Service Instruction No. 1191 A

Cylinder Compression

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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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