The Milwaukee-Eight engine, introduced by Harley-Davidson in 2016, was heralded as a significant leap forward in motorcycle engineering. Boasting increased displacement, improved cooling, and more power, it aimed to address some long-standing criticisms of previous Harley engines. However, like any complex piece of machinery, the Milwaukee-Eight isn't without its share of problems. Understanding these issues can help you make informed decisions about maintenance, modifications, and even purchasing a motorcycle equipped with this engine.

Is the Milwaukee-Eight Really All That? A Look at Potential Issues

While the Milwaukee-Eight is generally a reliable engine, several common issues have surfaced since its introduction. Knowing about these potential problems can help you spot them early and take preventative measures. Let's dive into some of the most frequently reported concerns.

Oil Transfer: The Case of the Mysterious Oil Migration

One of the most talked-about issues with early Milwaukee-Eight engines is oil transfer. This occurs when oil migrates from the oil tank into the crankcase. The problem is primarily found on the 2017-2019 models, but can affect some others as well.

How Does This Happen?

The root cause is usually traced back to the check valve in the oil pump. This valve is supposed to prevent oil from flowing back into the crankcase when the engine is off. If the check valve fails, oil can seep past it and accumulate in the crankcase over time.

What are the Symptoms?

  • High Oil Level: You might notice that your oil level is significantly higher than it should be.
  • Oil in the Airbox: Excess oil in the crankcase can be forced into the airbox through the breather system.
  • Engine Knocking/Pinging: In severe cases, the excessive oil in the crankcase can lead to engine knocking or pinging.
  • Wet Sumping: This is when a large amount of oil accumulates in the crankcase, potentially causing issues with oil pressure and lubrication.

What Can You Do About It?

  • Regular Oil Level Checks: Keep a close eye on your oil level, especially after the bike has been sitting for a while.
  • Check for Oil in the Airbox: Inspect your airbox regularly for signs of oil accumulation.
  • Consider a Check Valve Upgrade: Many aftermarket companies offer upgraded check valves that are more reliable than the original. Some owners opt for a complete oil pump replacement.
  • Short Trip Riding: Oil transfer is made worse with short trip riding as the engine does not get hot enough to burn off any oil that has entered the combustion chamber.

Overheating: Feeling the Heat on Your Harley

While all air-cooled engines generate heat, some Milwaukee-Eight engines, particularly the larger displacement versions (114, 117, and 131 cubic inches), have been reported to run hotter than some riders find comfortable.

Why is it Hotter?

  • Increased Displacement: Larger engines naturally produce more heat.
  • Tighter Emissions Regulations: Leaner fuel mixtures, implemented to meet emissions standards, can contribute to higher engine temperatures.
  • Rider Position: The position of the rider and the exhaust system can contribute to the heat felt by the rider.

What are the Symptoms?

  • Excessive Heat Radiating from the Engine: You might feel a significant amount of heat coming from the engine, especially around your legs.
  • Reduced Engine Performance: In extreme cases, overheating can lead to reduced engine performance and potential damage.
  • "Parade Mode" Stalling: Prolonged idling in hot weather can cause the engine to stall.

What Can You Do About It?

  • Consider an Oil Cooler: Installing an oil cooler can help to dissipate heat and keep the engine running cooler.
  • Install a Fan-Assisted Oil Cooler: Installing an oil cooler with a fan can provide additional cooling during stop-and-go traffic.
  • Adjust Fuel Mixture: A professional tuner can adjust the fuel mixture to run slightly richer, which can help to lower engine temperatures. Note: This may affect emissions compliance.
  • Exhaust Upgrades: Aftermarket exhaust systems can improve exhaust flow and reduce heat buildup.
  • Rider Heat Deflectors: These deflectors redirect heat away from the rider's legs.
  • Upgrade to a Liquid-Cooled Model: Harley-Davidson offers liquid-cooled versions of the Milwaukee-Eight engine, which provide superior cooling performance.

Cam Chain Tensioner Issues: A Familiar Problem Returns

While the Milwaukee-Eight uses a different cam drive system than the older Twin Cam engine, some owners have reported issues with the cam chain tensioners.

What's the Concern?

