Check the left rear dropout for numbers. I have an 1988/89 Mach One, and that's where the numbers are on mine. I think mine starts with M1 1088, which is Mach One, October 1988. I Think the 86-87s should be in the same spot, but I'm not positive. If I'm wrong, someone else here probably can correct me. Or go to bmxmuseum.com. Nice score!