Looking on the OS Engines, stumbled upon the news of a new Shimo edition of his engine. Still 9 ports but not so much information about it. They talk about new process for piston and... seems they put some shims to move the sleeve height and change the timing.

Wondering what differences among the visible ones (different cooling head - smaller, different color). Crankcase looks like the same as 2106 but without the manual and the parts list for the engine is somewhat difficult to see what's different.

https://www.os-engines.co.jp/osspeed...oad/1fg01.html

Edit: Forgot to include the link.