Reply To: Johnson 15hp

[Don]

Well, I don’t think I would use the 847 sealer on the gaskets only because it sets up too fast.  It would be hard to coat both sides of the gaskets and get them installed before the 847 sets up.  847 is great sealer, but is messy and sets up very quickly.  Again, you can surely use the 847 sealer, but you have to install the gaskets very quickly to avoid premature sealer set up.    Sure, gasket sealer isn’t required on new engines/parts, but only because those surfaces are clean and flat.  Not fair to make this assumption about a 50yr old outboard, I would use the brush on liquid gasket sealer from OMC/Merc/Yamaha.  Much easier to work with and less messy.  Please do NOT use silicone goop or anything like that.  Needless to say, even the best gasket sealer can not overcome major surface imperfections/gouges/erosion, so inspect everything carefully and make sure to clean out all the threads to make sure the screws thread in without jamming.  The last thing you want is for block threads to strip out during installation.

And yes, I realize that many of the OMC head gaskets have “no sealer” stamped on them.  These gaskets have a bit of gasket sealer impregnated in them that releases with heat.  There is no harm in using a bit of gasket sealer as well though, your decision.  Gasket sealer surely has little/no sealing effect on the inner cylinder sealing surface where the metal sealing ring is.  A sealing issue in this area has to be corrected, gasket sealer will be blown out quickly.  The gasket sealer used on the outer edges will help ensure there are no minor external water leaks though.