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Most Common Milwaukee-Eight Engine Problems

Most Common Milwaukee-Eight Engine Problems

Harley Davidson is a popular American motorcycle brand that has been producing reliable, high-quality motorcycles since 1903. Harley Davidson keeps updating their engines to improve their performance and power output, introducing new engines every two decades. Most Harley Davidson touring and heavy-duty motorcycles have moved on from Twin-Cam engines and are now powered by Milwaukee-Eight engines. The Milwaukee-Eight engine is considered to be a more powerful and improved version of the Twin Cam engine. However, Milwaukee-Eight (M8) engines have a long history of suffering from mechanical issues, including oil leakage, power loss, engine failure, and cold-start issues. This article discusses the most common problems with Milwaukee-Eight engines.

1. Milwaukee-Eight Engine

Milwaukee-Eight Engine
Photo Credit: @cycleworld

Introduced in 2017, the Milwaukee-Eight is a heavy-duty engine that powers heavyweight Harley lineups, including the Harley Grand American Touring and Harley trikes. The Milwaukee-Eight engine comes in two sizes: the Milwaukee-Eight 107 or the Milwaukee-Eight 114.

The standard Milwaukee-Eight 107 engine has an oil-cooled system that powers many well-known Harley Glides, including the Street Glide, the Electra Glide, the Road Glide, and the Harley Road King. Liquid- and air-cooled Milwaukee-Eight 107 engines power many heavyweight touring bikes, including the Harley Road Glide Ultra, the Harley Tri Glide Ultra, and the Harley Ultra Limited. Meanwhile, the Harley CVO™ models run on a 114 cu in liquid-cooled, Milwaukee-Eight 114 engine.

The Milwaukee-Eight engines are popular among Harley Davidson fans and riders. These engines have a high-power output, ensuring smooth torque delivery and acceleration. However, many motorcycle enthusiasts have reported several issues with their Milwaukee-Eight engines.

2. Oil Sumping

One of the most frequently reported problems with the Milwaukee-Eight engine is oil sumping. If you own a 2017–2019 Harley Davidson model fitted with a Milwaukee 8 engine, you are most likely to face the oil sumping issue.

The Milwaukee-Eight engine is lubricated with oil to reduce friction and heat when the parts rub against each other. If the motorcycle is not running for a long time, the oil will go back into the tank. However, oil sumping occurs when oil accumulates in the crankcase instead of going back into the tank. Oil sumping occurs due to a faulty oil pump. If you see clouds of smoke coming out of the exhaust pipes when you start your motorcycle, this is a sign of oil sumping. Over time, the oil continues to build up in the crankcase, which causes the engine’s performance to worsen.

There are several indications your Milwaukee-Eight engine is suffering from oil sumping, including:

  • If too much oil accumulates in the crankcase, it might start to leak from the engine’s right side. Always check your motorcycle’s engine for any oil leakage after you finish a ride, especially after a long tour.
  • Having the right quantity of oil will ensure your engine and crankshaft perform correctly. However, oil sumping could cause the engine’s performance and power to deteriorate. The Milwaukee-Eight engine will not be able to produce an adequate power output and prevent acceleration.
  • If there is too much oil in your Milwaukee-Eight crankcase, it can also cause the air filter to choke due to having a large amount of carbon and debris. This can result in unbalanced air and fuel mixture and cause more fuel to burn. A clogged air filter negatively affects fuel economy and engine performance.
  • Oil sumping can cause your engine to overheat. High temperatures can cause the internal engine parts to become worn out quicker and cause the Milwaukee-Eight engine to fail.

2.1 How to Resolve the Milwaukee-Eight Engine’s Oil-Sumping Problem?

The only way to resolve the Milwaukee-Eight engine’s oil sumping problem is to install a new oil pump, which can cost between $300-$700, including labor costs. Also, if you plan to buy a Harley Davidson motorcycle powered by the Milwaukee-Eight engine, make sure to buy a 2020 or newer model.

3. Gear Oil/Transmission Fluid Problems

To ensure smooth gear shifts and transmission operation, the gears are lubricated with oil to reduce friction between parts. However, if the gear oil level drops, this could cause the gearbox and the engine to become damaged. The lack of gear oil will be even worse on the gearbox and engine while riding at high speeds.

