Twin Cam engine (Harley-Davidson)

From Wikipedia, the free encyclopedia

The Harley-Davidson Twin Cam 88 engine was released for the 1999 model year in September of 1998. The engine was a successor to the Evolution engine ("Evo"). The engine design differed considerably from its predecessor the "Evo" although shared some design elements with the Sportster line. The 88 represents the displacement of the standard engine in cubic inches. 88 cubic inches equals approximately 1450 cc. The motor company released a "95 inch" upgrade kit a year later to increase the displacement to 1550 cc. The Twin Cam, however, wasn't initially used in the Softail model family before the year 2000, because of the chassis' design and also because of increased engine vibration. Harley then solved the issue by making a redesigned version of the Twin Cam, the Twin Cam 88/96B, which is essentially the same as the original Twin Cam, but with a different engine block design and twin chain-driven counter-balancers, which had caused some controversy among Harley veterans, claiming that the "Harley vibes" were a part of their motorcycles.

[edit] Differences to predecessor (Evolution engine)

The 96 cubic inch variant of the Twin Cam, currently used in most Harley-Davidson motorcycles.

The Twin Cam generated considerably more horsepower and torque than the Evo. All components were also built to tougher standards. Upgrading to 1550 cc became the norm among most enthusiasts.

When the Twin Cam engine was released, Harley-Davidson put much emphasis on the supposedly stronger case and bottom end. They claimed the older Big Twin design, with the cam bearing positioned directly above the main bearing on the right side of the engine, precluded increasing main bearing size to optimal and created structural weakness in the right side case because of the small space between the two bearings. However, after market companies have successfully used the old design in engines displacing 144 cubic inches (2360 cc) and more, producing well over 120 foot pounds (163 Nm) of torque and 120 horsepower (89 kW) without case failure, casting doubt on Harley-Davidson's claims.

When the Evolution Big Twin engine was released, Harley-Davidson did not protect its design elements as thoroughly as they have with the Twin Cam. In fact, H-D relied on the third-party firms to add value to their products and broaden their appeal. Since the Evo's release in 1984, though, the company has moved to catalogue thousands of accessories, including engine upgrades. The company moved to the Twin Cam not because the Evo had reached its power limits as a design, but because H-D could not prevent other manufacturers from making virtual clones of the design. With the Twin Cam, H-D was able to preempt cloning via the U.S. Patent Office, thereby making it a lot more difficult and expensive for the after market to compete with the Motor Co. in the development and sale of upgrades or complete motors.

[edit] Wear of cam tensioner shoes

The Twin Cam motor has cam chain tensioners with nylon composite shoes, and these have proven to be a wear item even though they are not on the regular maintenance schedule. Some riders have seen these shoes wear down until there was metal to metal contact against the cam chain, while others have experienced no wear. Harley-Davidson changed from spring loaded to hydraulically loaded tension on the shoes in the Dyna line for the 2006 model year and for all Twin Cams with the introduction of the 96ci Twin Cam for the 2007 model year. Some believe shoe wear and the variability of cam timing introduced by inconsistent tension on the cam chain continue to be an issue best resolved by after market gear drive cam sets (S&S and others).

[edit] See also