The thud of an AJS K9 Vintage Motorcycle

The thud of a 1928 500cc AJS model K9 side-valve.
1928 was the final year before AJS moved to the more popular and fashionable (at the time!) saddle tank design. Side valve machines were starting to be phased out by many manufacturers in the late 1920s, in exchange for the sportier, faster, and higher revving overhead valve engines; and for this reason, big side valve singles of this era are somewhat of a rarity these days (particularly for AJS who produced the much desired 350cc OHV big port which underpinned the firms racing success).
The reliability and usability of the side valve motors, however, kept these machines in catalogues for years to come. The 500cc side-valve in particular offered a broad top-gear performance range and an impressive load-carrying ability; this appealed to commercial carriers and private enthusiasts, especially when coupled to one of the firm’s own sidecars.