501X/DB01R dampers

[muratti]

Hi,

I just built my new DB01R buggy and for the first time i built dampers without a cap (diaphragma) at the top of the cylinder. The manual says you have to fill oil until 1mm to the top. I rated that or is there a simple way to measure that? When taking too much oil it seems the piston isn´t able to fully compensate and if you fill in not enough and fully press the piston it sounds as if there are air bubbles inside.
Did i build something wrong? Any help would be much appreciated. I have been building many many dampers over the years but never without a cap.

Thanks in advance!