Orbatal valve potty three cilinder areal

[bernhard]

I am building this radial engine and I have a question about the thickness of the mentioned valve. On the drawing is noted "adjust thickness to give 0.05mm clearence in available steam chest space" The thickness of the valve is 6.35mm but the thickness of the steam chest is 9.35mm. What to do?
Thx in advance for your reaction.

Ben