Service Instruction No. 1191 A

Cylinder Compression


Supersedes Service Instruction No. 1191

September 28, 1998


All Lycoming aircraft engines.


As required to determine cylinder compression

The condition of the working parts in the combustion chamber of a cylinder can be determined by measuring the static leak rate of the cylinder as compared to the leak rate through an orifice of specified size. This is accomplished by attaching a differential compression measuring device, which incorporates the orifice, to one spark plug hole of the cylinder while the piston is at top center of the compression stroke.

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