A flathead engine, also known as a sidevalve engine is an internal combustion engine with its valves contained within the engine block, instead of in the cylinder head, as in an overhead valve engine.

Printing and Assembly
The parts should be printed on a smooth build plate, not textured.
If possible, avoid elephant foot.

I printed the model on a PRUSA MINI, with PLA+ filament, layer height 0.15 mm.
I use Hard Plastic Glue where necessary.

For assembled and exploded views, use .stl files 0… 01... 02… 03… (do not print).
Printing and assembly in alphabetical order (A1 → J1).
Printing tips are available for many parts.

Dimensions: 167 x 97 x 129 mm.
Weight: 0.2 kg.

Metal parts
To join the cylinders to the crankcase, eight metal 60 mm M5 threaded rods are needed.
Four coil springs are needed for the valves, 10 mm width x 15 mm height. Wire thickness 0.6 or 0.7 mm (AliExpress).

Constant Mesh Two Speed Gearbox
This engine matches with this gearbox: Constant Mesh Two Speed Gearbox by Bootjevaarder - MakerWorld