1913 Thor Model U: Early American Twin

Mulholland joined the Navy, became an aircraft maintenance tech, and befriended Ray Paxson (a career Navy noncommissioned officer and fellow motorcycle enthusiast). After the Navy, Mulholland moved to Phoenix and in 1957 he sold the Thor to Paxson. Mulholland regretted that decision almost immediately, and he tried to buy the Thor back from Paxson for the next 32 years. During that more than three decade span, the Thor literally became a barn bike (Paxson stored it in a Montana barn; he didn’t get it running, either). Mulholland enjoyed a career in the aerospace industry and pursued his sports car and motorcycle interests, displaying and riding his motorcycles at vintage events. Mulholland restored and sold a 1926 Harley-Davidson single and a 1913 original paint Indian twin; both now reside in Arizona’s Buddy Stubbs Museum. But Mulholland never forgot the Thor stored in Paxson’s barn. When Paxson passed away in 1989, Mulholland was finally able to resume ownership, purchasing the Thor from Paxson’s family (this time for $8,800, a bit more than the $40 he paid O’Leary in 1947).

After reacquiring the Thor, Mulholland embarked on a mission to resurrect it. His objective was to return the machine to running, original condition. Ever the engineer and enthusiast, Mulholland left notes, correspondence, and drawings, frequently noting that he was “not restoring, only repairing.” His repairs included replacing a cylinder and its piston with original Thor parts, replacing one of the pedal spindles, and numerous other bits and pieces. The Thor’s rear wheel was toast; Mulholland fitted a non-original rear wheel but later found a Thor original with matching blue paint and pinstripes. Mulholland rebuilt the Bosch magneto to factory specifications and he did the same with the Thor carburetor using original Thor parts. Incredibly, when he bought the Thor from Paxson’s family, it still had its original Firestone “No Skid” tires (Mulholland removed those and replaced them with Coker reproductions). Other wear items and soft parts were replaced. Other than these changes, the 1913 Thor you see here is unrestored. The paint is original, as is the optional rear-mounted aluminum two-speed transmission (a $40 option in 1913). In Mulholland’s later years, a hip injury kept him from working on, starting, or riding his Thor, but the Thor remained his prize possession. Mulholland passed away in September 2018 and ownership of the Thor passed to his family.

The Aurora Automatic Machinery Company

The Aurora Automatic Machine Company played a key role in early American motorcycle development starting with Indian, extending to other manufacturers, and culminating in the production of Thor motorcycles. Aurora, founded in 1886, initially produced forgings, coaster brakes, and other parts for an emerging American bicycle industry. In 1899 Aurora’s Oscar Hedstrom built a gasoline engine that was noticed by bicycle racer George Hendee. Hedstrom and Hendee’s interests and personalities clicked, and in 1901 they formed the Indian Moto Cycle Company in Springfield, Massachusetts.

Indian initially subcontracted their castings, forgings, machined parts, and engine production to Aurora. In 1902 Indian built 137 motorcycles; Aurora manufactured all Indian engines that year and continued to do so until 1906. The contract between Aurora and Indian allowed Aurora to sell engines to other motorcycle manufacturers (with royalties to be paid to Indian). It prohibited Aurora from selling complete motorcycles but allowed Aurora to sell kits using Aurora engines. As a result, at least six other motorcycle manufacturers (including Sears) used the Aurora engine and other Aurora components, with all looking very much alike (the cover of Thor’s 1913 Directions – How To Operate Thor Motorcycles notes “There are now 65560 Motors in use”).