The hydraulic cam chain tensioners, though improved, can still experience wear and tear over time. In some cases, the plastic shoes on the tensioners can degrade, leading to reduced tension and potential engine damage.

What are the Symptoms?

  • Rattling Noise from the Engine: A rattling noise, especially at idle or low RPMs, can be a sign of worn cam chain tensioners.
  • Loss of Engine Performance: Worn tensioners can affect valve timing and lead to a loss of engine performance.
  • Metal Debris in the Oil: In severe cases, worn tensioners can shed metal debris into the oil.

What Can You Do About It?

  • Regular Inspections: Have your cam chain tensioners inspected periodically, especially if you notice any unusual noises or performance issues.
  • Consider Upgraded Tensioners: Many aftermarket companies offer upgraded cam chain tensioners with more durable materials. Some of these systems replace the tensioners entirely with gear-drive systems.
  • Follow Recommended Maintenance Intervals: Adhere to Harley-Davidson's recommended maintenance intervals for oil changes and other services.

Valve Train Noise: The Milwaukee-Eight Tick

Some Milwaukee-Eight engines are known to exhibit a noticeable valve train noise, often described as a "tick" or "sewing machine" sound.

Why is it Happening?

This noise is generally considered normal for the Milwaukee-Eight engine and is often attributed to the design of the valve train and the hydraulic lifters. However, excessive noise can be a sign of a problem.

What are the Symptoms?

  • Ticking or Sewing Machine Sound: A noticeable ticking or sewing machine sound coming from the engine, especially at idle.

What Can You Do About It?

  • Ensure Proper Oil Level: Maintaining the correct oil level is crucial for proper lubrication and can help to minimize valve train noise.
  • Use High-Quality Oil: Using a high-quality oil that meets Harley-Davidson's specifications can also help to reduce noise.
  • Check Valve Lash: In some cases, excessive valve lash can contribute to valve train noise. Have a qualified mechanic check and adjust the valve lash if necessary.
  • Consider Adjustable Pushrods: Aftermarket adjustable pushrods can allow for more precise valve train adjustment.

Compensator Issues: The Dampening Dilemma

The compensator is a crucial component in the primary drive system, responsible for dampening vibrations and reducing stress on the drivetrain. Some Milwaukee-Eight engines have experienced issues with the compensator.

What's the Problem?

The compensator can wear out over time, leading to excessive noise and vibration. In some cases, the compensator can even fail completely.

What are the Symptoms?

  • Loud Clunking Noise: A loud clunking noise, especially when starting or shifting gears, can be a sign of a worn compensator.
  • Excessive Vibration: Increased vibration, especially at lower RPMs, can also indicate a problem with the compensator.
  • Difficulty Shifting Gears: A worn compensator can make it difficult to shift gears smoothly.

What Can You Do About It?

  • Regular Inspections: Have your compensator inspected periodically for signs of wear.
  • Consider an Upgraded Compensator: Many aftermarket companies offer upgraded compensators with more durable components.
  • Proper Lubrication: Ensure that the compensator is properly lubricated according to Harley-Davidson's recommendations.

Frequently Asked Questions (FAQ)

Q: Is the Milwaukee-Eight engine reliable?
A: Generally, yes. While it has some known issues, the Milwaukee-Eight is considered a reliable engine when properly maintained.

Q: What years are affected by oil transfer?
A: The primary years affected by oil transfer are 2017-2019, but some other years may also experience this issue.

Q: How can I tell if my engine is overheating?
A: You'll likely feel excessive heat radiating from the engine, especially around your legs, and may experience reduced engine performance.

Q: What's the best oil for a Milwaukee-Eight engine?
A: Use a high-quality oil that meets Harley-Davidson's specifications for your engine.

Q: Are aftermarket parts worth it for the Milwaukee-Eight?
A: Aftermarket parts, like oil coolers and upgraded tensioners, can address some of the engine's known issues and improve performance.

The Milwaukee-Eight: A Powerful Engine with Potential Pitfalls

The Milwaukee-Eight engine offers significant improvements over its predecessors, but it's essential to be aware of potential problems. By understanding these issues and taking preventative measures, you can ensure that your Milwaukee-Eight engine provides years of reliable performance. Regular maintenance and attentive observation are key to keeping your Harley running smoothly.