# Power cylinder liners, piston blanks, crosshead and guide (the non-syringe power piston)

> How do I make a power piston and cylinder for a Stirling engine without a syringe?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Trunk piston and crosshead practice for model engines: clearance-seal piston lapped into a honed liner (10–25 µm radial), or a graphite piston in a glass tube; crosshead takes the con-rod side load so the piston only moves axially
- Page: https://xemstudio.com/objects/power-cylinder-piston-crosshead/ · JSON: https://xemstudio.com/api/geometry?object=power-cylinder-piston-crosshead · Plain text: https://xemstudio.com/objects/power-cylinder-piston-crosshead/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Two ways to seal: (1) lapped fit: brass or aluminium piston turned 0.05 under, lapped with fine compound into a honed brass/stainless liner until it falls through slowly under its own weight; (2) graphite piston in a borosilicate glass tube (16 or 20 mm test tube / tube): self-lubricating, near-zero friction, the premium option. Printed liners and pistons here are for prototyping the layout; a printed piston will not seal.
- Sizes: Ø16 (1.65 mL per 12 mm stroke... see table), Ø20, Ø25, Ø30. For the 2 in tri-clamp gamma with the Ø46 × 90 displacer at 20 mm stroke, a Ø20 × 12 mm stroke piston (3.8 mL) is in the right range; Ø16 at 15 mm for the 1.5 in.
- Crosshead: a Ø8 slider on the Ø3 piston rod running in a guide bushing; the con-rod's angle pushes sideways on the crosshead, not the piston, so the lapped seal stays round. Trunk alternative: wrist pin in the piston boss, con-rod directly on it; fine for short rods (L ≥ 4 × stroke).
- Flange: 4 × M3 on a Ø(D + 16) circle, matches the power head's socket pattern when drilled; seal with a paper or silicone gasket.

## Sizes

| bore_mm | liner_len_mm | piston_len_mm | ml_per_12mm_stroke |
|---|---|---|---|
| 16 | 40 | 14 | 2.41 |
| 20 | 45 | 18 | 3.77 |
| 25 | 50 | 22 | 5.89 |
| 30 | 55 | 27 | 8.48 |

## Where the files are

- Wikipedia: [Crosshead](https://en.wikipedia.org/wiki/Crosshead) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Piston](https://en.wikipedia.org/wiki/Piston) — web — CC BY-SA 4.0 (text)
- James R. Senft: [Miniature Stirling engine piston fits (LTD book)](https://www.stirlingengine.com/) — book — reference (verify at link)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (11 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/index.json

- liner-16x40-flanged: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-16x40-flanged.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-16x40-flanged.stl) — power cylinder liner Ø16 bore × 40, 3 wall, 4 × M3 flange (print to prototype; real liner = honed brass/stainless tube or a glass tube)
- piston-16x14-blank: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-16x14-blank.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-16x14-blank.stl) — piston blank Ø15.9 × 14: lap to fit; Ø3 rod boss and a Ø3 wrist-pin boss
- liner-20x45-flanged: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-20x45-flanged.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-20x45-flanged.stl) — power cylinder liner Ø20 bore × 45, 3 wall, 4 × M3 flange (print to prototype; real liner = honed brass/stainless tube or a glass tube)
- piston-20x18-blank: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-20x18-blank.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-20x18-blank.stl) — piston blank Ø19.9 × 18: lap to fit; Ø3 rod boss and a Ø3 wrist-pin boss
- liner-25x50-flanged: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-25x50-flanged.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-25x50-flanged.stl) — power cylinder liner Ø25 bore × 50, 3 wall, 4 × M3 flange (print to prototype; real liner = honed brass/stainless tube or a glass tube)
- piston-25x22-blank: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-25x22-blank.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-25x22-blank.stl) — piston blank Ø24.9 × 22: lap to fit; Ø3 rod boss and a Ø3 wrist-pin boss
- liner-30x55-flanged: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-30x55-flanged.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/liner-30x55-flanged.stl) — power cylinder liner Ø30 bore × 55, 3 wall, 4 × M3 flange (print to prototype; real liner = honed brass/stainless tube or a glass tube)
- piston-30x27-blank: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-30x27-blank.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-30x27-blank.stl) — piston blank Ø29.9 × 27: lap to fit; Ø3 rod boss and a Ø3 wrist-pin boss
- crosshead-8mm-rod3: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/crosshead-8mm-rod3.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/crosshead-8mm-rod3.stl) — crosshead: Ø8 slider on a Ø3 piston rod with a clevis for the con-rod (keeps side load off the piston)
- crosshead-guide-8mm: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/crosshead-guide-8mm.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/crosshead-guide-8mm.stl) — crosshead guide: Ø8.15 bore × 30, flange with 2 × M3 (or press a 8 × 12 bushing in)
- wrist-pin-3x16: [STEP](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/wrist-pin-3x16.step) · [STL](https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/wrist-pin-3x16.stl) — Ø3 × 16 wrist pin (dowel) for the piston boss

## How it fits

### Goes in or on
- [Gamma frame: base plates for tri-clamp engines, rocker beam and pivot post](https://xemstudio.com/objects/gamma-base-plate-and-beam/): liner on the base plate

### Connects to
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/): con-rod to the crosshead clevis

### Alternatives
- [Tri-clamp power pistons and crank linkage: full-bore ring-less pistons, con-rods, crank webs and a clamp-on crank frame for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-power-pistons/): full-bore piston in the spool itself
- [Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels](https://xemstudio.com/objects/syringe-pistons/): syringe barrel as the cylinder
- [Free-piston Stirling core: displacer, power piston, liner, gas spring, stops, clearance-seal and tuning tables](https://xemstudio.com/objects/free-piston-core/): Ø30 / Ø40 piston blanks

### Also needed
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/): Ø3 wrist pin
- [Hobby brass tube (K&S), 1/16–21/32 in and 1–12 mm, telescoping](https://xemstudio.com/objects/brass-tube-ks/): or a glass / brass tube as a real liner

## Questions

**What is the best power piston for a hobby Stirling engine?**

A graphite piston in a borosilicate glass tube: no lubrication, near-zero friction, good seal. Next best: a lapped brass piston in a brass liner. A syringe is the quick version.

**How tight should a Stirling piston fit?**

Clearance seal: 10–25 µm radial. Test: the piston should slide slowly through the liner under its own weight with the far end closed by a finger, and stop when it is uncovered.

**Why use a crosshead?**

It takes the con-rod's sideways push so the piston sees only axial motion: the lapped fit stays round and friction stays low. Use one whenever the con-rod is short or the piston is lapped.

## Fits with

- [Plastic syringes 1–60 mL as pistons and cylinders](https://xemstudio.com/objects/plastic-syringes/)
- [Borosilicate test tubes, 10×75 to 30×200 mm](https://xemstudio.com/objects/borosilicate-test-tubes/)
- [Free-piston Stirling core: displacer, power piston, liner, gas spring, stops, clearance-seal and tuning tables](https://xemstudio.com/objects/free-piston-core/)
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/)
- [Bearing housings and linear supports: KP08, KFL08, SK8, SC8UU, V-wheels, sleeve bushings](https://xemstudio.com/objects/bearing-housings-and-rod-supports/)
- [Tri-clamp displacers and engine heads: 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacers-and-heads/)