| Specification | Value |
|---|---|
| Engine | Milwaukee-Eight 114 (1,868cc) |
| Oil Type | HD 360 20W50 / Syn3 20W50 |
| Oil Capacity | 4.7 Liters (5.0 Quarts) |
| Front Tire | 160/60R18 70V |
| Rear Tire | 240/40R18 79V |
| Spark Plug | Harley-Davidson 6R10 (Gap: 0.76–0.89 mm) |
| Battery | Part No. 66000207 |
While the Harley-Davidson Fat Boy achieved cinematic immortality in 1991’s Terminator 2: Judgment Day, the modern FLFBS (114 CUI) variant represents the most significant engineering evolution in the model’s history. Introduced in 2018, this iteration abandoned the traditional Softail counterbalanced Twin Cam setup for a lighter, stiffer frame and the high-torque Milwaukee-Eight powertrain, fundamentally changing the bike’s center of gravity and lean angle capabilities.
Engineering Deep Dive: The Milwaukee-Eight 114
The heart of the FLFBS is the 114 cubic inch Milwaukee-Eight engine. Unlike previous generations, this powerplant utilizes a four-valve per cylinder head design, which increases intake and exhaust flow capacity by 50%. This configuration, combined with dual spark plugs per cylinder, ensures more complete combustion and thermal efficiency. For the Fat Boy, this translates to 155 Nm of torque peaking at a low 3,000 RPM, providing the massive roll-on power required to move its signature Lakester cast aluminum wheels.
Maintenance & Fluid Dynamics
From a technical maintenance perspective, the FLFBS demands precision. The lubrication system requires 4.7 liters of 20W50 oil. MotoSpecsLab recommends the Screamin’ Eagle Syn3 for riders in high-temperature climates to maintain viscosity under the heavy thermal load of an air/oil-cooled V-Twin. The ignition system relies on 6R10 plugs; maintaining a precise gap of 0.76–0.89 mm is critical to prevent hesitation under high-load acceleration.
Chassis and Contact Patch
The Fat Boy is defined by its massive tires. The 160mm front and 240mm rear setup is the widest ever offered by the factory. To maintain neutral handling and prevent ‘cupping’ of the tread, tire pressures must be strictly monitored at 36 psi (front) and 42 psi (rear). The 2018+ Softail frame also features an under-seat mono-shock with easy hydraulic preload adjustment, allowing riders to tune the suspension geometry based on passenger or luggage weight.
Technical FAQ
What is the battery requirement for the FLFBS?
The model utilizes the high-cranking 66000207 battery, designed to handle the high-compression start-up requirements of the 1,868cc engine.
How often should I check the spark plugs?
We recommend inspecting the 6R10 plugs every 8,000 km (5,000 miles) and ensuring the gap remains within the 0.76–0.89 mm specification to ensure optimal firing intervals.