The emerging motorcycle market was big and promised to get bigger, and the vertical integration draw was more than Aurora or Indian could resist. In 1903 Aurora formed the Thor Moto Cycle and Bicycle Company. Indian took casting and machining operations in-house, and by 1906 Indian was building its own engines. With the loss of Indian as a customer, Aurora started selling complete Thor motorcycles, and by 1908 they had opened their own dealerships. The first Thor was a single (Charlie Chaplin owned one), followed in 1910 by an odd-looking 1,000cc V-twin (the rear cylinder stood straight up and the front cylinder inclined forward). Thor added a redesigned clutch in 1911 and they changed the V-twin design in 1912 to incorporate push rods and thinner rockers. That same year, Thor oriented the cylinders symmetrically along a vertical axis (similar to today’s American V-twins, and as you see in the photos accompanying this story). In 1913, Thor offered the 625cc Model W single and the 1,000cc Model U twin. 1914 arrived with an optional 76-cubic-inch V-twin that could be ordered with a Schebler carburetor and the addition of floorboards (prior to that year the bicycle pedals served at footrests). Along the way, Thor motorcycles incorporated automatic intake valves, optional battery or magneto ignitions, lights, and different colors. The 1913 Model U 1,000cc twin was available in either blue or white.

The world was changing in the early 1900s and the changes did not bode well for Thor. Thor moved manufacturing from Aurora to Chicago and in the process lost many of their dealers. Thor added a more complex hub transmission in 1914; the added weight induced rear wheel spoke failures. Thor developed a three-speed transmission with reverse for sidecar applications hoping to secure a military contract but failed to win that business. Finally, World War I took too many potential customers to battlefields in Europe. By 1916, Thor Moto was no more.

Thor’s manual for the 1913 Model U makes for good reading. With no shortage of hyperbole, Thor described the Model U as the “most powerful Motor-cycle yet known, with unlimited speed. It will be the boss of the road and the pride of the boulevard.” It continues with “Several of the most noted gasoline experts in the United States have pronounced this new 7 H.P. Twin Cylinder Motor, positively the most mechanically perfect internal Combustion engine of the age.” As a guy who has written ad copy, I knew this was good stuff. Who wouldn’t want to be the boss of the road and the pride of the boulevard, riding the most mechanically perfect internal combustion engine of the age? Beyond the salesmanship and hyperbole, Thor’s manual included detailed instructions for assembling the motorcycle, adjusting the valves and several other maintenance actions, and how to start and operate the motorcycle. I thought the maintenance descriptions were great; very few motorcycle manuals today include this information.

Starting and Riding a Thor Motorcycle

To start a modern motorcycle, we turn on the ignition, touch the starter button, and go. Turn back the clock 15 years or so and we had to open fuel petcocks, close chokes, turn on ignition switches, and hit starter buttons. Back up 60 or 70 years and, for the most part, we would have to add kickstarting to the mix. Go back a century or more (and for this 1913 Thor, it would be a cool 110 years), and starting a motorcycle was a far more complex activity.

A Thor motorcycle had to be on its stand to get the rear wheel off the ground (why will become clear shortly). A rider had to put the bike in gear by pushing the clutch lever forward (the large lever along the engine and fuel tank). If equipped with the optional 2-speed transmission, the bike had to be in second gear (accomplished by turning the T-handle on top of the clutch lever to align it with the direction of travel). The ignition had to be retarded with the right twistgrip and the throttle opened slightly with the left twistgrip (both stayed where set; there were no return springs). The compression release, mounted forward of the right twistgrip, had to be locked open. The engine had to be primed, the choke closed, and petcocks opened to allow fuel and oil flow. Priming involved taking a small amount of gasoline (from either the tank’s forward fuel access port or the fuel filler cap extractor) and pouring it directly into two intake domes (one on each cylinder; the intake domes have threaded ports for this purpose). Closing the choke involved rotating an air adjustment stem above the big tomato can carburetor’s float chamber and turning a throttle valve adjustment thumbscrew behind the carburetor. Having accomplished all that, a Thor rider would now be ready to crank the engine. The Thor has two chains (one on each side of the motorcycle) and a set of bicycle pedals that did double duty as footrests. The rider would mount up and pedal like Lance Armstrong charging the Col du Tourmale. Pedaling spins the rear wheel, which then transmits rotational inertia through the rear-hub-mounted transmission, which drives the chain on the Thor’s left side, which spins the 61-cubic-inch V-twin.

