The 'Big Port' AJS is one of the classic vintage motorcycles. Named Big Port because of the large diameter of its exhaust the 350cc version was hugely successful in competition and was commoner than the 500 back in the day as now.
The 500cc Big Port (official model name G8) was never so succesful on the track and, though sold as a sporting model, was obviously less focussed that the 350. The G8 wore touring mudguards whilst the 350cc 'H6' carried skimpy little numbers.
|c1926 AJS 500cc Big Port G8.|
Postscript: Thanks to Geert de Boer from Netherlands for pointing out that really it was only the 350 that was commonly called the 'Big Port' back in the day, the 500 wasn't popularly known as such. It also seems that I have got in a muddle over AJS model numbers - G prefix models were from 1926 and H from 1927, the 6 suffix bikes were the 350ohv and 8 suffix 500ohv. The particular bike in the photo above is a H8 from 1927 - 1927 being the first year in which the model was fitted with wired-on tyres.
Many thanks Geert for putting the record straight, when these things are out in the public domain and used as reference it is always nice to get the details fully correct.