|A c.1910 Thor-engined Minneapolis board track racer|
|Company founder and chief engineer Joe (Jack) Michaelson c.1910, on a Thor-engined single-speed board track racer with a reduction gear on the crankshaft|
The Michaelson brothers also purchased V-twin engines from the Aurora Automatic Machinery Co. (Thor), another bedrock of the American motorcycle industry. Aurora had been building Oscar Hedstrom's Indian engine design since 1901, since his partner George Hendee, who'd been building bicycles since 1889, didn't have the general engineering facilities required to cast and machine motors. Hendee had all the facilities to build the heavy-duty bicycle chassis, but Aurora built their engines through 1907, after which Indian took over all its own production. Part of Aurora's deal with Indian was licensed production of the Hedstrom motor, an F-head (inlet over exhaust) with 'atmospheric' intake valves, in single and twin-cylinder form, which they sold as their own 'Thor' brand, and also found their way into Merkel, Racycle, Reading Standard, and many other makes, each of which contributed to Indian's (and Aurora's) profits.
|R.S. Porter on another Thor-engined twin-cylinder racer in 1910|
Paul Koutowski won that Indy race on a Minneapolis v-twin with Thor engine, which used a two-speed rear hub - a truly historic occasion, although motorcycle racing at Indy is largely forgotten today: the motorcycle races preceded automobile racing on the track by a year, and the rough original surface led to two crashes in the two-wheel race (one of whom was Jake DeRosier), and two fatalities in the first car race. The surface was repaved with bricks in 1911, and the 'Brickyard' was born...with no more bikes until 2009, when world champ Nicky Hayden pottered around on a vintage Indian.
|Winner of the first (and last, for a Century) motorcycle race at Indianapolis Motor Speedway, one of four held that day|
|William Ottoway's racing influence is clear with these Thor-engined Minneapolis single- and twin-cylinder racers|
|The first Michaelson-designed motor, a sidevalve of 600cc, was among the first to use this configuration in the industry. Note the leading-link forks, which were also a Michaelson Bros design|
|The Minneapolis patented two-speed countershaft gearbox, incorporated in unit with the single-cylinder machines, and as a bolted-on attachment to the Spacke v-twins|
|A 1913 Minneapolis v-twin with Spacke engine and two-speed gearbox|
|The Minneapolis was rare among all motorcycle manufacturers to feature the 'timing' side of the engine on the left. Spacke appears to have specially cast its crankcases to suit the reversed Minneapolis engine|
|The 1911 Minneapolis 'Big 5' single-cylinder|
|It appears a Minneapolis sidevalve single was used in a round-the-world trip covering 65,000 miles in 1911, by Murry Humphries and his wife.|
|Anton Michaelson branched out into tri-car manufacture in 1913/4|
|A 1911 sidevalve Michaelson single, with separate countershaft gearbox|