Knucklehead Greatness!
70th Anniversary of Harley-Davidson's
Immortal 61 OHV
By Herbert Wagner

Part I
"I imagine personal sentiment enters into that, but the first 61 Overhead was my favorite" -- William H. Davidson

Around this date in 1936 a new motorcycle was sparking comments like these: "My idea of a super bike." "What every rider sees in his dreams." "What I call class." "Has got the boys on fire."

The motorcycle was Harley-Davidson's new "61 OHV" twin, commonly known today as the Knucklehead. While retaining traditional features the 1936 "EL" model sported innovations such as overhead-valves, a circulating oil system, full roller-bearing motor, double-cradle frame, chrome-molybdenum tubular forks, built-in instrument panel, and welded-steel teardrop tanks. Coupled to an almost indestructible four-speed gearbox the new overhead-valve twin gave stellar high-speed performance and reliability plus futuristic good looks.

There was also mystery surrounding the 61 OHV. For years rumors had been afloat of something radically different on Bill Harley's drawing board. But when the new "Sixty-One" finally arrived it surfaced out of nowhere without Milwaukee's usual trumpeting fanfare. People were electrified and amazed. First glimpsed by dealers in late 1935, Tom Vandegrift of Albert Lea, Minnesota, recalled: “It was announced we would have a sensation... Then they pulled the cover off. We always expected to see something new, but that Sixty-One was radically different because it was an overhead twin."

Before long the term "61 Overhead" would become a mantra for a motorcycle that embodied all the performance, reliability, and styling a rider could ask for. Few motorcycles in history have created such enthusiasm or have left such a legacy. From its first appearance the 61 OHV possessed a mystical glamour and allure it still holds today. With the Knucklehead old Bill Harley had reinvented the American motorcycle once again.

But it wasn't luck or just one man behind the 61 OHV. Nor did it burst into full creation overnight. The EL's origin is a complex blend of forgotten ancestors and changing strategies developed over the years. From concept to showroom marvel the Knucklehead was born of experience, hard work, and desperation. There was no laziness involved this time. New life had to be injected into the American motorcycle scene if Harley-Davidson was to survive at all.

Flash back to Milwaukee, Wisconsin, in the early 1930s. Motorcycle sales had nose-dived and the directors of Harley-Davidson felt like men walking the plank. For years William S. Harley and brothers, Arthur, Walter, and William A. Davidson had seen a downward spiral in motorcycling as automobiles increasingly dominated American roads. They recalled the old adage: "Everybody needs a can of tomatoes, but nobody needs a motorcycle."

American motorcycle production had peaked in 1913. After World War One nation-wide motorcycle registrations began dropping too. Sport ridership grew so weak that in 1927 Walter Davidson predicted: "the pleasure sport riding motorcycle is largely a thing of the past in this country and not to be depended upon for future business." Then came the hammer-blow of the Great Depression when Super-X (Excelsior/Schwinn) halted motorcycle production. After that Indian and Harley limped along on commercial and police sales, wondering if they could stay in business at all.

Curiously, not long after predicting the end of the sporting market, Walter Davidson abruptly reversed course and announced: "In the pleasure field there seems to be a very great market [that] can be greatly stimulated by... bringing out new and better models."

Since the soul of a motorcycle is little more than a gasoline engine cleverly shoehorned into a bicycle style frame, the sporting side of the business had always revolved around the mill, engine, motor -- call it what you will. If Harley-Davidson wanted to stimulate sales to sport customers, a new emotion-packed motor was needed, but which motor?

Hunting for a new engine Harley-Davidson first considered that old American mainstay: the four-cylinder. Smooth-running and sophisticated "fours" had always represented the Ultima de Luxe of the pleasure sport market and Pierce, Henderson, Ace, Cleveland, and Indian had all built fours.

In 1928 Harley-Davidson hired E.M. DeLong, experimental engineer from the Cleveland Motorcycle Co. to work on two completely new models planned for 1930: an 80-inch "4-cylinder" chain-drive machine and a 90-inch "4-cylinder" SHAFT-drive model.

