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Harley-Davidson Engine Timeline: Big Twins

For more than 100 years, Harley-Davidson has been producing its legendary lineup of Big Twin engines. Through the decades, various technological advances have led the company to develop nine different types of basic Big Twin motors.

Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins Harley-Davidson Engine Timeline: Big Twins

 

F-Head

Harley-Davidson F-head. 1914-1929 - Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins Harley-Davidson F-head. 1914-1929

The original Harley Big Twin engines, the F-Head models were IOE, or intake/inlet over exhaust- type motors. These simple yet powerful engines were available in 61 cubic inch and 74 cubic inch sizes, and were produced from 1914 through 1929. 

1915 Harley-Davidson F-Head. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins 1915 Harley-Davidson F-Head.

Flathead

Harley-Davidson Flathead.  Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins Harley-Davidson Flathead.

Named for its flat-topped, vented cylinder heads, the side valve-equipped 45 cubic inch flathead engine debuted in 1929, and the 74 cubic inch V model Big Twin came out in 1930. The Big Twin model was built in part to compete with the 74 cubic inch Indian Chief.

In 1937, the U series of Harley-Davidson flathead Big Twin engines made their debut, replacing the V series. The U and UL models featured 74 cubic inch powerplants, and the UH and the ULH models were outfitted with 80 cubic inch engines. The 80 cubic inch models were produced until 1941, and the 74 cubic inch U and UL models were in production until 1948. 

The three-wheeled Harley-Davidson Servi-Cars made from the early 1930s through 1975, were powered by flathead engines during their entire run of production. 

Jeff Leighton's 1942 Harley-Davidson Flathead. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins Jeff Leighton's 1942 Harley-Davidson Flathead.
Jeff Leighton's 1942 Harley-Davidson Flathead at Born Free 8. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Jeff Leighton's 1942 Harley-Davidson Flathead at Born Free 8

Knucklehead

Harley-Davidson Knucklehead. 1936-1947 Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson Knucklehead. 1936-1947

Made from 1936 through 1947, the Harley-Davidson Knucklehead motor was Harley's first production bike to have overhead valves. A more-efficient circulating oil lubrication system on the knucklehead replaced the "total-loss" lubrication system that previous models featured. Also known as the EL model, the knucklehead got its name from its rocker boxes that looked like knuckles on a human fist. Both 61 cubic inch and 74 cubic inch models of this Big Twin engine were produced by Harley-Davidson. 

Details on Jesse Basset's Knucklehead - The Gasbox. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Details on Jesse Basset's Knucklehead - The Gasbox.
Buddy Miller's 1947 Knucklehead. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Buddy Miller's 1947 Knucklehead.

Panhead

Harley-Davidson Panhead. 1948-1965 - Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson Panhead. 1948-1965

This Big Twin engine gets its name from the distinctive cake pan-like appearance of the rocker covers. Available in 61 cubic inch EL and 74 cubic inch FL and FLH models, this engine was produced from 1948 through 1965. The Harley-Davidson Panhead was equipped with aluminum heads and hydraulic valve lifters, and the 1965 Electra Glide model brought about the introduction of electric starters on Harley-Davidsons. The Panhead is widely considered to be the most attractive of all Harley-Davidson Big Twin engines.

Detail shot of Kerry Sayre's 1959 Duoglide. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Detail shot of Kerry Sayre's 1959 Duoglide.
Max Schaaf's Harley-Davidson Panhead. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Max Schaaf's Harley-Davidson Panhead.

 

Shovelhead

Harley-Davidson Shovelhead. 1966-1984 Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson Shovelhead. 1966-1984

Produced from 1966 until 1984, the Harley Shovelhead engine was available in 74 cubic inch and 80 cubic inch models. The Shovelhead was designed in part to produce more power and higher performance to make up for the increased weight of new Harley-Davidson motorcycle models.

This Harley-Davidson Big Twin motor also gained its name because of the appearance of the rocker covers. Somewhat resembling the knucklehead, the slightly rounded Shovelhead rocker box covers are reminiscent of small shovels, with the push rod tubes serving as handles.

Detail shot of Bob Millerleile's PanShovel. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Detail shot of Bob Millerleile's PanShovel
Mikey Revolt's 1977 Harley-Davidson Shovelhead. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Mikey Revolt's 1977 Harley-Davidson Shovelhead.

Evolution

Harley-Davidson Evolution. 1984 -1999- Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson Evolution. 1984 -1999

With the Evolution engine, Harley-Davidson had an engine that not only evolved from the Shovelhead, but was very different, and technically superior in a number of ways. The Harley Evo was not only more powerful, but it ran cooler and smoother than the Shovelhead. The 80 cubic inch Evolution motor was produced between 1984 and 1999. 

