# Alpha V-twin: 90° two-pin crank discs, V block, transfer tee

> How do I set the 90 degree phase on an alpha Stirling engine?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Alpha configuration: two pistons in separate hot and cold cylinders, 90° apart in phase; here with one crank disc carrying both pins 90° apart (V-twin) or two discs clocked on one shaft
- Page: https://xemstudio.com/objects/alpha-twin-crank-90/ · JSON: https://xemstudio.com/api/geometry?object=alpha-twin-crank-90 · Plain text: https://xemstudio.com/objects/alpha-twin-crank-90/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Alpha phase: the cold piston follows the hot piston by 90°. Simplest way: one crank disc with two pins 90° apart, cylinders in a 90° V over it (V-twin); both con-rods ride the same disc, each pin at the same throw e. Or two separate crank discs on one shaft, clocked 90° with set screws.
- V block: two 10 mL syringe barrels at 90° over the shaft; the hot barrel is glass if you have it (a plastic syringe survives a tea-light hot end at 80 °C only with the heat going into a copper tube, not the barrel). Transfer tee: 4 mm bores, hot → regenerator → cold.
- Strokes 12–20 mm (e 6–10) suit 10 mL syringes (Ø14.5: 1.65 mL per 10 mm). Alpha engines have the highest specific power of the three but need the piston seal on the hot side; the Ross yoke kit is the parallel-cylinder alternative.

## Sizes

| part | size | note |
|---|---|---|
| crank disc 2-pin | e 6 / 8 / 10 | pins 90° apart |
| V block | 2 × Ø16.05 @ 90° | 10 mL syringes |
| transfer tee | 4 mm | regenerator between |

## Where the files are

- Wikipedia: [Stirling engine](https://en.wikipedia.org/wiki/Stirling_engine) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (5 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/alpha-twin-crank-90/index.json

- crank-disc-2pin-90deg-e6: [STEP](https://xemstudio.com/files/hardware/alpha-twin-crank-90/crank-disc-2pin-90deg-e6.step) · [STL](https://xemstudio.com/files/hardware/alpha-twin-crank-90/crank-disc-2pin-90deg-e6.stl) — single crank disc with two Ø3 pin holes 90° apart at 6 mm (stroke 12): both alpha con-rods on one disc
- crank-disc-2pin-90deg-e8: [STEP](https://xemstudio.com/files/hardware/alpha-twin-crank-90/crank-disc-2pin-90deg-e8.step) · [STL](https://xemstudio.com/files/hardware/alpha-twin-crank-90/crank-disc-2pin-90deg-e8.stl) — single crank disc with two Ø3 pin holes 90° apart at 8 mm (stroke 16): both alpha con-rods on one disc
- crank-disc-2pin-90deg-e10: [STEP](https://xemstudio.com/files/hardware/alpha-twin-crank-90/crank-disc-2pin-90deg-e10.step) · [STL](https://xemstudio.com/files/hardware/alpha-twin-crank-90/crank-disc-2pin-90deg-e10.stl) — single crank disc with two Ø3 pin holes 90° apart at 10 mm (stroke 20): both alpha con-rods on one disc
- v-block-90-2x-syringe-10ml: [STEP](https://xemstudio.com/files/hardware/alpha-twin-crank-90/v-block-90-2x-syringe-10ml.step) · [STL](https://xemstudio.com/files/hardware/alpha-twin-crank-90/v-block-90-2x-syringe-10ml.stl) — 90° V block for two 10 mL syringe barrels over one crank (alpha V-twin): bores meet 12 mm above the base
- transfer-tee-4mm: [STEP](https://xemstudio.com/files/hardware/alpha-twin-crank-90/transfer-tee-4mm.step) · [STL](https://xemstudio.com/files/hardware/alpha-twin-crank-90/transfer-tee-4mm.stl) — 4 mm transfer tee (hot cylinder → regenerator → cold cylinder)

## How it fits

### Goes in or on
- [Plastic syringes 1–60 mL as pistons and cylinders](https://xemstudio.com/objects/plastic-syringes/): 10 mL barrels in the V-block

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

### Alternatives
- [Ross yoke kit (alpha Stirling with parallel cylinders)](https://xemstudio.com/objects/ross-yoke-kit/): parallel cylinders
- [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/): two tri-clamp cups as the cylinders

### Also needed
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/): Ø3 crank pin

## Questions

**What phase angle does an alpha Stirling use?**

90°: the cold piston lags the hot piston by a quarter turn. One disc with two pins 90° apart (and cylinders in a 90° V) gives it automatically.

**Which alpha cylinder gets the heat?**

The one whose piston leads: expansion space hot, compression space cold; gas flows through the regenerator between them.

## Fits with

- [Ross yoke kit (alpha Stirling with parallel cylinders)](https://xemstudio.com/objects/ross-yoke-kit/)
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/)
- [Plastic syringes 1–60 mL as pistons and cylinders](https://xemstudio.com/objects/plastic-syringes/)
- [Regenerator and heat materials: stainless mesh counts, steel wool, scrubbers, mica, fiberglass, ceramic, firebrick](https://xemstudio.com/objects/regenerator-and-heat-materials/)
- [Stirling engine configurations: which type needs which parts on this shelf](https://xemstudio.com/objects/stirling-configurations-guide/)