Fill A Flathead Oil Filter

Flathead engines are powerful.

Filling the oil filter on your motorcycle’s Flathead engine helps keep the filter from leaking and ensures proper engine function. The oil filter needs to be changed every time that the engine oil is changed. The oil filter will be in a different place on different Flatheads, but is always mounted to the oil pump, which will be connected to the crankcase. You can complete this job at your home in about two minutes.


1. Place the oil filter wrench around the oil filter and turn the filter counterclockwise. Once the filter comes lose, remove it from the oil pump.

2. Pour fresh motor oil into the new oil filter slowly. Fill the new oil filter halfway and tilt the filter side to side a few times to settle the oil.

3. Fill the new oil filter all the way with fresh motor oil. You will see the motor oil at the top of the filter once it is full. Rub motor oil around the rubber seal that is around the upper edge of the filter. Place the filter onto the oil pump and turn it clockwise until snug.