Pictures are really needed since this is likely before known Schwinn serials date back to. I'm expecting this would be from the 28" motobike days as there is no letter preceding it? I have a mid-20s ish Schwinn with the serial of 454228. You might have the best luck to hope that you have the original crank with a date stamp in the center. Mine has a '37 crank in it so I wasn't so lucky.