1972 Harley-Davidson XR 750
One of only 100 1972 XR 750 flat trackers built, and one of 200 in total
Serial Number 50
Harley-Davidson began production of its legendary XR750 V-twin flat tracker in 1970 as a reaction to changes in AMA rules. In 1934, to make motorcycle racing more accessible, the AMA set up new Class C regulations. This allowed production-based American 750cc side-valve and 500cc predominately British overhead valve engines. These regulations lasted for more than three decades but changed in 1969. New rules now allowed for any production 750cc engine to race in AMA events, effectively rendering Harley’s side-valve KR750 obsolete. Milwaukee’s response was the XR 750, ostensibly a de-stroked overhead valve Sportster XLR 45-degree twin-cylinder engine in a KR chassis. motor. For 1970 and 1971 the XR 750 racers utilised iron heads with lightweight aluminium alloy cylinders, but for 1972 the XR 750 received aluminium heads.
Following problems with overheating, legendary Harley tuner Dick O’Brien radically overhauled the short-stroke XLR 883 Sportster-based engine. The bore was increased to 79mm (from 76.2mm) and the stroke shortened further, to 76mm (from 80.8mm). The crankshafts and mainshafts were now one-piece forgings and the new aluminium cylinder heads included slightly smaller, 42 and 35mm, valves. These were set at much narrower included angle of 68 degrees, as opposed to the old head’s antique 90-degree angle. The new engine weighed 7.7kg less than the cast-iron version and featured 73 per cent more fin area. The compression ratio was 10:1 and with a pair of 36mm Mikuni carburettors on the right and twin reverse cone upswept pipes on the left, O’Brien and other tuners such as C.R. Axtell and Jerry Branch, eventually managed to extract around 90 horsepower. This engine was placed in the existing XR twin-loop steel tube frame with a lightweight fibreglass tank and seat, Ceriani forks, and twin Girling rear shocks. While Cal Rayborn did his best with the XRTT in US Grand National road races, the two-strokes soon consigned the XR 750 to dirt-track racing exclusively. Weighing only 145kg, the bike was well suited to young charger Mark Brelsford who returned the Grand National Championship to Milwaukee in 1972. The XR 750 then continued to dominate AMA dirt track racing for many years, winning the most races in AMA racing history and notching some 29 AMA Grand National Championships through to 2008. Harley-Davidson recognized that racers preferred to use their own frame and suspension for racing, and from the 1980 on, supplied only XR 750 engines. In addition to the dirt-track success the XR 750 was made famous by Evel Knievel who rode one in many of his stunt jumps and publicity events in the 1970s.
This 1972 Harley-Davidson XR750 flat tracker, serial number 50, was part of Jean and Francois Gagnon’s Musee l-Épopée de la Moto collection in Saint Jean-Port-Joli in Quebec, Canada. The museum opened in 2003 and two rare XR 750s were on display. When some of the collection was sold at by Mecum auctions in the US in 2020, this rare XR 750 was one of them. Every XR 750 was hand built in the Harley-Davidson competition shop, and this machine looks like it rolled out of the shop last week. This is an extremely significant motorcycle for Harley-Davidson and also for dirt-track racing.
To view high resolution images of the motorcycles, please follow the below Dropbox link;
https://www.dropbox.com/scl/fo/n5bcjb2nuoc16t4y3k5hs/h?dl=0&rlkey=exyqlbxilyvv4n3ue8jmppkbx
This motorcycle is sold unregistered.
