In The Shop: M8 Oil Sumping Issue

M8 OIL SUMPING ISSUE

There is a common M8 oil sumping issue with some early Milwaukee Eight motors. If you own a 2017 to 2019 Harley Davidson with a Milwaukee Eight motor and have had excessive oil blow-back from the vicinity of your air intake, you may be experiencing this M8 oil sumping condition.

The M8 oil sumping occurs when motor oil builds up in the crankcase. The reason for this occurrence in the Milwaukee Eight motor is, in our opinion, from an incorrectly engineered oil pump. 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 flywheels rotate through the excessive oil and turn the oil into an aerated state. 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.

M8 oil sumping can end up resulting in excessive friction and power loss on a Milwaukee Eight motor. The build up of crankcase oil can actually be turned into a froth of air and oil from the constant rotation of the flywheels. When the oil is aerated this way, it makes oil pump scavenging more difficult. This does not only restrict oil return to the oil pan. Oil is also restricted to the motor’s top end. Overall, there is a chain reaction that often results in an excess of oil being forced out through the head breather bolts. The condition can also cause oil leaks, lifter noise, and even possible premature wear and engine failure.

We should note that this M8 oil sumping condition is more likely to develop during longer rides at constant highway speeds.

The only way to eliminate this problem is by changing oil pumps. 2020 Harley Davidson oil pumps have been re-engineered to remedy this sumping issue. Being that Harley has not issued a recall, the expense of this repair falls on the owner. We highly suggest upgrading to an S&S M8 oil pump. We feel that S&S offers the highest quality Harley Davidson motor parts on the market. Also, 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 and not by the loyal customer.

At the time of shooting our M8 Cam Upgrade series HD just that week released a new oil pump and S&S had it’s coming out the following week. We used the newest HD Oil Pump and things have been working well.