Service Instruction No. 1485 A

Exhaust Valve and Guide Identification Procedure

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Supersedes Service Instruction No. 1485

July 2, 2003


All Lycoming reciprocating aircraft engines unless installed in a rotary-wing aircraft.


Half way to recommended TBO or at 1000 hours of operation, whichever occurs first or earlier at owner’s discretion or anytime valve sticking is suspected.

As a product improvement, Lycoming has introduced a new exhaust valve guide material with an increased chrome content for improved wear characteristics. The incorporation of this guide material has significantly reduced the amount of valve guide wear (bell-mouthing) seen by some operators of Lycoming engines.

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