There are several indications your Milwaukee-Eight engine is suffering from gear oil issues including:

  • If your Milwaukee 8 engine has low gear oil or transmission fluid levels, it becomes difficult to shift between gears, putting more pressure on the transmission and engine.
  • If the gear oil level is low, this will result in more friction between the metallic parts, causing them to grind against each other and produce an unpleasant noise.
  • The metallic parts constantly grind against each other due to a lack of gear oil level causing an increase in friction and heat. Not refilling the gear oil will result in the engine suffering permanent damage.

3.1 How to Resolve the Milwaukee-Eight Engine’s Gear Oil Problem?

This issue can be resolved by regularly checking the gear oil level and following a strict maintenance schedule. If you see any indication of low gear oil level, get your motorcycle checked by a professional mechanic to find the oil leak and replace the damaged parts.

4. Cold-Start Problems

While the cold-start issue is not as severe as the oil sumping and low gear oil level, it can be frustrating if the Milwaukee-Eight engine refuses to start in cold temperatures below 10°C. Checking the battery is the first thing you should do to determine why the motorcycle is not starting in the cold. If the battery is fine, the issue may be because of the engine oil.

4.1 How to Resolve the Milwaukee-Eight Engine’s Cold-Start Problems?

Check if the battery is working correctly or not. If the battery provides nominal voltage, then the cold start issue may be due to the engine oil. Using engine oil that is incompatible with your motorcycle’s engine or too viscous can result in cold-start problems. You should check the motorcycle owner’s manual or consult a mechanic if you are unsure what type of engine oil to use.

5. Fuel Injection and Lean Mixture Problems

Lean mixture occurs when there is more air in the fuel-air mixture during combustion. This problem can be due to a faulty fuel injection system delivering less fuel to the engine.

The Milwaukee-Eight’s fuel injection and lean mixture problems can cause erratic throttle response, poor idle power, loss in power output, slow acceleration, and low-range power.

5.1 How to Resolve the Milwaukee-Eight Engine’s Fuel Injection and Lean Mixture Problems?

The Milwaukee-Eight engine’s fuel injection and lean mixture problems can be modified with a BoosterPlug upgrade to ensure a proper mixture of air and fuel. The BoosterPlug is easy to install and ensures better engine life, combustion, and fuel economy. After installing this upgrade, you will notice a significant difference in power output, acceleration, throttle response, and fuel efficiency.

6. Pros and Cons of Milwaukee-Eight Engines

Milwaukee 8 Engines Pros
Milwaukee 8 Engines Cons
Better overall performance
Oil sumping
Smooth riding experience
Oil leakage
Four valves per cylinder
Produces more horsepower and torque
Cold-start problems
good acceleration
Produces vibrations
Less noise
Produces irritating noises
Less heat
Faulty fuel pump design
Single cam design
Faulty oil filters
Soul-satisfying exhaust note
Can only be installed on a limited number of models
Comes with an assist & slipper clutch
Gear oil issues
Engine stalling
Single internal counterbalancer
Improper air and fuel mixture
Reduced vibrations
Clogged air filter
Better fuel economy
Carbon deposits and engine sludge
More exhaust and intake flow
Engine produces clouds of smoke
Meet Euro 4 emissions
Engine misfires

7. Takeaway

The Milwaukee-Eight engine is a powerful and torquey engine that powers Harley touring bikes and CVO™ models. It has a good reputation among motorcycle enthusiasts, particularly Harley Davidson fans. However, the early version of this engine suffered several problems, including oil sumping, power loss, gear oil problems, cold-starting issues, and a lean mixture that were difficult to fix for several years in its production. If your Milwaukee-Eight engine is suffering from such problems, you can try any of the solutions covered in this article. If the problem persists, you should immediately get the motorcycle checked by a mechanic to avoid engine failure.

A well-maintained engine and motorcycle lasts longer, performs better, and requires a lot of care, time, and money to ensure it lasts you a couple of years. Viking Bags offer several aftermarket parts that improve your motorcycle’s aesthetic appeal and safety. The luggage options available at Viking Bags include saddlebags and sissy bar bags. Other aftermarket parts include sissy bars, crash bars, fairings, and handlebars.

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