Milwaukee 8 Problems – How Good Is This Harley Engine?

Harley-Davidson is a company that can only be seen as a mogul among motorcycle manufacturers. Founded in 1903 in Milwaukee, Wisconsin, it has lived through the impossible to become the renowned brand that it is today.

One of its biggest successes was the introduction of the Milwaukee 8 engine, which provided numerous quality-of-life improvements for avid bikers across the world. But is this engine truly as great as they claim or is it just a hype designed to ensnare potential buyers? Let's find out the truth together.

In this article, you'll learn:

• The strong points of the Milwaukee 8 engine
• The 3 most common issues with the Milwaukee 8 engine
• Whether you should buy a bike with the Milwaukee 8 engine or not

What makes Milwaukee 8 so good?

Following an exhaustive survey, the Harley Davidson company decided to step up its engine game. Their rigorous development led to the birth of the Milwaukee 8 engine. Unlike the engines that came before it, this new mode features 8 valves split evenly between two cylinders. Hence the name.

The greater number of valves makes this engine much more efficient in terms of fuel. The improved airflow maximizes the amount of gas used to power your bike. At the same time, it makes Milwaukee 8 pack a much bigger punch than its predecessors. This allows you to reach higher revs much faster.

But the M8 engine's virtues don't end with just the stellar performance. On the contrary, the state-of-the-art technology makes Milwaukee 8 much quieter than the previous models. Moreover, it doesn't produce nearly as much vibration, which makes for a much smoother ride. If this isn't perfection, then what is?

However, while we humans might chase after perfect, we will never reach it. Despite the groundbreaking progress this engine represented, it does have its flaws. The real question is, are they grave enough to discourage you from buying this bike?

That's what we'll discuss in the next section.

What are the common Milwaukee 8 problems?

No matter the brand, every motorcycle has its shortcomings. When choosing the right bike, you should look for one with the fewest known problems. Of course, the severity of the existing problem is also an important factor.

1) Oil sumping

This is arguably one of the most common problems with the M8 Engine. Read carefully especially if you own an M8 bike manufactured from 2017 to 2019. Newer models have resolved the issue. The bad news is that if you own one of the older models, then you'll have to pay for the repairs yourself. Since Harley-Davidson did not issue a recall, they won't cover these expenses.

But what exactly is oil sumping? Most engines rely on oil to reduce heat and friction that result from the constant combustion cycles. When you don't use your bike, the oil normally falls back into the tank. However, there seem to be some inherent issues with the M8 oil pans manufactured between 2017 and 2019. Because of the poor suction, the oil remains in the crankcase. Over time, it builds up to such amounts that hinder the engine's performance.

Note that this is particularly noticeable during longer, faster rides. During short ones, the issue might not exhibit any symptoms whatsoever.

But what exactly are the symptoms of oil sumping? Here are 5 most common ones:

• Oil leaks: During longer rides, the oil might build up to such a large amount that it starts leaking. It typically leaks from the right side of your bike.
• Clogged air-intake filter: Excessive oil might block your air-intake filter.
• Poor performance and power loss: The oil is meant to reduce heat and friction. However, too much of it will drown your crankshaft. If you've ever been inside a swimming pool, then you'll know that walking through water is much more difficult than walking on land. The same thing happens here. The oil will hinder the crankshaft's movement, so it won't produce as much power as it should. Thus, you'll have issues with acceleration.
• Overheating: The excess oil may cause your bike to become uncomfortably hot. Not only is this a nuisance to you as a bike rider, but it may wear down your Halvey before its time.
• Engine Failure: In the worst-case scenario, your engine will shut down.

Now that you know what to look for, let's take a closer look at the possible solutions.  Well, there's just one - you'll need to change the oil pump. Since Harley-Davidson didn't issue a recall, you must buy the upgrade yourself. Sadly, these newer pumps can cost from $300 to $700 and that's minus the labor costs. If you're just looking for a Harley bike, stay away from the models made between 2017 and 2019.

Most sellers will tell you they recommend upgrading the pump, but they won't tell you that you absolutely have to do that. Avoid falling into their marketing machinations and buy only models made in 2020 and newer.

2) Cold starting problems

Compared to oil sumping, this is a relatively mild issue. When you attempt to start your bike at temperatures below 50 Fahrenheit, your M8 engine just won't respond.

This problem has been linked to two possible causes.

The first one is a large number of electronics present on the bike. In cold weather, they will drain your battery much faster. It just can't keep up with the high demand. Of course, this cause has nothing to do with the engine itself.

However, if your battery's just fine, then the issue likely lies in the engine oil. You might be using a type that's too viscous. Consult your manufacturer's manual to see what kind of oil you should use at different temperatures and change it if needed.

3) Transmission fluid issues

This problem is similar to oil sumping. Owners of M8 bikes have reported that their transmission fluid levels keep dropping. This is because fluid travels from the transmission into the primary. It appears to be an inherent design flaw and it worsens at higher RPM. Transmission fluid protects metallic components from damage. Once the levels drop too much, you risk engine damage.

Here are several symptoms that point to this design oversight:

• Low fluid level: The most obvious way to tell whether you don't have enough fluid is to just check its level. However, most people don't pay much attention to such trifling matters unless they have a big maintenance appointment coming up. That's why they notice this problem only once the real symptoms start appearing.
• Loud noises: Because there's not enough fluid in the transmission itself, the metallic components will grind against each other with nothing to reduce the friction. Not only does this produce a lot of unpleasant noise but it also damages your transmission.
• Overheating: As mentioned before, the constant grinding produces a large amount of heat. It may lead to damage if the issue persists.
• Difficulty with shifting gears: Naturally, low fluid levels will lead to difficulties when you shift the gears.

Just like with oil sumping, you'll need to replace the faulty part to fix this issue. In this case, you'll need to buy a primary vent. The vent itself is relatively cheap, just about $50. However, labor costs might turn out to be quite expensive.

Final Verdict

Before we pass our final judgment, let's look quickly summarize the virtues and vices of the Milwaukee 8 engine.

On one hand, this engine is smoother, stronger, and more efficient than its predecessor. No more noise and vibrations to pollute your joyride experience. The great fuel economy means fewer bucks spent on gas. Who doesn't like to hear that? The extra horsepower is just a nice finishing touch.

While we can expect every bike to have some inherent flaws, there shouldn't be any major ones. Unfortunately, that's not the case with the M8 models. The faulty oil pump allows oil to build up in the crankcase which hurts the engine itself.  While its cylinder valves might be the best ones out there, all its virtues come undone because of the oil problem. The only silver lining to this problem is that it only affects models made between 2017 and 2019. Still, it's a huge blunder for such a renowned company.

As for the cold starting issue, it's little more than a nuisance. You can simply use less viscous oils during the winter and you're all set. Overall, it's not a major problem.

However, we're not as lenient when it comes to the transmission fluid migration problem.  After all, performance is the number one factor all bikers consider when investing in a new bike. This issue reflects poorly on the performance and might discourage some potential buyers even though it's not that expensive to resolve.

So ultimately, we'd say the Milwaukee 8 engine is a true force of nature. Just make sure you stay away from the models that were manufactured before 2020 - those are the ones with the major issues. Without these issues, you're bound to fall in love with this remarkable engine.