Offered by Bonhams this month .....

Factory outlaw racebike, less than 500 built
1964 Harley-Davidson XLR-TT
The XLR-TT came on the scene in 1958 and stayed in production until 1969, and is one of the rarer members of the extended Harley-Davidson Sportster family. 
Depending on which historian you subscribe to, there were between 200 and 500 XLRs made. Despite looking like a stripped XL Sportster, these were pure racebikes with no provision for lighting or other street amenities.

The XLR's performance came from its engine spec. While run-of-the-mill Sportsters went out into the world with their cams running in needle bearings and bushes, XLRs benefitted from friction-reducing ball bearings. Likewise, their crankshafts ran in roller bearings. The bikes had specific flywheels, pistons and connecting rods. Different cylinder-head castings allowed larger valves and a bumped-up compression ratio. Hotter cams were installed as well as a lightened valvetrain. Ignition was via magneto, moved from the right side of the engine to a tucked-up position ahead of the front cylinder. Even the XLR frames were special, built with a better grade of steel so the walls could be thinner and the whole assembly lighter.

This particular XLR-TT is one of 30 built in 1964. It is equipped with most of its original equipment, including some special factory parts like an aluminum rear fender and brackets, a Daytona-spec 8½-inch alloy front brake and Heco shocks.

Estimate: $45,000 - 65,000