# Alpha V-twin crank disc Ø26, one pin, 16 mm stroke

> What crank disc does a 90° V-twin alpha Stirling use?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: 90° V alpha: both con-rods on one pin; throw 8 (stroke 16)
- Page: https://xemstudio.com/objects/alpha-v-twin-crank-disc/ · JSON: https://xemstudio.com/api/geometry?object=alpha-v-twin-crank-disc · Plain text: https://xemstudio.com/objects/alpha-v-twin-crank-disc/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

- Ø26 × 6 disc with a Ø5 bore (fit: slide) and a Ø2.5 radial hole (M3 tap size) for the grub screw.
- ONE Ø3 hole (fit: press) at 8 mm for a Ø3 × 20 crank pin; both con-rods ride it, one plane each, with 1 mm spacers and a 3 mm collar on the end.
- A two-pin disc with pins 90° apart under a 90° V would give 0° or 180° and the engine would not run; that disc is for parallel cylinders.

## 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 |
|---|---|---|---|---|
| crank-disc bore | Ø5 | Ø5 crankshaft (M3 grub) | slide | alpha-crank-disc-* |
| crank-disc pin hole | Ø3 | Ø3 × 20 crank pin | press | alpha-crank-disc-* |
| crank-disc grub hole | Ø2.5 | M3 tap drill | designed | alpha-crank-disc-* |

## Sizes

| parameter | value |
|---|---|
| disc | Ø26 × 6 |
| bore | Ø5 |
| throw | 8 |
| stroke | 16 |
| pin hole | 1 × Ø3 |
| grub hole | Ø2.5 |

## Where the files are

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

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

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

- alpha-crank-disc-s16: [STEP](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.step) · [STL](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.stl) — crank disc Ø26 × 6, Ø5 bore, Ø2.5 tap-drill hole for an M3 grub, ONE Ø3 pin at 8 mm (stroke 16): both con-rods share it

## How it fits

### Goes in or on
- [Alpha V-twin frame for two 10 mL syringes at 90°](https://xemstudio.com/objects/alpha-v-twin-syringe-frame/): on the shaft beside the boss

### Connects to
- [Con-rods with Ø3 pin ends, 45 and 60 mm, 8 × 5](https://xemstudio.com/objects/pin-end-con-rods/): both alpha-conrod-60s on the one Ø3 pin
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/): Ø5 × 80 crankshaft, Ø3 × 20 pin

### Alternatives
- [Two-pin crank disc, pins 90° apart, 6 / 8 / 10 mm throw](https://xemstudio.com/objects/two-pin-crank-disc-90/): for parallel cylinders

## Questions

**Does a V-twin alpha need two crank pins?**

No. In a 90° V both rods share one pin; the V gives the 90° phase.

**What stroke does the alpha crank disc give?**

16 mm (pin at 8 mm), about 2.6 mL per 10 mL syringe.

## Fits with

- [Alpha V-twin frame for two 10 mL syringes at 90°](https://xemstudio.com/objects/alpha-v-twin-syringe-frame/)
- [Con-rods with Ø3 pin ends, 45 and 60 mm, 8 × 5](https://xemstudio.com/objects/pin-end-con-rods/)
- [Two-pin crank disc, pins 90° apart, 6 / 8 / 10 mm throw](https://xemstudio.com/objects/two-pin-crank-disc-90/)
- [Build list: Alpha V-twin, two 10 mL syringes](https://xemstudio.com/objects/list-alpha-v-twin-syringe/)