The Knucklehead Arrives: 1936 Harley-Davidson EL

The Harley-Davidson EL with its overhead valve engine took awhile to perfect but the wait was worth it.

1936 H-D EL

1936 Harley-Davidson EL

Photo by Sedrick Mitchell

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1936 Harley-Davidson EL
Top speed:
60.33ci (988.56cc) air-cooled OHV 45-degree V-twin, 3-5/16in x 3-1/2in bore and stroke, 7:1 compression ratio, 40hp @ 4,800rpm
Weight (wet):
515lb (234kg)
Fuel capacity/MPG:
3.75gal (14ltr)/35-50mpg
Price then/now:

The iconic “Knucklehead” — the overhead valve 61-cubic-inch V-twin introduced by Harley-Davidson in early 1936 — is a milestone motorcycle and one of the most important American bikes ever made. Yet up until the last minute, it was uncertain whether Harley would release the bike for sale. 

In the early days before World War II, Milwaukee-based Harley-Davidson sent test riders of new models out into the wooded hills of rural Wisconsin. The experimental models were unmarked, and testers were instructed to stay away from towns and dealerships. The point of all this secrecy was to keep the rumor mill down. The motorcycle world was very small, and even without the Internet or cheap, long-distance telephones, rumors would spread from one end of the country to another faster than a Twentieth Century Limited locomotive. In the case of the Knucklehead, the secrecy had an additional purpose: Harley didn’t want news of its new overhead valve engine to get out before its engineers had fixed its very leaky top end.

Beginnings of the sidevalve

For 1930, Harley-Davidson introduced an inlet-over-exhaust big twin to replace its aging sidevalve setup. Unfortunately, the new VL twins had multiple problems, resulting in a general recall and warranty replacement of expensive parts. Even with the repairs, the sidevalve engines were not as fast or reliable as desired, so Harley started looking for a replacement.

In August 1931, the Harley-Davidson board agreed to go ahead with development of a “sump oiler” motorcycle, meaning one with a recirculating oil system. Although most contemporary motorcycles including Harleys ran total-loss systems (lubricating oil was pumped through the engine and either burned or pumped out), recirculating oiling systems were being used in cars and in the top-of-the-line 4-cylinder motorcycles. A recirculating oil system added a little weight, but it increased performance and engine longevity. Archrival Indian was developing a dry-sump (oil in separate tank) recirculating lubrication system for its sidevalve twins, but the bike Harley was working on had a dry-sump oil system and overhead valves.

At the time, most motorcycles sold had sidevalve engines. Given the technology of the day and the developing state of metallurgy, not to mention the not-great oil, the easiest way to design a reliable, clean-running motorcycle was to put the intake valve next to the exhaust valve in a valve pocket, actuated by cam-driven lifters in the engine case. This was Indian’s solution, and the Indian Chief and Scout both had sidevalve engines. But sidevalve engines suffer from heat distortion and inefficiency, and they’re not inherently very efficient, although the Scout and Chief were reliable and fast.

Reliability is key

Fast and efficient overhead valve and overhead cam engines were certainly being designed and built, but most were intended for racing, where oily top ends, valve clatter and short intervals between major rebuilds were perfectly acceptable as long as the rider ended up on the podium. Harley’s plan was to build a bike that could be used every day by ordinary riders. If Harley could make the new design fast and reliable (reliability being key), it would have a major leg up over Indian.

By 1932, the Depression was affecting businesses all over America. Harley sales, almost 24,000 bikes in 1929, had decreased to 7,213 motorcycles over the 1932 model year. A major problem for Harley was the loss of its overseas markets, due to bad economic conditions worldwide and high tariffs put in place by countries trying to protect their home manufacturing. Harley slashed worker hours, laid people off and entered into a licensing arrangement with its Japanese affiliates, Alfred Rich Child and the Sankyo family. Harley agreed to furnish blueprints for its sidevalve motorcycles, and show the Sankyo family how to run a modern motorcycle factory. As a result, Harleys, made in Japan under the Rikuo trade name, could avoid the punitive tariffs, and the royalty fees kept Harley’s engineering staff working — and the overhead valve project going forward.

Harley-Davidson hit the bottom in 1933, with sales down to about 3,700 bikes. However, the overhead valve project continued to move along. Indian’s dry-sump engine debuted that year, giving a push to Harley’s development efforts. The first parts for the new model were cast around Labor Day, and bikes were assembled and turned over to testers. They discovered the top end leaked — a lot. William Harley, then the company’s chief engineer, had designed a lubrication system featuring an automatic oil supply to the valve rockers and valve stems. As originally designed, the new model had no return oil lines. It also didn’t have rocker covers, so once oil got to the rockers it had no place to go and escaped all over the engine and the rider’s pants.

Even so, through 1934 and most of 1935, Harley engineers stuck to the no-valve-enclosure system. The engineers tried to stop oil from leaking by metering the oil to the valves. It didn’t work. The engine was fast and reliable, but the dripping oil from the top end was a major problem.

The rumors continue

The annual Harley-Davidson dealers convention was set for November 1935. Despite management’s best efforts, rumors of the new overhead valve machine had circulated, and the ballroom of Milwaukee’s Schroeder Hotel was packed. Walter Davidson and William Harley raised the curtain on the new 61-cubic-inch overhead valve machine to cheers and applause. Although no demo rides were allowed, most of the dealers wanted one. Yet Harley was evasive on when the new model would be shipped; nobody wanted a repeat of the 1929 sidevalve debacle.

