# Flywheel crank: Ø100 nut-pocket flywheel with a 7.5 mm crank pin (15 mm stroke)

> Can a Stirling engine's flywheel carry the crank pin?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: The Ø100 M8 nut-pocket flywheel (tools/gen_shafts_flywheels.py) with one added Ø3 pin hole through the hub at 7.5 from the axis
- Page: https://xemstudio.com/objects/flywheel-crank/ · JSON: https://xemstudio.com/api/geometry?object=flywheel-crank · Plain text: https://xemstudio.com/objects/flywheel-crank/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

- Same wheel as flywheel-100-m8-b3 (12 M8 pockets at R40.5, Ø3 hub with M3 grub), plus a Ø3 hole through the hub at 7.5 from the axis, 90° from the grub, for a dowel-3x16 crank pin (10 in the hub, through a 5 mm con-rod, 1 proud). Overhung at a shaft end with the hub toward the con-rod: on the mug LTD it is the displacer crank (the web on the far side, so the displacer clevis passes under the rim); on the test-tube marble engine it drives the rocking link.
- Six M8 nuts in alternate pockets to start.

## 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 |
|---|---|---|---|---|
| hub bore | Ø3 | Ø3 shaft (crankshaft or dowel-3x30) | slide | all |
| crank-pin hole | Ø3, 7.5 from the axis | dowel-3x16 crank pin | press | all |
| grub hole | Ø2.5 (M3 tapped) | set-m3x8 | designed | all |
| nut pockets | 12 × M8 hex, one flat outward | M8 hex nut (flywheel weight) | press | all |

## Sizes

| feature | value_mm |
|---|---|
| diameter | 100 |
| crank throw | 7.5 |
| pin hole | Ø3 through the 12.3 hub |
| bore | Ø3 |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

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

Index: https://xemstudio.com/files/hardware/flywheel-crank/index.json

- flywheel-crank-100-m8-b3-s15: [STEP](https://xemstudio.com/files/hardware/flywheel-crank/flywheel-crank-100-m8-b3-s15.step) · [STL](https://xemstudio.com/files/hardware/flywheel-crank/flywheel-crank-100-m8-b3-s15.stl) — Ø100 flywheel with 12 M8 nut pockets (the nut-pocket flywheel's geometry, Ø3 hub, M3 grub) and a Ø3 crank-pin hole through the hub 7.5 from the axis (15 mm stroke), 90° from the grub

## Questions

**Why put the crank pin in the flywheel?**

The mug LTD's two cylinders are only 35 mm apart; with both cranks overhung there is no room for a separate flywheel on the shaft, so the flywheel is the displacer crank.

## Fits with

- [Build list: Mug LTD (sits on a coffee mug)](https://xemstudio.com/objects/list-ltd-mug/)
- [LTD Stirling bottom plate, Ø120 and Ø170](https://xemstudio.com/objects/ltd-bottom-plate/)
- [LTD Stirling top plate with syringe socket, Ø120 and Ø170](https://xemstudio.com/objects/ltd-top-plate/)
- [Glass syringes 1–50 mL (all-glass, ground-glass plunger): barrel and plunger](https://xemstudio.com/objects/glass-syringes/)
- [Flywheels Ø100–Ø200 with hex-nut rim pockets](https://xemstudio.com/objects/nut-pocket-flywheels/)
- [Hex nuts M8, M10, M12, 3/8 in and 1/2 in (flywheel weights)](https://xemstudio.com/objects/hex-nut-weights/)