You May Not Want A Used Harley-Davidson With This Engine (For A Number Of Reasons)

There are certain sounds in motoring that are as iconic as the machines that generate them. Typically, V8s will produce such sounds, as well as engines from one of the most iconic motorcycle brands: Harley-Davidson. The brand's V-twin engines, in particular, are known for producing an iconic throaty "thrump" often referred to as a "potato" sound. The engine's lineage stretches back to the company's first V-Twin engine, which made its debut in 1909 and produced a modest 7 horsepower. Since then, the engine has evolved through multiple generations. In 2016, these evolutions led to the development of the Milwaukee-Eight (M8), which came out in the 2017 model year. 

When Harley-Davidson introduced the M8, it was the first major redesign of the twin-concept since the Twin Cam 88 was introduced in 1999. However, initial engine models could be problematic and developed a reputation for oil-related issues. More specifically, engines built between 2017 and 2019 were prone to problems, with the vast majority affecting the oil system. The problems didn't affect every engine, but many owners did report problems with the Milwaukee-Eight 114. Ultimately, they were significant enough for Harley-Davidson to publish service bulletins and revise key elements of the engine's oil system. This is why buyers considering a used Harley with an early M8 engine will want to proceed with caution. Let's take a closer look at the problems with early M8 engines. 

The oil-related issues with the early versions of the M8 engines weren't about leaks or poor build quality. They mainly had to do with how oil moved through the engine under certain conditions. In some 2017-2019 models, riders reported symptoms of something called oil sumping. This occurs when oil is not efficiently returned to the oil tank and instead accumulates in the crankcase. 

When that happens, excess oil can increase crankcase pressure and interfere with normal engine function. If this happens, the problem can manifest itself in several ways, including raised engine temperature, rough idling, high levels of engine braking, power loss, and oil aeration as the flywheels rotate in the excess oil. The issue was most commonly reported on Touring models and Softails. Motorcycles that were ridden hard or used for longer journeys were more prone to it as well. Without remedial action, the condition can cause serious engine damage. 

Another oil-related issue affecting 2017-2019 M8 engines was caused by transmission oil migrating into the primary housing. The result of this was low transmission oil levels and correspondingly higher primary oil levels. In response, Harley-Davidson introduced a series of hardware revisions. These included an updated oil pump and venting improvements, which aimed to improve oil flow and efficiency. By the 2020-2021 model years, these improvements had largely addressed the problem, and reports of oil sumping dropped off significantly.