Sealing screws holding OMC gearbox shells together

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  • olcah
    olcah

    US Member - 1 Year
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    #192152

    I notice OMC tech manual/bulletin on sealing 1950s gearboxes says to use Sealer 1000 (3M 847 nowadays) on the sealing surfaces/spaghetti and to also use Sealer 1000 on the screws holding the lower gearbox shell to the upper.
    In the past I have sealed those screws with OMC 508235 gasket sealer. That is more convenient as one is in a hurry to get the gearbox halves together before the sealer 1000 dries. If the screws are sealed with the OMC gasket seal the threads can be coated in advance as that sealer is very slow drying.

    Just curious what others might think about this?
    Thank you.

    frankr
    frankr

    US Member - 1 Year
    Replies: 4660
    Topics: 45
    #192155

    I just grabbed a service manual at random and it says to apply OMC Gasket Sealer to the screws, so you are doing right by the book. Truth is, I don’t think the screws need any sealer. Sock them in tight with your hand impact screwdriver and they won’t leak. The threads are within the oil chamber, so water corrosion is not an issue. But go ahead and do as you are and feel good.

    bobw
    bobw

    US Member - 1 Year
    Replies: 756
    Topics: 31
    #192160

    I’ve always done as you described and used OMC gasket sealer on the screws. And as you noted, I coat the screws in advance so they are ready to go as soon as the gearcase pieces are put together.

    Bob

    1954 Johnson CD-11
    1956 Johnson RD-18
    1958 Johnson QD-19
    1959 Johnson QD-20

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    crosbyman

    Canada Member - 1 Year
    Replies: 1389
    Topics: 180
    #192166

    I apply a few layers of yellow teflon tape to fill up the threads and a dab of gasket sealant

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    billw

    US Member - 2 Years
    Replies: 1079
    Topics: 38
    #192182

    I use brush on gasket sealer for the screws. I have had to torch out a few, in my life here in the salt.

    Long live American manufacturing!

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    Tinman

    US Member - 1 Year
    Replies: 212
    Topics: 37
    #192190

    I just use the 847. Messy but it works. So far no problems.

    labrador-guy
    labrador-guy

    US Member - 2 Years
    Replies: 254
    Topics: 29
    #192193

    Frank is right the treads don’t need sealer but, the heads of the bolts do. Sometimes over the years the screws get switched out and the fasteners don’t have the flange on the head of the screws. It doesn’t take much, if you slap some dope on the treads some will also get on the flange. JMHO

    dale

    olcah
    olcah

    US Member - 1 Year
    Replies: 360
    Topics: 77
    #192198

    This will go into my notebook. Thank you everyone.

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    fleetwin

    US Member - 2 Years
    Replies: 2833
    Topics: 36
    #192206

    OK, well not to over analyze things, but this area has to be properly sealed because it is in the oil cavity and can cause an oil leak. There are two separate issues here when it comes to using sealer on the skeg screws. Like Frank says, the threads of the screws are behind the spaghetti seal, so really don’t really need sealer to prevent corrosion. But, the mating surface between the shoulder of the screw and its mating surface on the skeg must seal properly. Again, this area is inside the spaghetti seal, so imperfections will create an oil leak.
    Like Frank says, the metal to metal compression fit usually seals itself without the need for sealer. But, we are talking about parts that are very old, may have been disassembled several times before, and have been exposed to salt water. So, it is very important to look at the screw holes in the skeg that mate to the screw shoulders, along with the screw shoulders themselves. . Obvious problems in this area will cause sealing problems…And, there is nothing worse that getting a unit all resealed and assembled, only to find a leakage issue when pressure testing, we have all been through this before. So, the important area for sealer is under the screw shoulders, and the typeM/847 sealer will be more effective . I have often wondered why OMC never put orings under the screw heads, but the answer seems obvious, cost. Because, like Frank says, the metal on metal compression fit seals itself up 99 percent of the time.
    And even though the screw threads are somewhat protected from corrosion by the gear lube, I always use the sealer on the threads also. Admittedly, I’m usually overkill when it comes to lubing/sealing stuff up for salt water use. I have seen a few screws corroded in place over the years also, but this is usually on units that leaked and were full of water.

    frankr
    frankr

    US Member - 1 Year
    Replies: 4660
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    #192210

    Well said.

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