8. KR750

Harley-Davidson KR750 Ad

If the K model was the predecessor to the Sportster, the KR750 was the granddaddy of flat-track racing. It was the popular choice from the early Fifties until the late Sixties, as racers famous and obscure rode the side valve ‘Class C’ stalwart to countless trophies the world over and was so dominant that in 1969 the AMA rules were tweaked to allow British and Japanese bikes to actually compete.

Paul d'Orleans The Vintagent

Paul D’orleans, aka The Vintagent

“Everyone knows I’m not a huge fan of ‘the bar and shield,’” The Vintagent, Paul d’Orleans, told Motorcycle.com. “But I do have a favorite. For me, the most exceptional H-D ever built was the late 60s KR TT racer. Its development was taken further than any other racing engine, ever. How they managed to squeeze 150 mph from a 750cc side-valve engine is still a miracle of intense and inspired tuning.”

Veteran moto-journalist Mark Gardiner, author of “On Motorcycles: The Best of Backmarker,” agrees. “I know I’m not the only one who’ll choose the KR750. Although the motor was primitive, tuners like C.R. Axtell devised many ‘hot rod’ tricks to keep it competitive with the British bikes that were allowed in the class,” Gardiner says. “I read one guy mixed oil with jeweler’s rouge and put that in the transmission. Then he spun the tranny for hours with an electric motor, letting the gears lap against each other. Finally, he drained the polishing mix, thoroughly cleaned it, and replaced all the bearings. The result was a tranny with the absolute minimum friction.”