Early OHV Harley was a One-Off Experiment

Better Described

Followers of vintage bike sales will recognize this one-off bike from its multiple auction listings and various descriptors. Sometimes called a prototype or 'mini' Knucklehead, the machine pictured here has more to do with Flatheads than a Knuckle. It is probably best described as an experimental 1938 Harley-Davidson, with a 45 cubic-inch OHV engine.

Various Designations

Only five such machines were reportedly made. This particular bike is apparently the rarest of the bunch because of its all-aluminum top end. It recently resurfaced in January 2022, at Mecum Auctions–Las Vegas, but has popped up with frequency in various listings since at least 2016. It has also been referred to as XE-4, a designation derived from its motor number.

Documented Running

The bike's unique motor is credited to William S. Harley, who was looking for a way to build on the existing 45 cubic-inch Flathead motor, while solving its chronic overheating problem. Board meeting minutes from Harley-Davidson's archives document the development and authenticity of this machine. It is considered to be the only complete and running experimental Harley-Davidson motorcycle in existence.

Authors List

The rare bike is featured in Harley-Davidson Motorcycles, 1930-1941 by Herbert Wagner, and Inside Harley-Davidson by Jerry Hatfield. Familiar with Motor Company historical matters, these authors describe the experimental machine as a 'second-generation' in the attempts to put an overhead-valve top end on a Flathead bottom. They also list the engine's displacement at 52 cubic inches.

Vintage Specialist

Wagner and Hatfield also suggest that this may be the only experimental Harley-Davidson to be released from the factory, although 'released' might be a stretch. The understood version is that Roy Egeberg, a former Harley-Davidson dealer in St. Paul, Minnesota, bought the mostly complete machine directly from William Harley. Egeberg then sold the bike to vintage motorcycle specialist and restorer, Daniel Pugens, in 1974.

Stamped Parts

Among the many write-ups about the experimental bike, one particular archived sale listing stands out. Although unverifiable, it is purportedly from Egeberg's widow. She writes that the motor had been blown up by Harley-Davidson in testing, but the broken bits had been welded back together. Verifiable is that the individual motor parts are stamped with 'EX' followed by various numbers.

Different Modification

Other known facts are that the 1938 bottom end is specific to the overhead valve top end. The motor is fitted with narrower cams and the cam cover itself is oversized. Modification to the lifter blocks allows for better oil scavenging. Among the many, slightly different parts, of the experimental machine are custom-made narrow stepped hubs with small spoke rims.

Little Replacement

While a small displacement OHV bike was an attractive proposition, Harley-Davidson ultimately decided it would be too costly to develop a new model. Shades of the design appeared as aluminum cylinder heads for the ULH, while the simple '45' Flathead rode into fame as the WLA. What could have been a 'little brother' to the EL and W-series replacement was shelved for good.

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