When searching for a used Touring or Softail, the first question rarely revolves around color or saddlebags. It focuses on the engine. Twin Cam 103, Milwaukee-Eight 107, 114, or 117: each displacement corresponds to a design era, a level of torque, and very different field feedback. This article reviews what we really know about their endurance, without fantasy or dealership rhetoric.
Why mileage makes all the difference in this comparison
The Twin Cam 103 has been on the roads of Europe and North America for over ten years. Owners display several hundred thousand kilometers on the odometer without heavy intervention on the bottom end. This mileage provides a clear picture of its strengths and weaknesses.
For the Milwaukee-Eight 107 and 114, the first systematic reports of engines exceeding 80,000 to 120,000 km began to emerge from 2022. According to surveys reported by Motorradmagazin and PS Magazin (covering the period from 2015-2018), the large Harley-Davidson twins show an average first major service interval between 120,000 and 150,000 km with regular maintenance. These data mainly cover the Twin Cam and the early Milwaukee-Eight models.
The 117, however, presents a different problem. Long reserved for CVO editions, it has become widespread across all Harley cruisers since 2022-2024. A video comparison featuring a 2009 TC96, a 2017 M8 107, and a 2024 M8 117 states it bluntly: no documented data exists for the 117 beyond 100,000 miles.
The engine is too new to assess its longevity at the same level as its predecessors. Comparing an article that delves into the reliability of Harley engines from 103 to 117 allows for cross-referencing field feedback before any purchase.
Twin Cam 103: known wear points after ten years of mileage
The 103 cubic inches (1,688 cm³) is an engine that mechanics know by heart. Its Twin Cam design, with chain-driven camshaft on models prior to 2007 and then gear-driven afterward, has generated two very distinct generations of feedback.
Chain tensioners and compensator
On chain-driven Twin Cams, the hydraulic tensioner is the first point of monitoring. A cold start rattle usually indicates its wear. Replacement with a mechanical tensioner (gear drive conversion) has become a standard practice in workshops.
The primary compensator, which absorbs the jolts of the 45-degree V-twin, can also show play beyond 60,000-80,000 km. A rattling noise at idle does not always indicate a serious problem, but it deserves a precise diagnosis.
What holds up well on the 103
The bottom end (crankshaft, connecting rods, bearings) withstands high mileage remarkably well if oil changes are adhered to. Feedback from high-mileage owners converges on this point: the 103, with standard maintenance, is a durable engine whose weaknesses are localized and documented.
Milwaukee-Eight 107 and 114: what the first high mileages reveal
The switch to Milwaukee-Eight in 2017 changed many things under the hood. Four valves per cylinder instead of two, oil cooling (or liquid cooling on some Tourings), a single chain-driven camshaft, and a completely rethought distribution system.
- The removal of the compensator on the M8 eliminates a recurring weak point of the Twin Cam. The primary drive system is simpler and more reliable in the long term.
- Improved cooling reduces overheating issues in urban traffic, a known flaw of Twin Cams in the city during hot weather.
- The single chain-driven distribution with hydraulic tensioner remains a point of monitoring, but feedback so far shows fewer cases of premature failure than on older chain-driven Twin Cams.
Have you heard that the M8 107 lacks torque compared to the 103? In reality, the 107 delivers higher torque thanks to its four valves despite a comparable displacement (1,745 cm³ versus 1,688 cm³). The difference is especially felt in mid-range acceleration.
The 114 (1,868 cm³) shares the same architecture. The question that often arises on forums concerns the difference between the 2017 114 CVO and the standard 114 that appeared in 2018-2020. The mechanical base is identical. The differences lie in the injection mapping, exhaust, and sometimes the air filter, not in the robustness of the engine block.
Harley 117 engine: increased power, decreased mileage
The 117 (1,923 cm³) represents the top of the Milwaukee-Eight range. With its increased stroke and bore, it offers a noticeable boost in torque, especially for loaded Tourings.
The widespread availability of the 117 since 2024 far exceeds the CVO circle. All cruisers in the Harley-Davidson range can now benefit from it. This democratization means that thousands of additional engines are accumulating kilometers, but none yet have the mileage history of a 103 or even a first-generation 107.
This gap between commercial distribution and longevity data creates a concrete area of uncertainty for the buyer. The 117 adopts the proven M8 architecture, which is reassuring. The materials and tolerances have been adapted to the increased mechanical stresses associated with the larger displacement.
Points to watch on a recent used 117
- The maintenance history takes precedence over everything else. A 117 with oil changes spaced beyond the manufacturer’s recommendations loses its main guarantee of longevity.
- The cylinder head gaskets and cooling system deserve special attention on the partially liquid-cooled versions (Twin-Cooled), as the increased complexity adds potential leak points.
- The original injection mapping can be conservative. Many owners install a reprogramming module, which alters the thermal stresses on the upper engine.
Which Harley engine to choose based on your actual usage
A buyer looking for a Touring to cover miles year-round with a controlled budget will find in the 103 an engine whose flaws are well-known and parts readily available. The 103 remains the most predictable choice in the used market for intensive use.
The 107 and 114 offer better riding comfort thanks to the Milwaukee-Eight design, with enough mileage history to provide reassurance. The 114 provides a significant advantage in acceleration without altering the overall reliability of the engine block.
The 117, for its part, appeals with its generous torque and premium positioning. Buying a recent used 117 amounts to betting on the strength of the M8 architecture without having the same mileage history as the other engines. Checking maintenance and limiting undocumented modifications remains the best strategy, regardless of the engine chosen.
