Blown Away by a Blown 1940 HD ULH
'Down Under' Flathead would have been a complete terror back in its day.
Ground Up
Boosted by a supercharger, this 1940 ULH from 'Down Under' might just blow you away. Nicknamed 'Cojones,' the side-valve Bobber was built from the ground up by Evolution Custom in Mona Vale, Australia. Compared to today's big horsepower builds, the blown Flathead's output is modest to say the least, but would have been a complete terror back in its time.
Blower Off
Like most custom projects, the ULH has a circuitous backstory. Owner Paul McKinnon explained how a conversation with his friend Bill got the build rolling. “A while back we put the blower set up on his 1939 side-valve. I made the pipes and manifolds, but then he [Bill] wanted to ride it around Australia, so he took the blower off, and it was never to go back on.”
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Project Engine
Bill, who also happens to be a collector of pre-war Harley-Davidsons, did not want the blower project to be abandoned. McKinnon explained that his obliging friend provided him with a 1940 ULH project engine. “Bill scrounged around and found most of the bits I would need to get an engine bolted together.” All McKinnon needed now was to find or better yet, scratch-build the rest of the bike.
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Shared Bore
Introduced in 1930, Harley-Davidson's Flathead was produced for over forty years in various incarnations. The 80 cubic-inch ULH was a high-compression variant produced from 1937 to 1941. Beginning in 1940, the larger UH engine received forged aluminum cylinder heads with deeper fins for improved cooling. For cost-effective production, the UH engine shared the same bore and pistons and as the Knucklehead.
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Sorted Engine
McKinnon elaborated on his parts engine and the Aisin AMR300 from a Subaru. “The motor is made up of some new old stock and some second hand. It runs like a Swiss watch for its vintage...I’d estimate about 35 to 40 horsepower with the 6psi of blower pressure it’s running.” With the engine sorted, McKinnon turned his attention to the frame and frontend — or lack thereof.
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Forty Hours
The frontend brings together old and new technology. To fabricate it, McKinnon sought help from another friend. He explained, “A mate of mine has a CNC mill and we sat together for around forty hours and came up the programs to cut it. Once I had a complete frontend, I bolted it to the frame and set the whole lot up in a jig.”
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Reworked Aluminum
Fabrication work did not stop with the frontend, almost all the other components were handmade. McKinnon elaborated on the process. “I made every bracket, the jockey shifter, clutch and brake pedal, aluminum oil tank, blower piping, exhaust, and the bars.” The gas tank was an eBay find that was modified to suit the Bobber style and a reworked aluminum filler cap with an internal breather.
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No Way
The ULH's exhaust was bent out of stainless steel tubing, and the Cocktail Shaker exhaust is from Trojan Classic Motorcycles. The small radius rear fender was custom made by 7 Metal West in Milwaukee, Wisconsin, and wraps around a Shinko MT90 tire. When asked if he was going to sell his 'Cojones,' McKinnon replied, “No way. This one’s mine.”
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