GENERAL
The model is designed to be (de)mountable with allen bolts and nuts. As such the finished model is very suitable for educational purposes.


Engine
A Overhead Valves engine is an internal combustion engine with the valves placed in the cylinder head. In this case the valves are operated by rockers and push rods.
This single cylinder engine has two valves, with an engine capacity of 123 cc.

Gearbox
In a constant mesh gearbox all the gears of the main shaft are in constant mesh with the corresponding gears of the countershaft. A sliding dog clutch is provided on the main shaft.
The constant mesh gearbox has forward neutral and reverse gears.

Primary Drive
For the primary drive there are 2 options: by chain (80 parts!) or gears.
Chain tension and gear adjustment can be obtained by sliding the gearbox on the sledge.

Dimensions: 232 x 129 x 255 mm.
Weight: 0.9 kg.


PRINTING
The parts should be printed on a smooth build plate.
Try to avoid elephant foot.

I printed the model with PLA+ filament on a Prusa Mini.
Sliced with PrusaSlicer, 0.15 mm layer height, organic support where needed.
Printing hints are added for most parts.


ASSEMBLY
For assembled and exploded views, see the “3D Views” folder.
Assembly is in alphabetical order (A1 → M2 ).
A small amount of machine oil will help a smooth running of the assembled model.

Valve timing is done by putting the piston in the top position, and at the same time aligning the camshaft pointer with the corresponding pointer on the crankcase.


METAL PARTS
Two coil springs are needed for the valves, 16 mm width x 20mm height. Wire thickness 0.9 or 1.0 mm (AliExpress).

Engine
Nine M6x16 mm allen bolts.
Two M6 nuts.
Four M5x16 mm allen bolts.
Four M5 nuts.
Two M4x12 mm bolts.

Gearbox
Four M6x16 mm allen bolts.
Two M5x16 mm allen bolts.
Two M5 nuts.

Sledge
Eight M6x16 mm allen bolts.

Although metal parts are preferred for strength, you can also use the designs for valve springs and bolts and nuts.