This is a single-cylinder four-stroke engine with functional valves. Good for educational purposes or just having a nice toy to play around. The assembly process is simple yet fun with only minimum amount of non-printed parts needed. Please refer assembly drawing for location of parts and the part list. When assembling, make sure to align timing marks in the 3 gears. If not aligned, collision between piston and valves can happen. You can choose between 3 variants of cylinder heads: Without text, with 4-stroke text or with OHC text. All_parts.3mf file contains the print profile for each part and Engine_parts zip folder contains all stl files.

Non-printed parts needed:

-2pcs Compression spring for valves (I used 9.5x19mm): max outside diameter 10mm, min inside diameter 7.5mm. length ideally around 20mm, but not less than 14mm. -2pcs screw for exhaust, M2.5X8.

Tips for smooth functioning:

-Sand down sliding surfaces if needed, especially holes for crank shaft and the shaft for idler gear (see picture) -Add lubricant. Especially valve stems might need it if they stick up too much