1941 Mercury KB-3 Top Crank Oil Seal?

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  • Buccaneer

    US Member - 1 Year
    Replies: 6452
    Topics: 958
    #271554

    When I put the powerhead of the subject motor back together today,
    there sure looks like there’s room for a top crank oil seal.
    I never removed any, or else if “fell out” by itself and rolled away.

    I found a master parts list of sorts, for “K” model Mercs.
    It shows them all having a seal, and all the same part number.

    A 26-21642 < (79831)
    or
    Sierra 18-2055, with specs of .750 shaft, 1.127 OD, .149 thickness

    I dug through my seal supply, and found a CR seal that I measured with an OD
    of 1.1285, which one would think would work, but when I measure the
    bore of the crankcase where the seal would go, it seems to be “out of round”
    and varies between 1.115 to 1.120 diameter.

    That seems like way too tight of a fit, and of course the crankshaft is installed now,
    otherwise, machining on the OD would have been easier.

    Just wondering, did all these “K” models in 1941 have top crank seals?
    Or may I be trying to fix something that aint broke?

    DSCN5879

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    The Boat House


    Replies: 4074
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    #271579



    A while a go I went through a 1941 Neptune horizontal twin that had a
    cork upper crankshaft seal. Possibly that is what was used on your Merc?
    Tubs


    Buccaneer

    US Member - 1 Year
    Replies: 6452
    Topics: 958
    #271582

    According to the part book for “K” models, they were a neopreme seal.
    I went ahead and installed the CR seal I had on hand.
    I found that the seal bore was “out of round” because the thin
    bore shoulder was dented in slightly in a part lifetime.
    I did a little hand work with my “de-burrer” and finally
    got the seal in.

    Prepare to be boarded!


    green-thumbs

    US Member - 2 Years
    Replies: 550
    Topics: 41
    #271584

    Industry standard seal part # 7415 is a physical fit for upper crankshaft seal on Early K Models. For this application there is no need to upgrade to special features which will multiply the cost without improving performance or service life.

    Louis

     

    Per seal catalog 7415 is for .750″ shaft,  1,124 O.D,  & .156 thick tMercury part number cross references to 7415

    • This reply was modified 1 week, 1 day ago by green-thumbs.

    Buccaneer

    US Member - 1 Year
    Replies: 6452
    Topics: 958
    #271601

    Louis, I had a CR seal CR 7414 on hand, and that’s what I ended up using.
    It seem to be a perfect fit once I got the crankcase bore doctored up a little.

    DSCN5880

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    green-thumbs

    US Member - 2 Years
    Replies: 550
    Topics: 41
    #271615

    7414 is slightly thicker 0,188″  Should work OK ,but, will need to be seated slightly deeper in pocket to be flush. It would have to be touchy application for 0.032″ difference in seal thickness to affect situation. I would still go with 7415 when sourcing a seal. I have used general industrial 7415 and have tried NAPA version intended for use in automobile transmission. The shell of NAPA did  not appear as robust or corrosion resistant.  I believe that for the limited use a restored motor might receive that corrosion resistance is the important consideration.

    so it seems to me

    Louis


    Buccaneer

    US Member - 1 Year
    Replies: 6452
    Topics: 958
    #271624

    7414 is slightly thicker 0,188″  Should work OK ,but, will need to be seated slightly deeper in pocket to be flush. It would have to be touchy application for 0.032″ difference in seal thickness to affect situation. I would still go with 7415 when sourcing a seal. I have used general industrial 7415 and have tried NAPA version intended for use in automobile transmission. The shell of NAPA did  not appear as robust or corrosion resistant.  I believe that for the limited use a restored motor might receive that corrosion resistance is the important consideration.

    so it seems to me

    Louis

    Louis, I have plenty of clearance above the seal with the points cam seated,
    but saved your notes for “next time”. Thanks!

    DSCN5881

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    • This reply was modified 1 week, 1 day ago by Buccaneer.
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    crosbyman

    Canada Member - 2 Years
    Replies: 2991
    Topics: 287
    #271628

    cover up the  exposed surface of the seal with a couple of  latex glue coats  or epoxy  for improved corrosion resistance.

    Joining AOMCI has priviledges 🙂

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