Moped Army

Ok so I got got my Airsal kit on and was wondering, how does the head seal on tight enough to hold compression without using any gasket? And I was also wondering, when my revival was new the engine made a knocking noise, most noticable at idle. Even after I installed the airsal kit, it still knocks at idle. I am hoping this knocking noise is normal? If I heard this noise on a car I would be worried...