Thanks M7H for the help I took the head off and measured both the piston to top of cylider and the depth of the button.
The piston to top of cylinder is 3.33mm and the button was 3.14 to equal a .19 clearance so I will need a .31 shim to be at .5.
As you can see the button on my Picco is 3.33 not the .4-.6 you descibed not sure why.
But thanks again.
\

-----

>
Mugen MRX4X - Picco P9 EVO