A few evocative shots of a vintage BSA combo. I believe it is a S29-18 from 1929 though am happy for any experts out there to correct me!
BSA Models numbers of the late vintage / early post vintage era are slightly confusing as they are alpha numeric and the same model number prefix applies to multiple different models - ie S29 designates that it is a 500cc model from 1929 (in 1930 it was the S30). Bikes usually get identified with the prefix only but it is the suffix that gives the true id. So, for example an S29 could be any bike in the 1929 range that was 500cc, the '-18' suffix means that it was the upright-engined side-valve model (also known at the 4.93hp Light).
For more details on 1930s Beesas take a look at this site: https://www.bsa1930s.nl/