clamps/)