Scott-Atwater 30HP lower unit seals

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    US Member - 2 Years
    Replies: 287
    Topics: 46

    Before I pull out my calipers and make a ham-handed effort at measuring seals, has anyone had any luck matching Scott-Atwater lower unit seals to current seals by SKF? I am working on a 1956 Firestone 30HP, which has the same lower unit as the 1955 Scott-Atwater badged 30HP and the 1956 S/A 33HP. NAPA/Sierra used to make a lower unit seal kit (18-4810), but I haven’t been able to track one down. The two oil seals on the lower unit that I need most are:

    Prop Shaft Seal – original part 3654-3109
    Drive Shaft Seal – original part 3654-3186

    Every other seal in the lower unit is an o-ring, so I am less concerned about tracking those down. I know this is a long shot, but I appreciate any info anyone has on these tough-to-find parts.



    US Member - 1 Year
    Replies: 493
    Topics: 47

    Hi Jason, Best I can do is the Sierra nos for your seals are 18-2127 for the driveshaft seal, and 18-2132 for the prop shaft. I don’t have anything that crosses to seal makers…And these are OLD numbers, I found one of them is already reassigned to as trim hose..

    • This reply was modified 6 days, 19 hours ago by Avatarretiredoz.

    US Member - 2 Years
    Replies: 287
    Topics: 46


    Thanks so much … that is a big help!

    It looks like Scott-Atwater may have been using Chicago Rawhide (CR) as their supplier, as upon close inspection of the seals, they both had CR numbers stamped into them. I typed the numbers in SKF‘s online CR interchange tool ( ) and was able to find current SKF part numbers, which I also cross referenced to Timken. Here were my results:

    Drive Shaft Seal
    SKF 6903 (original CR 11120)
    Timken interchange = 450009

    Prop Shaft
    SKF 10049 (original CR 1831)
    Timken interchange =450593

    With those and your Sierra numbers, I now have some options to go shopping! It’s nice that there is some hope for guys looking for Scott-Atwater seals if they were using CR seals.

    Thanks, again, for your help. Always good to hear from you, too. (This is my first post in a long time.)

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