Importance of the Correct Base Nut Tightening Procedure

It’s important to constantly stress the correct cylinder base nut tightening procedure. Operators in the field are occasionally having engine problems and malfunctioning after reinstalling cylinders, and not tightening the cylinder base nuts correctly. The latter tends to cause crankshaft bearing shifting, crankcase fretting or broken cylinder studs, and possible engine failure.

Maintenance people should ensure that torque wrenches have been correctly calibrated before accomplishing cylinder base nut tightening. After reinstalling cylinders, a ground run of the engine should be accomplished as outlined in the Lycoming “Engine Operator’s Manual,” followed by a shutdown and inspection. Then the engine should be test flown normally, and following the flight, a good inspection of the engine should be made before returning the aircraft to routine use.