Safety Tip - Sealant Use

The latest revision of Lycoming Service Instruction No. 1125 specifies POB No. 4 Perfect Seal and silk thread as the generally used items for sealing crankcase finished parting surfaces that do not employ gaskets. Two other products, RTV-102 or LOCTITE-515 applied as a very thin film without silk thread, may be used as alternate materials for sealing crankcase parting surfaces.

Other sealants have not been tested and approved for this purpose, and NONE are approved for other uses in the assembly of Lycoming engines.

Improper use of these and other sealing compounds can create serious problems. As an example, a red-colored sealant was used by a mechanic to hold the pressure-screen gasket in place. As the material solidified, pieces broke loose and eventually blocked the engine’s small oil passages causing oil starvation and engine failure. The bottom line: Only use those sealant materials approved by the Lycoming Overhaul Manual and other service publications, and only use them for approved purposes.