S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the N(7) position of a guanine in 18S rRNA. Important for biogenesis end export of the 40S ribosomal subunit independent on its methyltransferase activity (By similarity). a guanosine in 18S rRNA + S-adenosyl-L-methionine = an N(7)-methylguanosine in 18S rRNA + S-adenosyl-L-homocysteine Belongs to the class I-like SAM-binding methyltransferase superfamily. BUD23/WBSCR22 family.