Restorations, Survivors, and Originals

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The success of the OHV 1936 61ci EL Knucklehead prodded Harley into development of OHV versions of their larger (74ci) and smaller (45ci) engines. The OHV 74ci FL debuted in 1941, but the OHV 45ci did not appear until 1957, as the Sportster.


The biggest improvement of the 1936 EL was not overhead valves - it was the recirculating oiling system. One year later, in 1937, the total-loss VL was replaced by the recirculating UL, and the total-loss 45ci RL was replaced by the recirculating WL. Conversion of the 74ci and 45ci to OHV was begun. This was a much simpler task, as it only required fitting OHV top ends to the new bottom ends.

In February 1939, two factory test riders set out from Milwaukee - Art Kauper on a prototype OHV 74ci, and Art Earlenbaugh on a prototype OHV 45ci. They fought their way out of the Milwaukee snow, down to sunny Florida and through miles and miles of Texas, before heading back to the factory. The trip lasted six weeks and 5,000 miles. Both machines ran well, and the only problem (besides snow) was a flat tire on the 74ci. Earlenbaugh had glowing priase for the 45ci.

The factory tore down the bikes for evaluation. The 74ci was approved for production for the 1941 model year. The transmission on the 45ci was determined to be not strong enough to handle the additional power of the OHV. Management felt the cost of an improved transmission could not be recouped in the selling price.

Then WWII put OHV 45ci development on hold while the factory cranked out zillions of flathead WLAs.


After WW2, Harley-Davidson took a new direction in OHV 45ci development - unit construction engine/transmission. Harley engineer John R. Bond proposed a very radical design - all-aluminum, 60-degree (not 45°) cylinders, single camshaft placed high between the cylinders, short pushrods, chain drive for both camshaft and generator, valves with torsion bars instead of coil springs, and each cylinder had its own Linkert carb.

The prototype engine was available around 1948, and it was first installed in a modified WL test chassis. Later, an entirely new chassis with swingarm rear suspension was developed, as shown in the photo. Testing uncovered problems with the new engine. Inadequate cooling caused overheating in the high camshaft area, there were piston problems, and the valve torsion bars tended to break.


While the KL problems were slowly being worked out, sales of the flathead WL were steadily declining, and the British Invasion had begun. Harley needed something to compete in the middleweight market, and a second concept was developed. This would build upon the strong points of the KL, like unit construction and swingarm frame, but without the problems of the KL's top-end design. The result was a melding of the KL's unit construction bottom-end with the WL's proven flathead top-end.

This newspaper article shows Mr. Oberhofer astride not a Sportster, but a prototype Model K. The front-end and gas tank are unmistakably “K”, but the rest of the bike appears to be “bits and pieces”. We'll leave discussion of those bits to our Forums, but the rear fender probably came from the 1951 Harley Hummer.

Harley decided to bring the K into production, and let the KL languish on the back burner. The K was not without its own development problems. Harley wisely continued to offer the venerable WL during 1952. Although announced in Fall 1951, quantity shipments of the new Model K did not occur until midway through the 1952 model year. The Model K temporarily filled the void in Harley's lineup, but an OHV 45ci would remain a dream for a few more years.

1957 XL


Most of the OHV WL info and the photo comes from Herbert Wagner's excellent book “Harley-Davidson 1930-1941, Revolutionary Motorcycles & Those Who Rode Them”. Available from Schiffer Books. You should get one!

Mostly Ironheads provided the KL information. KL Photos are from Mostly Ironheads website and The French Owl's defunct KRXLRTT website.