RE: OS TWIN FT 120 GEMINI CAM SETTINGS
When you install the crankshaft and the camshaft, you line up the two timing marks on the gears so that they are together in the middle in a straight line between the centers of both shafts. This will line them up correctly.
To set the tappet clearance, you rotate the engine so that one valve is fully-depressed, and you set the other one. Then, rotate the engine to depress the other valve, and set the one that's not depressed.
You use two feeler gauges to set the clearance: 0.04 mm and 0.1 mm. The thin one will fit and the thick one will not. You can get the tools and feelers from your favorite hobby retailer:
OSMG6334 72200060 GAUGES TOOLS 4-STROKE US$11.99