Although details are lacking on these machines (author Jerry Hatfield has argued they were in-line V-fours), Harley obviously desired to appease that vocal element who hollered for "80-inch motors" by giving them all they wanted and more.


Evert DeLong is in the Flxi sidecar while Red Wolverton is on the Ace Four. The event was a speed trial for Ace, circa 1923. From the David Lemon collection.

Abruptly in early 1929 Harley's directors torpedoed the four-cylinder project after losing the Eclipse clutch patent infringement lawsuit with its cash pay out of $1.1 million. After some talk of putting DeLong to work improving the Cleveland Four and using that, the notion of a Harley four-cylinder was deep-sixed and DeLong was cut loose.

This luckless episode demonstrates that years before the 61 OHV was on the drawing board Harley-Davidson was looking for an exciting new motorcycle of outstanding technology to thrill the masses and to revitalize the sport.

Around the same time the Harley four project was dying in the background, Milwaukee was replacing the old "pocket-valve" motor (inlet-over-exhaust or F-head) of 1905-1929 with a new line of side-valve (flathead) engines. In the 1920s Indian had set the pace with its side-valve V-twin Scout and Chief models. At that time the side-valve had lots going for it: simple, clean, quiet, and easy to produce. By 1930, however, when the new 74-inch Harley VL came out, the side-valve was so identified with Indian that Milwaukee seemed to be copying the rival firm's motor!


(Herb) Circa 1931 mockup of aborted side-valve Model W sports double-cradle frame, tubular forks, instrument panel, and teardrop tanks that would later show up on the 61 OHV Knucklehead. Photo courtesy John E. Harley family.

While in some respects the VL was a good machine, it did not always meet rider expectations. Even beyond teething problems there were serious flaws in its "fighting heart." By the early thirties there were good highways and guys who wanted to travel fast. Not just quick bursts, but hours of high speed running. In spite of its powerful-as-a-locomotive look, hard use revealed the side-valve's dirty little secret. With all the twists and turns inside the cylinder it didn't breathe well at high rpm. The oddly-shaped combustion area had "dead corners" that wasted expanding gases, retained heat, and "coked up." Riders made things worse by overusing the handpump on the VL's total-loss oiling system.


While in many respects a good motorcycle, weakness in the side-valve VL engine showed up during prolonged high-speed operation.

So long as riders didn't push the side-valve too hard, things were okay. But prolonged running at high speed -- especially with bad plugs or a lean carburetor -- and the demon of overheating would rear its ugly head. A windshield or sidecar compounded the problem. And because the hottest part of the side-valve engine (the exhaust valve) sat next to the cylinder bore, local hotspots and distortion could occur, thereby causing piston seizure or worse. This letter to your Uncle Frank tells the tale:


Melted Aluminum Pistons
"Uncle, my... Harley [VL] has turned out to be a smelting furnace. She blew up the other day and upon taking off the cylinder heads, I find that the front piston has a hole fused, melted, right through the top. Aluminum was splattered all about and it looks like somebody got in there with a welding torch."
Uncle Frank confessed to the pernicious wasted heat in the side-valve and advised: "Never open a throttle and hold it there but rather every few seconds [emphasis mine]...momentarily close the throttle to allow cooling gases to pass into the motor and lubrication work up from the cool base."

Overheating and piston failure would haunt the big flathead for the rest of its days. Not a situation agreeable with Harley's reputation for reliability or desire to invigorate the sporting market. What good was an engine that couldn't take it?
Harley's next strategy was to improve the VL in the never released 65-inch model "W" slated for 1932 in a double-downtube frame. They got as far as the mockup stage before W ran out of air in Harley's boardroom. By mid-1931 company directors were arguing whether the new model was worth the effort. That sent Bill Harley back to the drawing board for fresh ideas.

Here we arrive at a crossroads in Harley-Davidson history. As these events were taking place against the backdrop of the Great Depression, we might expect the penny-pinching founders to pursue an ultra conservative course. Why risk launching something new in an abysmal business environment?

