Catalysis of the reaction: S-adenosylmethionine + 7-(aminomethyl)-7-deazaguanosine-tRNA = adenine + methionine + epoxyqueuosine-tRNA. 7-(aminomethyl)-7-deazaguanosine-tRNA is also known as preQ1-tRNA, and epoxyqueuosine-tRNA as oQ-tRNA.