Service Instruction No. 1125 D

Alternate Crankcase Parting Surface Sealants

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Supersedes Service Instruction No. 1125C

October 17, 2008


All Lycoming opposed cylinder engines.


During engine assembly.

The use of POB No. 4 Perfect Seal sealant (POB) and silk thread has been used generally for sealing finished parting surfaces that do not employ gaskets. This practice has always been satisfactory when correctly applied. However, we have tested and approved General Electric Company’s RTV-102 and LOCTITE-515 as alternate sealants which may be used at field service overhaul facilities where trouble may have been experienced in applying POB and silk thread.

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