But these guys had faith in the American system and that someday economic conditions would improve. What would Harley then offer young factory men who formed the bulk of the pleasure riding market? Out of a job now and unable to buy much of anything, this condition would change once they got back to work and their desire for new motorcycles was released. Would Harley greet them with the same ho-hum product or something striking deeper emotions like the sport had witnessed back in the teens?


Andrew Strand's overhead-valve/overhead-camshaft Cyclone motorcycle built at St. Paul, Minnesota, was the peak of advanced American technology during the teens.

Harley's founders must have looked back with fondness to the days before World War One when novelty and excitement were industry watchwords. When yearly national motorcycle shows demonstrated innovation and novelty.

Around 1910 some forward-thinking firms began offering high performance overhead-valve engines. In fact, Harley's own early employee and racer, Perry E. Mack, designed one of America's first full overhead-valve motorcycle engines (see: The Antique Motorcycle, Winter 2004). Between 1910 and 1914 Mack's single and V-twin OHVs powered Waverley, Kenzler-Waverley, P.E.M., Jefferson, and Breed motorcycles that proved speedy on road and racetrack. The similar Pope overhead (1913-18) dubbed itself "Champion of the Hills." Andrew Strand's fabulous Cyclone motorcycle built in St. Paul, Minnesota, appeared like a brilliant flash on the horizon with stunning overhead-camshaft technology. Seventy-five years later old timers from Harley-Davidson remembered the "Yellow Peril" at Dodge City in 1915 and how it had ruled the track before limping into port with mechanical trouble.

After World War One these advanced American overheads were all belly-up. The only OHV engines to be seen were special racing jobs built by the surviving Big Three and out of the ordinary rider's reach. The factories more or less promoted the belief that overhead-valve engines were prone to "cracking up" if a valve broke and that speed gains were not worth the risk. Yet these early overheads had drawn attention. Guys had even grafted Jefferson or Pope overhead parts to the bottoms of other brands for more speed and power!

Then, in the early 1920s, OHV fever exploded in Great Britain when postwar engineers began applying new technology to motorcycle engines and overhead-valve singles began carrying off high racing honors. A variety of wildly-popular 350 cc OHV singles appeared on the British market. With low operating and licensing costs these "giant killers" peaked near 70 mph, beating bikes twice their size. Developments surged ahead until a 1924 350 cc OHC Charter-Lea-Blackburne broke 100 mph at nearly 6000 rpm!

This was bewitching stuff and Harley-Davidson followed developments overseas by subscribing to English motorcycle journals. When these small overheads began cutting into Harley's foreign sales the Italian distributors made a trip to Milwaukee pleading for a small OHV to compete with English brands.


Primarily intended as an export model, the 21 OHV (350 cc) Single was no "baby cart" due to big bike features and peppy performance.

To meet this challenge Bill Harley and his engineering crew brewed up a pair of 21-inch (350 cc) single-cylinder models for 1926. The "Single" would be the smallest displacement Harley-Davidson to date; even smaller than the 440 cc Model One of 1905.

Offered in both side-valve (B) and overhead-valve pushrod (BA) versions, these appealing little bikes were built to the same high standards as Harley's bigger models. When Uncle Frank rode the new Single he remarked: “When my turn came to try out this new member of the family, I kinda felt like I had been asked to go strolling a baby cart. But, that little boat is no baby cart -- no siree.”

Dubbed the "80 mile per gallon" bike guaranteed in flathead form to rust the hinges off your wallet, the overhead-valve version (21 OHV) soon gained the moniker "Peashooter" for its speedy racetrack performance. There are still guys in Australia and New Zealand crazy for the 21 OHV; a testament to its popularity down under.

In the USA, however, Harley pushed the side-valve Single instead. Lost in another pipe-dream during one of Milwaukee's safe-and-sedate moods, Harley incorrectly thought that auto drivers could be tempted back to motorcycles on price alone. Yet everybody who rode the little 21 OHV to its peppy 65 mph/4600 rpm redline knew like Hap did that it was no baby cart.
The next development came outside of the Harley-Davidson factory. Just as guys in the teens had grafted Jefferson OHV parts to other bottoms, Harley "slant shooters" (hillclimbers) would soon do something similar out of desperation.