The first overhead valve models left the factory in March 1936, with the oil problem finally solved. Between the fall of 1935 and March 1936, Harley engineers designed a sheet metal cover the size of a baby food jar that fit over each valve stem. The covers were supplied with exterior oil lines that went to the rocker housing. Engine vacuum drew oil back into the breather valve, which blew oil onto the camshaft. The fix worked — the new bike leaked no worse than any other two-wheeler of its time.

The overhead valves were not the only feature of the new model, which came in two versions: the standard E model with 6.5:1 compression and the EL sport version with 7:1 compression. The low compression ratios reflected the not-great gas of the time and were also intended to not put excessive stress on the untried bottom end. The engine also featured a newly designed clutch, a new 4-speed constant-mesh transmission instead of the old 3-speed, and dry-sump lubrication with the oil carried in a separate tank instead of in a section of the gas tank, as in prior models.

Bore and stroke were 3-5/16 x 3-1/2 inches. Many fast 1920s machines had long strokes against smaller bores (termed “under-square”), but developments in the 1930s proved the value of more nearly square engines, with more equal bore-to-stroke dimensions. Valve angles were 90 degrees set in a hemispherical combustion chamber, and the four cam lobes spun on a single camshaft, aiding accurate valve timing. Claimed horsepower of the EL sport model was 40 horsepower at 4,800rpm.

The frame and forks were also new. Instead of the drop-forged I-beam springers used on the sidevalve bikes, the overhead valve models sported stylish, extruded tubular forks, still with twin legs and leading links. The double-downtube frame had single-butted, double-diameter downtubes. Given the bad roads of the day, and the propensity of contemporary riders to go offroading on their motorcycles, the frame was a little light. Late 1936 frames had a clamp bracket brazed to the frame to support the kickstart side.

Moving ahead in style

The styling, pure Art Deco, was beautifully done. The instrument panel on top of the tank was a new idea, and was artistically executed. The oil tank was designed to fit around the battery, which had the side effect of containing any battery acid mist. The bike’s lines flowed smoothly from the curving front fender to the pointed taillight. Standard two-tone paint combinations were Sherwood green with cream, teak red with black, dusk gray with royal blue, Venetian blue with Croydon cream, and maroon with Nile green. Chrome was just beginning to be phased in, so many parts that would be chromed today were instead either painted in one of the tank colors or black. The price was $380, which in today’s dollars would be about $6,500. Not bad for a large capacity, fast motorcycle. Dry weight was 515 pounds — again, not bad for a large capacity, fast motorcycle.

Yet Harley engineers were not 100-percent satisfied with the bike. Dave Kafton, a Harley restoration expert, says that almost every part was changed, either during the model run or right afterwards. “There are lots of one-year-only parts, and most are made of unobtanium,” Kafton says. Although only 1,704 Es and ELs were built during that first year, changes during 1936 included three different timing covers and two different kickstarter gearing combinations. The pinion gear shaft was revised to improve oil mileage. Three sets of oil tanks and oil line fittings were tried out. The rocker arm shaft covers changed, and the nuts securing them got larger. The ignition timing was advanced, and the frame supports for the gearbox were beefed up.

By this time the economy was on the upswing, and so were Harley’s sales. For 1937, Harley continued building its 45-, 74- and 80-cubic-inch sidevalve models, but they were restyled to look like the overhead valve models, with a beefed-up version of the double-downtube cradle frame introduced in 1936 now used for both the sidevalves and the EL. Harley cut costs by interchanging parts between the 61-cubic-inch overhead, the 74-cubic-inch sidevalve and the 80-cubic-inch sidevalve. All three sidevalves now had dry-sump lubrication. For the 1937 model year sales were up to 11,674 motorcycles. Harley-Davidson had survived some very tough times.

It wasn’t a Knuckle then

Back then, nobody referred to the overhead valve Harley as a Knucklehead. If you clench your fist and look at the back of your hand, the knuckles are the polished rocker arm nuts with the tendons on your hand the pushrod tubes. The nickname first appeared after World War II, after Harley-Davidson came out with a new top end for its twin, now known as the Panhead.

Back in the 1930s, motorcycle owners took care of their bikes, but they didn’t baby them. The same machine that took the owner to work during the week also took him — or her — out touring, or hill climbing or enduro racing on weekends. Hard use and the inevitable crashes took their toll, and not many of the original 1936 Knuckleheads have survived. No one is exactly sure how many exist and are still in running condition.

Our feature bike is one of the rare survivors. It was restored by Antique Motorcycle Club of America judge Jim McLean, now sadly passed on. It’s currently owned by Don Hart of Canada. It runs well, and despite its value and rarity, Don rides it in sheltered conditions. “It feels much lighter than it is,” Don says, adding, “It feels lighter than my 1920s JDH and it sounds really good. The handshift transmission on this bike works very well. The gears are marked, and getting it into gear is not difficult. It’s the most important bike in my collection, and it’s also my favorite.” Looking it over, it’s not hard to see why.

A big thank you and a tip of the helmet to Dave Kafton for technical assistance. MC