Counterweighted crank discs, Ø5 bore, 10 to 30 mm stroke — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/counterweighted-crank-discs/  (CC BY 4.0)
Basis: Crank disc ending just past the pin and thickened opposite it; pin at stroke / 2, Ø5 bore, M3 grub
Catalog version: 2026-10-20

Sizes: see table below
- A 6 mm disc (Ø32, 32, 34, 39, 44 for 10–30 mm stroke) with the Ø3 pin hole at half the stroke. On the pin side the disc ends 6 mm past the pin centre, with a Ø10 boss round the pin.
- Opposite the pin a raised segment 4.8 thick (10.8 overall) carries the counterweight; the description sizes it at about 50 % of a con-rod and piston at the pin radius.
- Ø5 bore and a radial Ø2.5 hole (M3 tap drill) at mid-thickness for a grub on the shaft's flat.
- Balance condition: m_cw × r_cw = m_rotating × r_pin + 0.5 × m_reciprocating × r_pin. A crank that stops at any angle when spun bare is statically balanced; at 200–600 rpm that is enough.

file  stroke  pin offset  disc Ø  thickness  envelope
cw-crank-disc-stroke10  10  5.0  32  6 / 10.8  27 × 32
cw-crank-disc-stroke15  15  7.5  32  6 / 10.8  29.5 × 32
cw-crank-disc-stroke20  20  10.0  34  6 / 10.8  33 × 34
cw-crank-disc-stroke25  25  12.5  39  6 / 10.8  38 × 39
cw-crank-disc-stroke30  30  15.0  44  6 / 10.8  43 × 44

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Engine balance — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Engine_balance
- Wikipedia: Crankshaft — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Crankshaft
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 5 parts): https://xemstudio.com/files/hardware/counterweighted-crank-discs/index.json
API: https://xemstudio.com/api/geometry?object=counterweighted-crank-discs