Tim Stat's Harley-Davidson 1992 Evolution FXR at Fuel Cleveland 2016. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Tim Stat's Harley-Davidson 1992 Evolution FXR at Fuel Cleveland 2016.

Twin Cam

Harley-Davidson Twin Cam. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson Twin Cam.

In 1998, Harley-Davidson introduced the eighty-eight cubic inch Twin Cam engine for the 1999 model year, and continued production of different Twin Cam models until 2016. A 96 cubic inch Twin Cam model, as well as a 103 cubic inch, and a 110 cubic inch model were also produced. This model was named for the two chain-driven cams it contains. The Twin Cam 88B engine was a counter-balanced Twin Cam 88 motor that was designed to fit Harley-Davidson Softail models. 

The Twin Cam engine provided more torque and horsepower than the Evolution model, and was originally available with a choice of carburetor or fuel injection.

Issues with oil circulation on the Evolution engine prompted Harley-Davidson to outfit the Twin Cam with a better-performing internal twin-gerotor oil pump.

The Twin Cam motor offered higher compression than its predecessor, and a dual-coil ignition system that eliminated wasted spark.

Norm Betts on his Twin Cam at Fuel Cleveland. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Norm Betts on his Twin Cam at Fuel Cleveland.

Revolution

Harley-Davidson Revolution.  Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson Revolution.

In place of the familiar 45-degree V-Twin engines that Harley is known for, the Revolution engine is a liquid-cooled 60-degree V-Twin powerhouse. This engine has been standard equipment on Harley-Davidson's cruiser/muscle bike, the VRSC, or V-Rod since 2001. Originally available as a 69 cubic inch dynamo, the Revolution was beefed-up to 76 cubic inches in 2008.

Designed to provide competition to both imported and domestic popular street/cruiser bikes, the Revolution engine is actually a collaborative effort between Harley-Davidson and Porsche. 

Vror 2016 model.  Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Vrod 2016 model.

Milwaukee-Eight

Harley-Davidson Milwaukee Eight. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson Milwaukee Eight.

In 2016, Harley-Davidson announced that all 2017 touring and trike motorcycle models would be equipped with their new Milwaukee-Eight engines. These new Harley-Davidson Big Twin motors include a 107 cubic inch model, a liquid-cooled version of the 107 cubic inch machine, and a 114 cubic inch, liquid-cooled model.

The Milwaukee-Eight engine features Harley's traditional 45-degree V-Twin design. The engine provides more torque and overall power than previous models, and is counter-balanced to reduce vibration.

Each cylinder utilizes two spark plugs, and each cylinder head contains four valves, that increase the capacity of the intake and exhaust flow. A development objective of providing a cooler-running machine, has been achieved by the inclusion of an improved heat management system.

Harley-Davidson's latest big twin motor release surprised everyone. Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. Harley-Davidson's latest big twin motor release surprised everyone.
It's not a chopper yet... Lowbrow Customs - Harley-Davidson Engine Timeline: Big Twins. It's not a chopper yet...

The various types of Big Twin engines manufactured by Harley-Davidson through the years have revolutionized the motorcycle industry. If history is any indicator, Harley-Davidson will continue to blaze new paths with these amazing engines well into the future. 

2 thoughts on “Harley-Davidson Engine Timeline: Big Twins”

  • Nice history lesson and pictorial, my favorite looking harley engine has to be the knuckle and pan. Having owned most model Harleys, engine wise, other than sportsters and 74 inch flat heads. My fondness for the flatside shovelhead engine has remained high for the last 45 years. They run great ànd last forever, if looked after properly, I rode one, a1967 from Ottawa Canada to Vancouver BC down to California and back. A few issues but nothing I couldn't handle, the journey took 5 months, I rebuilt the engine when I got back sold it, the dude I sold it to passed it on to his son and it's still on the road last I heard. Great engine, I have a 1990 FXST, Hardtailed by Fabricator Kevin, with a 1980ish shovelhead with a S&S topend also a great engine

    Reply
  • I disagree with the Revolution engine being included as a Big Twin. This engine was developed solely as a Superbike racing engine, with a displacement limit of 1000cc, and no relationship to any Harley streetbike engine. It was a successor to racing engines based on Sportster engines, which are also not considered to be Big Twins. All Harley Big Twins are 45 degree, air-cooled V-twin engines, and all are OHV engines, except for the 74 and 80" Flathead bikes of the 30s and 40s.
    I also think most people consider the Knucklehead to be the best-looking Big Twin.

    Reply
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