Flat Track Legend
The sport of flat track racing is as American as apple pie, as are the machines built to race them. From its earliest days flat tracking was exciting and dangerous, as depicted in the cult classic film On Any Sunday.
Prior to 1970, Harley-Davidson used its old side-valve KR750 racer to win consistently in flat track and road racing. But due to an unexpected rule change the previous year, its bikes were suddenly outdated and too slow against its rivals, which were all now 750cc triples or twins with overhead valves.
In order to stay in racing – which the factory race department very much wanted – H-D had to come up with a new overhead-valve engine of 750cc. But times were tough at Harley then. It had a new owner (AMF) that was just finding its way while dealing with ongoing union troubles and strikes.
The only affordable option at the time was to convert the existing 900cc XLR into a new 750cc racer. This was done by shortening the crankshaft stroke, which proved to be more difficult than expected due to a number of issues, thus the need to modify other items including the cylinders and pushrods, to name a few.
A new frame was mated with Ceriani forks, Girling shocks and Borrani rims fitted to alloy racing hubs, which were the best available at that time. The fibreglass tank and seat were also new.
It was called the XR as it combined parts of the KR and XLR. Just 200 examples of these were produced to comply with race homologation rules.
Unfortunately, and largely due to the haste that this machine was put together, it was not as successful as Harley had hoped. The engine proved too fragile at times and it ran too hot due to cast-iron heads and cylinders.
Most of the problems were rectified over the course of the next year and by late 1971 the XR750’s engine was producing 80hp. The company had now gained valuable knowledge about what was required for the next model: the alloy engine XR750. These continue to be raced today and only this year – after a 45-year production run – has the company finally called it quits. It’s fair to say that without the iron XR the all-conquering alloy XR would not have been developed.
With the arrival of the new model, all unsold iron XRs were scrapped for ‘accounting reasons’, totalling more than 100 examples including race bikes. The worldwide registry for the 1970 XR750 currently lists about 60 surviving examples.
The XR story is incomplete without mentioning another American icon, Evel Knievel, who attempted now legendary stunts aboard his iron and alloy XRs with mixed results, given the lack of sophistication in motorcycle suspension at that time.
This article by Greg Cahir appears in Cafe Racer #2