Customers often call regarding problems they are having pre-oiling Continental engines. While it is important to follow the OEM instructions while pre-oiling your engine (Continental provides instructions for engine pre-oiling in section 5-2.9 of Maintenance Manual M-0). Aero Recip would like to provide you with a few tips which can ease the process and help to ensure success. While Continental recommends using a pressure vessel to pre-oil, it can still be difficult to get an oil pump to prime and build pressure during cranking or at engine start-up. Unless there is oil in the body of the oil pump to create suction, it is impossible for the pump to draw oil from the sump. When an overhauled engine is installed on an airplane, it will have been shipped from Aero Recip with the oil drained. Prolonged storage without oil can allow the oil that remains in the oil pump after test run to drain away. This often results in difficulty getting the pump to prime during preoil. As part of your pre-oil process, and prior to cranking the engine, it can be beneficial to introduce oil into the oil pump housing either through the oil filter head, or screen housing.
The following are photos of typical Continental six cylinder oil pump housings.
Aero Recip technicians use a plastic bottle with a squirt nozzle to add engine oil to the gear housing portion of the oil pump body. It is important to note that oil needs to flow into the areas indicated. It can be helpful to pour in a quantity of oil, rotate the engine backward (if possible) and then add more oil. Spin on a partially filled oil filter or install the oil screen and crank the engine with top spark plugs removed. The oil pump should now draw oil from the sump and oil pressure will build within the engine.
Continental engines incorporate several configurations of oil pump screen/filter housings. The photos here depict a common type of oil pump housing which would be found on 470, 520 & 550 engines found in many Cessna aircraft. With other types of oil pump bodies, it may require some ingenuity to get oil into the gears, it can be helpful to use a small hose in conjunction with the squirt bottle.