If you're into flat track racing, and on the half-mile or mile tracks, you know that the Harley-Davidson XR750's since the early 1970's have been a favorite weapon of the factory team and privateers. They stopped production of the XR750 in 2015, so that's better than a 40 year production run and use in competition. They are still used today though the Indian factory team and privateers who use the FTR 750 Indian have been the national title holders recently, since 2017. The KR flathead H-D racer was the predecessor to the XR750 OHV engine. The Sportster cases and layout was the basis for the XR750, and there was an aluminum/cast-iron hybrid design before the all-aluminum XR750 was released. That's what this is. Dick O'Brien, H-D racing team leader was familiar with Jerry Branch, and had used his input on cyl head flow for the H-D racing efforts. Between H-D factory engineer Bill Werner and Branch's contributions, the XR750 became one of the most successful dirt racers of all-time.
The KR flathead and the XR OHV were also used in roadracing, and as late as 1968, a H-D KRTT flathead was ridden to victory at the Daytona 200 by Cal Rayborn. An interesting experiment in aerodynamics by Harley-Davidson before that race resulted in a KRTT flathead engine in a much-smaller motorcycle, which proved the value of aerodynamics by being faster around the track than the full-sized H-D KRTT. However, Cal Rayborn was 5' 10" and the smaller bike wouldn't allow him to be able to endure the distance of 200 miles at Daytona. He chose the larger motorcycle, and still won. Jerry Branch And The Harley-Davidson Midget
The difference in size is apparent:
Testing by H-D at Willow Springs CA prior to the 1968 Daytona 200, with the standard-size H-D KRTT and "the Midget," with its Caltech-designed (California Institute of Technology, one of the best technical schools in the country) aerodynamic improvements:
"The Midget" benefitted from some innovative layout and design. The dry-sump oil tank was aside the left flank of the engine. The welds weren't pretty-but the design allowed a six mile an hour increase in top speed.
Back to the bike pictured above in the painting:
A guy in Great Britain saw a Harley-Davidson streetbike at a show. He liked it so-much, he bought it. Trying to find information, he contacted Allen Girdler, a motojournalist and racer, and asked him about the bike, if he "knew anything?"
Girdler, seeing the serial number of the engine, asked the owner, "you don't know what you've got, do you?" That was a big clue: 69XR001.
Read the article to learn the history of one of the most successful dirt track racing engines of all-time, and a factory prototype "after hours" project. The 1969 Harley-Davidson XR750 Werner "Prototype" Flat Track Racer