Caught napping in the new 45-inch (750 cc) hillclimb class in 1926, Harley had nothing competitive against the 45 IOE Super-X or Indian 45 OHV hillclimbers. Harley riders were forced to climb with the little 21 OHV and occasionally they even won.

But for real dig-out power V-twin inches were needed and in 1927 a few enterprising Harley dealers like Oscar Lenz and Ralph Moore constructed special "homebrew" engines using pre-1930 "Two-Cam" 61-inch bottoms topped with reworked 21 OHV Single heads and cylinders. These 45-inch OHV homebrews drew amazed comments like this one in MotorCycling: "No, we did not hit the bottle... Moore took a 61 [Two-Cam] Harley, junked most of the motor except the cases, and constructed a 42 [sic] cubic inch Harley, using the cylinders and pistons from two 21-cubic inch O. V. Single Harleys."

By this time Harley-Davidson was already working on the new four-cam 45 OHV (DAH) hillclimb engine that would appear in 1929. But for 1928, probably goaded by Milwaukee dealer Bill Knuth, Harley's experimental racing department took the homebrew concept one step further. Herb Reiber, one of Knuth's "Lone Star Riders" was also assistant instructor in Harley's factory service school and was a paid factory hillclimber. By trade Reiber was a pattern maker. Fancy that!

Evidence is sketchy, but documentation at the AMA museum tells that Reiber modified the 21 OHV cylinder pattern and that six pair of special cylinders were cast up. Then 21 OHV heads were reworked and with the newly cast cylinders installed on Two-Cam bottoms. The resulting hybrid was a Two-Cam/OHV. Combined, the 21 OHV bore and the 61-inch Two-Cam stroke resulted in an overhead-valve V-twin motor yielding 45.44 cubic inches (744.6 cc). Antique bike restorer and builder Mike Lange, who worked on one of two known surviving Two-Cam/OHV engines observed: "The intake manifold was done up very professionally with a nickel [welding] rod.... Along with the cylinders it’s my opinion that these were done at the factory."

These factory 45-inch Two-Cam/OHV hillclimbers were ridden on the slant in 1928 by Herb Reiber and Art Earlenbaugh. They were good enough for Earlenbaugh to win second place at the Muskegon sectional championship which allowed Bill Knuth to crow: "The motors in these hillclimbers are the most highly-developed internal combustion engines in the world!"

Harley's own Enthusiast let slip this clue after the New Munster climb in August: "All kinds of shooting irons were on the slant. Some ‘Home-Brew’ 45s and some that weren’t home brew... Art Earlenbaugh, the Milwaukee sheik, took his ‘cellar made’ 45 Harley-Davidson over the wall in the 45 event. Which, of course, was considerable show for Art and his ‘laboratory model.’"

Cellar made? Laboratory model? An interesting choice of words when you consider that Harley's experimental department was located in the basement. Almost certainly these guys were riding stealth factory mounts.

So stealthy in fact that this uncatalogued hillclimber escaped the radar screen of collectors and historians for decades. When one finally popped up at Davenport a few years ago, people wouldn't believe it was real. But let Floyd Smith tell that story, the guy who found and recovered Reiber's own 1928 Two Cam/OHV laboratory model: "They stood around saying how phony the engine was. A homemade job. That kind of scenario. Then my buddy, Chuck Wesholski, spoke up. He said, ‘You guys laugh if you want, but you’re looking at an engine that none of us knew Harley ever built. It’s not homemade, it’s factory. You damned fools are looking at the missing link!’"

For years people have wondered where the Knucklehead came from but nobody had a good answer. Faithless types speculated it was copied from an English OHV; others said airplane engine. But when you set the old 1928 "laboratory" hillclimber with its distinctively shaped Two-Cam bottom, angled pushrods, and overhead-valves alongside a Knucklehead the words "missing link" suddenly make perfect sense.

Knuckleheads will continue in the Winter issue of The Antique Motorcycle.