The Thor motorcycle was produced by the Aurora Automatic Machinery Company, of Aurora, Illinois, which from October 1902 was contracted to build engines for Indian. The deal permitted Aurora to use the Hedstrom-designed motors in its own models and sell any surplus to other manufacturers, resulting in a rash of new motorcycles that were effectively Indian clones. The Thor-brand engines were identical to those of Indian up to 1907, when the arrangement between the two companies expired and Indian commenced full-time manufacture on its own behalf. Thereafter the two makes gradually diverged and in 1910 Aurora introduced a new "F-head" engine of its own design. This was doubled up in 1911 to make a v-twin - the Model O - which featured mechanical inlet valves, though the single retained the "atmospheric" type for another year or so. Previously, Thor had mounted its v-twin engine with the rear cylinder vertical, but from 1912 onwards adopted the more conventional placement. That same year the twin was extensively redesigned, becoming the Model U, and in 1914 its capacity was increased from 61ci to 76.25ci. The Model U was unquestionably fast: Thor set the fastest 5-mile and 50-mile times on dirt in 1913, and in 1914 Bill Brier finished 2nd on one in the Dodge City 300, then America's most prestigious motorcycle race. Despite the design's promise, Aurora ceased motorcycle production the following year to concentrate on its domestic appliance business. The company still exists today.