Yes, Harley-Davidson has produced 4-cylinder motorcycles in its history. The most notable example is the Harley-Davidson VR1000, which was a sportbike designed for racing in the Superbike World Championship. The VR1000 was introduced in the late 1990s and featured a liquid-cooled 996cc V-twin engine with a 60-degree V-angle. It had a DOHC (Dual Overhead Cam) configuration with four valves per cylinder.
The VR1000 was a significant departure from Harley-Davidson's traditional air-cooled, V-twin cruiser motorcycles. It showcased the company's attempt to compete in the high-performance sportbike segment. However, despite significant investment and efforts, the VR1000 did not achieve notable success in racing and was eventually discontinued.
It's worth noting that while the VR1000 is the most prominent example of a 4-cylinder motorcycle produced by Harley-Davidson, the company's mainstay has been its air-cooled, V-twin engines, which have become synonymous with the Harley-Davidson brand.