since 1940

Fluctuating oil pressure in Lycoming or Continental aircraft engine

Do not fly airplane with fluctuating oil pressure. Fluctuating oil pressure can  occur because of bearing failure and immediately proceed complete engine failure. 

Other causes of fluctuating oil pressure include:

Fluctuating oil pressure seen as rapid needle movement is the result of the pump gulping air. Air is compressible and drives the needle crazy. This leak may come from the pump body where a little nick in the surface prevents the body from lying flat.

Lycoming engines have two ways of picking up oil: via the pickup tube, or through the casting. Those engines that use a pickup tube may suck air through the inlet gasket on the pickup tube. Engines that pickup oil through the casting may suck air through the sump gasket.

Lycoming Engines: Incorrect oil pressure housing. This will usually cause problems after the oil warms up.

 

Lack of oil in Lycoming engine  damages the connecting rod bearing The rod journal rides on an oil film (called hydrodynamic lubrication) and does not touch the bearing during operation. Without adequate oil flow to the bearing, the oil film is ruptured and contact is made between the journal and the bearing.  Notice the evidence of high heat on the connecting rod and the piece of bearing back sticking out the right hand side of the rod.

Frictional forces melt the bearing Babbitt until the bearing shell starts to extrude out the side of the connecting rod (shown on the right). Excessive clearance causes the rod bolts to pound and they eventually fail in fatigue. Notice also the heat damage to the rod bolts. Pilot Description of Symptoms The pilot assumed that the loss of power  might be caused by an ignition problem, so he made an emergency landing. With the engine still running, he tried to take off but aborted due to not enough power.                 When the maintenance shop checked the engine they  found  no oil in the sump. The connecting rods were burnt, the bearing destroyed (including the crankshaft's journals), and one bearing was extruded between the connecting rod and the crankshaft cheek.

Lycoming connecting rod caps. This is what happens if you loose oil pressure to the connecting rods. It doesn't matter what additive "treatment or claims" about running without oil. Once you loose the OIL FILM you melt the bearing material off of the shell. This makes the bearing loose on the connecting rod journal. The pounding of the loose rod soon fatigue fails the connecting rod bolts.

It is possible to shut down the engine before the rod breaks off but after the bearing material has melted off the rod. If you add oil to the engine, check the oil screen for metal (useless in this case since without oil circulation none of the metal circulates to the oil screen), and then take-off you get an in-flight engine failure when the pounding rod breaks the bolts. If your engine suffers loss of oil pressure you must remove the connecting rods to inspect the bearings.

A drop off of idle oil pressure or momentary loss of propeller control can be caused by a bearing starting to go.

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