The Harley Davidson Fatboy
The Harley Davidson Fatboy is equipped with the iconic Twin Cam engine, a significant evolution in Harley's motorcycle engine lineup. This article delves into the technical aspects and history of the Fatboy and its engines.
Introduction to Harley Davidson Engines
Harley Davidson’s Twin Cam engines, introduced around 1998, marked a significant departure from the Evolution engine, which had been based on a single camshaft and overhead valve motors first introduced in 1936. The new Twin Cam engine presented key differences in design and performance while maintaining a core resemblance to earlier Harley engines.
Design of the Harley Davidson Fatboy Engine
The Harley Davidson Fatboy features a V-twin engine with cylinders set at a 45-degree angle. This engine, like many others from Harley, is air-cooled and utilizes pushrods and active valves. The camshaft has a single-pin arrangement, much like a knife-and-fork configuration of the connecting rods, which are sandwiched between a pair of flywheels.
The Twin Cam 88 and Twin Cam 96
The Twin Cam 88 engine was released in September 1998 for the 1999 Harley Davidson model. Later, the Twin Cam 96 engine, designed for the 2007 Harley Davidson motorcycles, came with slight modifications to improve performance and reliability.
Chassis Design and Vibration Management
Initially, the Fatboy was not used in the Softail model due to issues with vibration transfer. The chassis design of the Softail bike caused vibrations to directly transfer to the frame, which was not the case in the Dyna models, where vibrations were dampened by rubber mounting. This made the Fatboy a less favorable choice for the Softail line before 2000.
Transmission and Engine Mounting Issues
The Fatboy’s engine and transmission are directly bolted together, which causes interference with the Softail frame and seat post. Harley Davidson addressed this issue by designing a new engine variant with an improved engine block. This modification allowed the chain drive balance shafts to run smoothly, solving the mounting problem.
Updated Engine Versions and Adaptations
The updated engine variants were released in time for the 2007 model year and were equipped with Softail models. The 103 ci engine eventually replaced the previous version, though third-party adapters allow the older Twin Cam motors to be mounted to Softail models produced before 2000.
