Harley Davison V-Twin Engine Overview and History

In the early 1900’s, a young Harley-Davidson motor company developed
the classic V-twin engine in a quest for more power and reliability.
Theoretically, two cylinders meant twice as much power; and if one
cylinder failed, the rider still had one more to get him or her to the
destination.

Documents prove William Harley and the Davidson brothers Arthur and
Walter had a working V-twin by 1907. However, they grappled with valve
issues until refining the motor in 1911. The initial and all subsequent
V-twins for over 100 years, had cylinders offset by 45 degrees, an
arrangement thought to have been used because this allowed the motor to
fit nicely into the early vehicle’s frame. The size of the motor, 61
cubic inch displacement, was thought at the time to be the ideal size
for a motorcycle engine. This size was also conveniently picked because
two of the single cylinder heads the company was using could be put
together for use on the new motor, and the size worked out to be an
even 1000 cc.

The early V-twins put out six or seven horsepower, which was
adequate for the slower speeds and almost non-existent highways of the
time. The 74 cubic inch V-twin introduced in 1921, packed 18
horsepower, more than double the previous version, and was to be used
for highway travel and especially for sidecar use, as advertised. This
motor remained unchanged through 1929. In 1930, the company introduced
a new V-twin which was immediately subject to many problems, including
flywheels that were too small and too little power. An 80 cubic inch
side valve and 61 cubic inch V-twin was manufactured from 1936-into the
1950’s, when the upgraded 45 and 55 cubic inch V-twin came out. These
were called “panhead” motors and were available into the 1960’s.
Nineteen fifty-seven saw the introduction of the Sportster with its 883
cubic inch V-twin. In the mid-1960’s, Harley-Davidson introduced the
larger 74 and 80 cubic inch V-twins that powered the Electra-Glides and
Super Glides into the 1970’s and 80’s. The current overhead valve
Evolution V-twin has aluminum cylinders and heads, while the current
twin cam 88B is counterbalanced. And a new liquid cooled, 60-degree,
four stroke, four valve per cylinder V-twin powers the attractive V-Rod.

H.D. V-Twin Engines

61 c.i. V-Twin (1911-1921)

74 c.i. V-Twin (1921-1929)

74 c.i. “VL” V-Twin (1930-1940)

80 c.i. Side Valve V-Twin (1936-1945)

61 and 74 c.i. Overhead Valve “Knucklehead” V-twins (1936-1947)

45 and 55 c.i. K-model V-Twins (1952-1956)

61 and 74 c.i. Overhead Valve “Panhead” V-Twins (1948-1965)

883 c.c. and 1200 c.i. XL V-Twins (1957-present)

74 and 80 c.i. “Shovelhead” V-Twins (1966-1983)

Evolution V-Twin (1984-1997)

Twin Cam 88 and 88B (1998-present)

Liquid-Cooled V-Twin (2002-present)