The Harley-Davidson XR1000
(Page 2 of 5)
Choosing the pieces
Dick O’Brien, famed head of H-D’s racing department, took charge. A stock Sportster bottom end was specified, but using special barrels and heads. All this would be bolted into the new XLX chassis introduced for 1982, whose welded steel tubes gave it a more sophisticated look and feel than the old version, which had been made using individual castings. Harley’s engineers had figured out how to balance too stiff with too flexible, creating a frame that had the possibility of handling quite well, assuming the proper suspension components were used.
However, life wasn’t that simple, and problems with the XR’s development immediately began to show themselves. The XR750 alloy cylinders would not do, as they were too small (750cc) and even if enlarged they would not fit the XLX cases. New iron cylinders with an 81mm bore were made, and new aluminum pistons required new connecting rods. The V-twin’s fork-and-blade con-rods (one rod rides inside the other on the crankshaft), bolted onto the single-throw crankshaft, remained the same, as did the four rather low-lift “Q” camshafts under the right side cover, providing a broad and smooth torque curve.
One advantage here was that the new cylinders were designed to use through-bolts rather than the standard Sportster design, which had separate bolts holding the cylinders to the cases and then the heads to the cylinders. There was more finning to aid heat dissipation, but many owners still added an aftermarket oil cooler, including the owner of our feature bike. It’s a very sensible addition.
Complicating things further, the XR750 heads had to be recast for the XR1000. The new heads used slightly larger valves to allow for the increased 998cc displacement, and also offered better support for the valve guides, considering that this was intended to be a high-mile street bike, not a constantly rebuilt race bike. After basic machining in Milwaukee, the heads were all sent to flow-guru Jerry Branch’s shop in California. Branch did the porting and polishing, shimmed the double valve springs, and put in titanium collars and keepers. None of this was cheap.
One big difference between the iron XL and alloy XR heads was that the valves were set at an included angle of 90 degrees on the stock Sportster versus 68 degrees on the XR. This allowed for a shallower combustion chamber and a flattish-topped piston on the XR, which helped create a shorter route from the spark plug to the combustibles.
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