Harley-Davidson XR-750 Stop-Gap Racer

The iron-clad Harley-Davidson XR-750 was only a stop-gap model, but proved to be a great investment following the success of the alloy version.

The first XR-750 bowed in 1970. Initially the Ironhead engine used a single carburetor and straight pipe exhausts.

Flathead race engines finally became extinct November 1968, when the AMA Class C rules committee legalized overhead-valve 750cc engines for Nationals competition. Previously, overhead-valve engines were limited to 500cc displacement, while sidevalves could be 750cc. The new rules caught Harley-Davidson race team with its valves down, and Milwaukee’s juggernaut team entered the 1969 race season outgunned. Or so it seemed.

Despite running essentially obsolete equipment, H-D team rider Mert Lawwill answered the call with his trusty sidevalve KR-750 to win the coveted Number One plate. But 1969 was the KR’s swan song. Gene Romero, riding new Triumph OHV twins and triples, won The Plate for 1970.

Meanwhile Harley’s engineers readied their own overhead-valve engine for racing. Their immediate response was the XR-750, an engine with iron cylinders and heads — a distinctly different engine than the alloy-based XR-750 that was scheduled for 1972. The all-new alloy engine was intended for one purpose only — to crush the competition on the flat tracks of America, which it ultimately did, dominating dirt track ovals across America for the coming decades.

But the fascinating story is found in that first-generation XR-750 using an engine essentially jerry-rigged for racing based on Harley’s XLR, itself a 13-year-old design originally developed for customer 883cc Sportsters.

No surprise, Harley scrambled to make the XLR legal for Class C racing. New and lighter flywheels shortened the stroke from 82mm to 79.5mm, ratcheting down displacement to 750cc. A multitude of other modifications followed, including beefing up the right-side main bearing, replacing camshaft needle bearings with ball bearings, and so on.

4/16/2020 11:47:26 AM

I'm a BSA guy, but I did ride a Harley-Davidson - once. One of my shipmates in 1970 acquired a bright orange H-D XR-750. I was not "racing-savvy" at the time (still am not), but he let me ride it down the block. Besides having all the foot controls "wrong," it shook MUCH more than the A10 Road Rocket I owned. Yes, it had more power than was necessary for a one-block ride, but I was impressed by two things. First, no one could ignore that machine, either while being ridden or standing still. Second, I would not last 60 miles on a road trip without having to get off and "un-buzz" a while. Kudos to those who rode this model for long distances! A70 Rider

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