Once the process outlined above attained sufficient rotational inertia, the rider could release the compression release. If Thor and the other Norse gods were smiling (Thor was the Germanic god of thunder and lightning, which somehow seems appropriate), the engine would awaken and the opening chords of a delightful V-twin symphony would follow. Then, the rider had to pull the clutch lever back to disengage it and reverse pedal to stop the rear wheel (there’s a coaster brake back there, the only brake on this motorcycle). While the engine warmed, the rider would advance the ignition with the right twistgrip, open the choke (again, requiring two separate actions as explained earlier), and then (as Thor wrote with Aurora engineering precision) apply “a trifle” of throttle with the left twistgrip. If it was a cold day, Thor recommended holding a rag soaked in warm water around the carburetor’s float chamber.

The Thor’s copper fuel and oil tank has four fittings on the top left rear just forward of the seat, and three fittings below the fuel tank (also on the left side). The fuel filler cap is the first of the fittings on top. The Franklin Automobile Museum’s Thor has the optional fuel extraction device to withdraw gasoline for priming. The second filler cap is for oil, with a short oil vent tube behind it. The last fitting on top is an oil flow needle valve, which could be used to regulate the amount of oil routed to the Thor’s total loss lubrication system. Thor recommended any “standard grade gasoline,” but advised straining it through a chamois. They made the same recommendation for oil, noting, “Oil is more necessary than gasoline, as suitable oil cannot be obtained along the road as easily as gasoline.” Two fittings and a sight glass are underneath the tank. The first is a fuel access port where the rider could draw fuel, as Thor noted, “for any purpose.” The second is a petcock that allows fuel flow to the carburetor. The oil sight glass shows the presence of oil, and a few inches below it, an oil line petcock on the oil line allows oil to flow to the engine. Presumably, failure to open this valve would void any warranty that might have existed, but not to worry. Thor’s manual stated “The Chief of the Service Department is a man of Skill and Discrimination. The service Department makes PROMPTNESS its aim. It is the plan of the Service Department to render PROMPT SERVICE rather than to ask questions.”

The Thor’s total loss lubrication system would consume a quart of oil every 50 to 300 miles depending on conditions and riding style. The oil tank holds one gallon. With a top speed somewhere between 50 and 65mph (depending on conditions and if the motorcycle was equipped with the optional two-speed gearbox), a Thor wasn’t likely to run out of oil. “They smoke a lot,” Paul Jacobson told me, “so as long as you see blue smoke, you’re good.” Paul is a man who would know; he rode his 1914 Thor V-twin 2,000 miles in the 2018 Cannonball Run.

As the throttle had no return spring, it could maintain a high idle (or any other setting, for that matter). With the Thor engine percolating satisfactorily, the rider would roll the motorcycle off the stand, put it in first gear by twisting the T-handle atop the clutch lever (such that it was perpendicular to the motorcycle), and feather the clutch lever forward to start moving. Once underway, both the throttle and the timing could be adjusted to suit riding conditions. Shifting was accomplished in accordance with Thor directions (“in shifting gears it is advisable to have motor speed as low as possible”). One can imagine that operating the throttle, the clutch, and the shifter (all with the left hand) kept a rider busy.

Vintage Thor riders have described the ride as spirited, with “adventurous” braking. A Thor motorcycle averages around 30 miles per gallon. If that seems like poor fuel economy compared to today’s motorcycles, recognize that gasoline was about 15 cents per gallon in 1913.

An Arizona Sunset Ride

The 1913 Thor gracing these pages was last ridden in 2019 in Tucson’s Richland Heights neighborhood near the Franklin Automobile Museum. The Museum had a special event, and the Thor you see here was joined by previously-mentioned Paul Jacobson and his 1913 Thor. On that 2019 Tucson ride, the Thor’s fuel petcock mount failed, and it has not been repaired yet due to concerns about damaging the copper fuel tank’s original paint, but the current owners tell me it will be repaired and the bike will run again. MC

Originally published as “Early American Twin” in the May/June 2023 issue of Motorcycle Classics magazine.