Sunday, 01 October, 2023

Harley M8 Oil Pump Issue Explained


There is a Harley M8 Oil Pump Issue plaguing the 2017-2019 Harley-Davidson motorcycles equipped with the Milwaukee Eight engine. You should definitely be aware of this so you know if your bike is affected.

If you own a Harley Davidson with a Milwaukee Eight motor built before 5/22/19 and have had excessive oil blow-back from the vicinity of your air intake, you may be experiencing this issue.

What is the Harley M8 Oil Pump Issue?

The specific issue is known as “Oil Sumping”. Oil sumping occurs when excess engine oil builds up in the crankcase. The reason for this on the Harley M8, in my opinion (and many others’) is due to a flaw in the oil pump design. Sumping begins when the suction side of the oil pump does not scavenge enough oil from the crankcase. As oil begins building up in the crankcase, the oil level in the sump increases. Eventually, the flywheels rotate through and aerate the oil.

When the oil is aerated this way, it makes oil pump scavenging more difficult. At this point, oil becomes increasingly trapped in the bottom end. It can cease to return through the oil pump and to the oil pan. This creates a chain reaction of issues. Reduced oil flow to the top end, increased top end noise, and an excess of oil being forced out of the breather bolts. The condition can also cause oil leaks, lifter noise, and even possible premature wear and engine failure.

When Does the Oil Sumping Issue Occur?

M8 oil sumping is more likely to present itself during longer rides and/or higher RPM. If you ride short distances, or mostly on city streets & side roads, you may not notice the Harley M8 Oil Pump Issue. After a shorter ride, the bike will build up some oil in the crankcase and then you’ll shut the bike down. On the next startup and idle, the crankcase will empty, and the process starts over again.

The Milwaukee-Eight oil sumping issue happens over time. So, if you ride harder on those twisties or long distances at highway speeds, the issue is more likely to reveal itself.

The Fix

Unfortunately, installing a new Harley M8 Oil Pump is the only real fix. Harley began using an updated oil pump in bikes built after 5/22/19 to correct the issue. Being that Harley has not issued a recall, the expense of this repair falls on the owner.

Harley M8 Oil Pump Issue

Fueling, and S&S all offer an upgraded oil pump which will solve the sumping issue. We don’t recommend buying HD’s updated oil pump. It wouldn’t make much sense to give Harley-Davidson more of your $$ for an issue that should be addressed, remedied, and covered by the factory.

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