# Crankcase flywheels: Ø44 × 12 disc and Ø42 pocket flywheel on a Ø3 shaft, inside a 2 in tri-clamp fitting

> Where does the flywheel go on a Stirling engine with no shaft out of its crankcase?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Design values: Ø44 so the disc turns inside the 2 in bore (Ø47.5); Ø42 so the pocket flywheel turns in the bearing plate's Ø44 pocket inside the gasket lip (Ø45.3); inertia and the cycle's energy swing from the Schmidt estimate
- Page: https://xemstudio.com/objects/tri-clamp-crankcase-flywheel/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-crankcase-flywheel · Plain text: https://xemstudio.com/objects/tri-clamp-crankcase-flywheel/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**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

- Discs on the crankshaft between the crank and the bearing plates' spigots (one on +X, one on −X beside the crank gear), and a pocket flywheel on each shaft end in the bearing plate's pocket, 0.5 mm from the end cap. An M3 grub holds each.
- Why: nothing turns outside the vessel, so these, the crank gear and the generator's can (which turns 2.8 times faster, so counts 7.8 times its own inertia) are the whole flywheel. One cycle swings about 0.16 J against a steady load: a speed swing of 12–27 % at 900 rpm and 7–15 % at 1200 rpm for a disc density of 7.8 to 2.7 g/cm³ (the motor's turning part taken as 18 g at r 12.5).

## 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 |
|---|---|---|---|---|
| bore | Ø3 | Ø3 crankshaft (M3 grub) | slide | all |
| grub hole | Ø2.5 (M3 tapped), radial from the rim | set-m3x10 | designed | crank-flywheel-* |
| grub hole | Ø2.5 (M3 tapped) in the hub | set-m3x3 | designed | pocket-flywheel-* |
| rim | Ø44 / Ø42 | 2 in bore Ø47.5 / plate pocket Ø44 and gasket lip Ø45.3 (no contact) | designed | all |

## Sizes

| file | size | bore | per engine |
|---|---|---|---|
| crank-flywheel-44x12-b3 | Ø44 × 12 | Ø3, radial M3 grub | 2 |
| pocket-flywheel-42x8-b3 | Ø42 × 8 + Ø10 hub | Ø3, M3 grub | 2 |

## Where the files are

- Ohio University (I. Urieli): [Stirling cycle machine analysis: the Schmidt (isothermal) analysis](https://www.ohio.edu/mechanical/stirling/isothermal/Schmidt.html) — web — university course pages (verify at link)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/index.json

- crank-flywheel-44x12-b3: [STEP](https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/crank-flywheel-44x12-b3.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/crank-flywheel-44x12-b3.stl) — crankcase flywheel disc Ø44 × 12, Ø3 bore, radial M3 tapped hole (Ø2.5) from the rim to the bore at mid-thickness
- pocket-flywheel-42x8-b3: [STEP](https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/pocket-flywheel-42x8-b3.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-crankcase-flywheel/pocket-flywheel-42x8-b3.stl) — pocket flywheel Ø42 × 8 on a Ø10 × 12.9 hub, Ø3 bore, M3 grub hole (Ø2.5) in the hub: turns in the bearing plate's Ø44 pocket

## Questions

**Why is the flywheel inside?**

Nothing turns outside the vessel: the discs, the pocket flywheels, the crank gear and the generator's can are the whole flywheel.

## Fits with

- [Step-up gears for a generator inside a 2 in tri-clamp cross: 42 : 15, module 1](https://xemstudio.com/objects/tri-clamp-generator-step-up-gears/)
- [Clamp-in bearing plate: 2 in, two ISO 2852 faces, spigot with two 623 seats](https://xemstudio.com/objects/tri-clamp-clamp-in-bearing-plate/)
- [Inner crank webs for the tri-clamp cross gamma: two throws 90° apart on a Ø3 shaft](https://xemstudio.com/objects/tri-clamp-cross-crank-webs/)
- [Build list: Tri-clamp sealed diaphragm generator, 2 in](https://xemstudio.com/objects/list-tri-clamp-sealed-diaphragm-generator/)