# Crankcase insert for a 2 in tri-clamp cross: displacer-rod guide, crank chamber and run filler

> How do I guide a displacer rod and fill the dead volume inside a 2 inch tri-clamp cross?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: ASME BPE 2 in bore Ø47.5; ISO 2852 Type B lip (Ø45.3, 2.8 from the joint plane); slot, chamber and gap sizes are design values from the crank and con-rods
- Page: https://xemstudio.com/objects/tri-clamp-cross-crankcase-insert/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-cross-crankcase-insert · Plain text: https://xemstudio.com/objects/tri-clamp-cross-crankcase-insert/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

- One piece that fills the run of a 2 in cross with the working gas still free to move. It drops in from the top, stands on the lower gasket's lip and passes the lip with a Ø45.3 spigot that ends level with the lip's lower face.
- Lower run: a Ø3 bore 31.55 mm long is the displacer-rod guide (running fit). Above it a column for the displacer's rod clevis and a slab for its con-rod; two Ø8 passages carry the gas from under the insert to the crank chamber; a Ø18 pocket at the bottom takes the displacer cap's boss at the top of its stroke.
- Middle: a Ø29 chamber straight through along the branch axis; the two branch plugs' noses fill its ends up to the crank. Upper run: slab and column for the diaphragm con-rod and clevis, a Ø22 pocket for the centre disc and nuts, and a cone that stays 1 mm under the membrane at full inward travel.
- Fits: Ø47.5 slide in the bore; spigot touches the lip's Ø45.3; Ø3 guide run on the rod. Chamber, slots and the gap under the membrane are designed.

## 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 |
|---|---|---|---|---|
| outside | Ø47.5 | 2 in cross run bore | slide | all |
| spigot | Ø45.3 | Type B gasket lip (ID 45.3) | slide | all |
| displacer-rod guide | Ø3 × 31.55 | Ø3 displacer rod (crankshaft-3x60): runs in it | run | all |
| crank chamber | Ø29 along the branch axis | branch-plug noses; crank sweep R 13 | designed | all |
| con-rod slabs and clevis columns | 7 × 18 and 9 × 18 slabs, 13 × 11 boxes, Ø12 round columns | con-rods and rod clevises in motion | designed | all |
| membrane cone | 1.0 under the membrane at ±6 travel; Ø22 disc pocket | centre disc, nuts and boss at full inward travel | designed | all |
| gas passages | 2 × Ø8 | gas path from the displacer to the crank chamber | designed | all |

## Sizes

| feature | value |
|---|---|
| outside | Ø47.5, -86.95 to 88.25 from the cross centre |
| spigot | Ø45.3 to -92.55 |
| guide | Ø3 × 31.55 |
| crank chamber | Ø29 along X |
| gas passages | 2 × Ø8 |
| gap under the membrane | 1 at ±6 travel |

## Where the files are

- ISO (via iTeh sample): [ISO 2852 clamp liners: face profile and flange / groove diameters](https://cdn.standards.iteh.ai/samples/7850/eb49c396488d408c8ced3e2961d76cf3/ISO-2852-1974.pdf) — PDF — standard excerpt; dimensions are facts
- ASME: [BPE Bioprocessing Equipment (clamp fitting dimensions, tube OD and wall)](https://www.asme.org/codes-standards/find-codes-standards/bpe-bioprocessing-equipment) — standard — ASME; dimensions are facts (verify at link)
- 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/tri-clamp-cross-crankcase-insert/index.json

- crankcase-insert-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cross-crankcase-insert/crankcase-insert-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cross-crankcase-insert/crankcase-insert-2in.stl) — 2 in cross crankcase insert: Ø47.5 from the lower lip (-86.95) to the rim (88.25), Ø45.3 spigot to -92.55 (from the cross centre); Ø29 crank chamber along the branches; Ø3 guide 31.55 long; two Ø8 gas passages; membrane cone 1 under full inward travel

## Questions

**Why fill the cross?**

The open 2 in cross holds about 0.55 L of gas; the engine sweeps about 11 mL. Every bit of unswept gas lowers the pressure swing.

**Where does the gas go?**

Up past the displacer, through the two Ø8 passages and the slots into the crank chamber, and up the diaphragm slot to the membrane.

## Fits with

- [Branch plugs for a 2 in tri-clamp cross crankcase](https://xemstudio.com/objects/tri-clamp-cross-branch-plug/)
- [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/)
- [Sanitary clamp crosses (9MP): ½ to 4 in](https://xemstudio.com/objects/sanitary-clamp-crosses/)
- [Tri-clamp volume fillers: 2 in tee-run plugs and annular sleeves](https://xemstudio.com/objects/tri-clamp-volume-filler/)
- [Build list: Tri-clamp cross diaphragm gamma, 2 in](https://xemstudio.com/objects/list-tri-clamp-cross-diaphragm-gamma/)