HD Cutaway 3

This Harley-Davidson XR750 “cut-away” bike illustrates the most dominant production racer ever built. It has reigned over America’s dirt track ovals for an amazing 40 years.
HD Cutaway 1
Although it has been tweaked and refined, today’s XR750 racers are very similar to the first “alloy” versions from 1972. Sharing direct lineage with earlier Harley production racers, the WR and the venerable KR750 both side-valve engine designs, the first XR750 appeared in 1970; the infamous “iron” XR. The bike was a result of the AMA finally doing away with its 500cc OHV vs 750cc side valve engine rule. Starting in 1969 on dirt and 1970 on pavement, the new rules allowed a 750cc limit for all engine designs. Dick O’Brien and the Harley team began a crash course and came up with the new XR750, which in basic design was a destroked iron cylinder Sportster engine. The engine was housed in a proven KR-style swingarm chassis with Ceriani forks.The striking orange and black bodywork was the design of the Wixom Brothers. The engine made competitive horsepower, but the heat it produced led to self-destructive tendencies. Though the bike scored a respectable number of victories from 1970-’71, it also broke a lot. While stop-gap measures such as oil coolers and reduced compression helped, the factory knew what the trouble was and was concurrently building the improved “alloy” engine model. When it debuted in 1972, there were still teething problems to solve, but the basic package was a winner.
The factory produced small batches of the complete machine in 1972, 1975, 1978 and 1980. Since then, only the engine has been available, with the customer choosing an aftermarket frame from manufacturers such as Knight and C&J.The venerable XR750 has met and defeated many foes over its 40+ years in competition. It is today facing renewed challenges from talented teams fielding machines from Kawasaki, Ducati and Triumph. The reason for Harley-Davidson’s domination is often speculated. In short, it is a purely American design for the purely American sport of half-mile and mile dirt track racing. Its tractor-type power from the 45 degree twin is the perfect tool for that purpose. Times may have changed around the XR750, but it is still out there accomplishing its intended goal; AMA Pro dirt track domination.
HD Cutaway 2
Total Production – Approximately 530
Model – Harley-Davidson XR750
Year – 1972-1980
Engine – 45 Degree V-twin, Aluminum Barrels, OHV
Bore and Stroke – 3.125 X 2.98 Inches
Displacement – 45 Cubic Inches, 750cc
Brake Horsepower – 90
Transmission – 4 Speeds
Wheelbase – 56.75 Inches
Weight – 295 Pounds
Wheels – 19 Inches
Tires – 4.00 x 19
Brakes – Rear Disk
1 reply
  1. David Joseph Schroepfer
    David Joseph Schroepfer says:

    Building the engines took extensive mechancial skills and tools. Special bearings were used from Germany to get another race out of the engine. Normal stock engine from street bikes last many races.


Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *