5 Of The Most Reliable Harley-Davidson Engines Ever Built (According To Owners)

There are numerous ways to describe an engine. You can distinguish the best overall Harley Davidson engines, but constructing a list of the most reliable Harley engines is a different exercise in measuring longevity. Nonetheless, many of the engines on this list overlap with our picks for the best overall Harley engines simply due to their well-rounded designs. Perhaps reliability is an unintended consequence of power and speed, and fans of collectible Harleys will likely find their top choices among our most reliable picks as well. But whatever your approach to judging a motorcycle engine may be, there are some unavoidable criteria for deciding the best of the best.

Our choices for this list are a bit more specific than those on our list of the best overall Harley engines. For example, the Milwaukee-Eight engine has been released in several different volumes — with 107, 114, 117, and 121 cubic-inch engines implemented in numerous Harley models. And for this list, we awarded the Milwaukee-Eight 114 the best-reliability accolade, since it's the engine found on the wildly successful 2018 Harley-Davidson Fat Bob FXFB. 

Our methodology in creating this list involved combing through owner reviews to discover the most commonly-cited engine models for their longevity. Power is still important, since a reliable engine should deliver its expected horsepower without fail. Secondly, determining reliability means a lower frequency of problems. If an engine has a pattern of complaints on sites like Motorcycle Reviews, it probably wasn't a worthy choice for this list. 

The Twin Cam line of Harley-Davidson engines was introduced in 1999, starting with the Twin Cam 88. Within a few years, the Twin Cam 103 emerged, increasing the torque of its predecessors. The new design quickly gained a reputation for incredible reliability, landing it on the list of the best Harley motorcycle engines ever, as well as the list of the most reliable motorcycle engines ever. Unsurprisingly, Harley began implementing this wildly successful engine in numerous new motorcycle models. 

The 103cc Twin Cam reached new heights of power. It delivered roughly 100 lb-ft of torque and 85 horsepower, with some variability depending on the motorcycle model. Since its introduction around 2011, it can be found in the Touring, Softail, and Dyna lines, among a few others. In terms of reliability, owner reviews sing the Twin Cam 103's praises almost universally. We can use the 2014 Harley-Davidson Dyna Low Rider as a case study. 

The 2014 Harley-Davidson Dyna Low Rider was the first in its line to incorporate the Twin Cam 103 engine, and it was a success. On Motorcycle.com, it scores a ranking of #2 out of 14 for Harley Cruisers, based on customer reviews. Here, owners say that the bike is "easy to handle in the curves," with others saying it's "quick and nimble." The result is a 4/5-star rating. 

Other sources support the praise. The responses on Harley-Davidson Forums to the question, "Is the 103 a good engine?" are overwhelmingly positive. One user says their 2007 Dyna has hit 106,000 miles and still performs perfectly, another put "45,000 trouble-free miles" into their 2012 TriGlide 103, and another states they "rode a 103 Heritage for 51K miles... [without] a single problem."

Harley-Davidson's entry on the list of the most reliable motorcycle engines that reviewers swear by is the Evolution engine — and for good reason. The Evolution (or "Evo") is the engine behind many of the most well-received Harley models to date, including the Sportster, Fat Boy, and Softail Custom, which comprise many of the best Harley-Davidson motorcycles. To say it's a popular engine is an understatement. 

However, the 883cc version is the most reliable out of all the Evolution sizes. Using the Sportster 883 Iron's run from 2015-2021 as a test subject, the consensus among owners is positive. On Motorcycle News, it scores an incredible 4.8/5-star rating from owner reviews. Specifically, its "Owner's Reliability Rating" is a perfect 5/5, meaning any issues fall within other domains. One owner gives it a 5/5 star rating for "Reliability & build quality," while many seem to laud its affordability for such ample torque and power. 

Such customer reviews paint a clear picture. The Evolution 883cc engine is a reliable and fairly powerful motorcycle engine that delivers the goods. The wide variety of models for which the 883 Evo empowers further adds to its appeal as a versatile and reliable high-torque engine. It's the kind of engine you'll only find among American-made Harleys.

Yes, there's a Harley engine called the "Evolution," and one called the "Revolution," so they're easy to mix up. However, the two models are quite distinct. The Revolution was first introduced in 2001 with its use in the V-Twin Racing Street Custom models. Most unique to this new engine was its liquid cooling and fuel injection, making it most appropriate for fast-shifting, high-acceleration street riding. Nonetheless, a few famous cruisers employ the Revolution engine as well, such as the VRSCDX Night Rod Special. Not only is the Night Rod Special found on lists of the most reliable Harleys ever, it's also considered one of the most stylish.

Flashy style is one thing, but reliability is just as important. Owner experiences suggest that the Revolution X engine seems to be the most well-received out of the Revolution variants. For instance, we can use the Harley-Davidson Street 750 as a case study. Motorcycle News shares owner reviews of the Street 750, and they're largely positive — with reliability standing out as one of the bike's strengths. 

One owner writes, "I have had it for 2 years — no issues, reliable, and it is nice and simple to ride." Two years isn't an eternity, but such reliability seems to emerge regardless of the time frame. For instance, another owner says, "You can wreck this thing and it just keeps going." We don't necessarily advocate wrecking your Street 750 motorcycle, but such user trials point towards a robust and reliable engine design. Some customers noted issues with braking — likely related to an NHTSA recall — but from an engine reliability standpoint, the consensus is positive.

The Milwaukee-Eight is famous among Harley-Davidson fans. It was essentially an unofficial upgrade to the Twin Cam line of engines, with the addition of two extra valves per cylinder, among other power boosts that lead to around 10% more torque in higher rev ranges. This high-torque beast can be found on iconic Harleys like the 2018 Harley-Davidson Fat Bob FXFB, the CVO Street Glide models, and many of the most recent Harley trikes and touring bikes. 

Besides being one of the biggest motorcycle engines ever, the Milwaukee-Eight 114 handles its bulk well. Its liquid-cooling helps give the famous Ultra Limited and Road Glide Harleys their power, while one of the latest models to employ it is the 2024 Harley-Davidson Street Bob 114.

Customer reception to the Milwaukee-Eight is overwhelmingly positive. Using the 2018 Fat Bob 114 as a case study, on Motorcycle News, owner ratings for the engine average out at 4.1/5. It's not perfect, as customers noted other issues with the bike's build quality and lackluster brakes, but it's nonetheless a solid score for such a massive engine. One user writes, "There were no breakdowns in my ownership," while another says, "the Milwaukee-Eight marked a huge step forward over the old Twin Cam ... as well as better reliability."

The Revolution Max 1250 engine is undeniably powerful. Introduced in 2021, its stand-out models include the Pan America 1250 adventure-touring bike and the Pan America 1250 Special — two motorcycles that demonstrate the latest in Harley-Davidson's drive for power. Liquid-cooled, V-Twin cylinders, and "low-end torque" deliver smooth throttle control. According to Harley-Davidson Chief Engineer Alex Boznoski, this engine seeks to bring "reliability, efficiency, and exciting performance" to the Pan American line.

Among owner impressions, that reliability promise seems to hold up. On Motorcycle News, the 2021 Harley-Davidson Pan America scores an impressive 4.7/5 for owners' reviews of the engine, and a solid 4/5 for reliability and build quality. One owner praised the engine, noting its performance is "really flexible, torquey, and fast [sic] in sport mode." Others noted its performance was impressive, and that it "produces constant power throughout the rev range."

The resulting build quality provides up to 150 horsepower and 94 lb-ft of torque, which is certainly enough to blast along those "Pan American" highways with speed and responsiveness. However, the design is surprisingly lightweight, "optimized" for acceleration without the expected heftiness of such a high-capacity engine.

Tragically, the Revolution Max 1250 engine has only been implemented in a handful of Harley-Davidson models. The Pan America, 2024 Sportster S, and Nightster models have enjoyed the power of this engine, though there isn't a definitive timeline for the engine's future. 

Considering the abundance of owner reviews available online, finding the most reliable Harley engines is fairly straightforward. Building off of our list of the best overall Harley engines, we took a deep dive into the customer responses to find which specific models proved their longevity. There are two types of sources for owner reviews: forums like Reddit, V-Twin Forum, and Harley-Davidson Forums, as well as expert testing sites that compile owner reviews like Motorcycle News and Motorcycle Valley. There's also Motorcycle.com, where you can search for a specific make and model to find what owners have to say about your bike. 

Harley-Davidson itself was the primary source for horsepower and torque, as well as other features and engine specs. However, private owners provide less biased perspectives into the reliability of Harley engines, so any source of impartial feedback is exceptionally valuable.