50’s 18hp OMC retrofit question

Home Forum Ask A Member 50’s 18hp OMC retrofit question

This topic contains 19 replies, has 5 voices, and was last updated by Avatar shoestringmariner 2 days, 14 hours ago.

Viewing 15 posts - 1 through 15 (of 20 total)
  • Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173404

    Hey folks, I’m wondering if my 1957 18hp Johnson’s internals can be upgraded with internals from motors of later years like I believe the 58 QDs can? If not 57, than 58?

    What about 25-30 hp’s Up to 58?
    I would like to get away from 16:1 ratios but keep an iconic motor on my 1957 wooden runabout.

    One outing with my 57 and the transom is covered with a grey oil film.

    Thanks in advance

    Avatar
    garry-in-tampa
    Lifetime Member
    Replies: 3008
    Topics: 29
    #173413

    Swapping out with a low ’70s 25 horse powerhead should work . . .

    frankr
    frankr
    US Member - 1 Year
    Replies: 3996
    Topics: 43
    #173414

    Wanna start a fuel mix war? You say your goal is to get away from 16:1 mix. In the first place, 24:1 is the correct mix for your ’57. Now for the war: Show me the difference between the ’57 guts and something like ’70, which is a 50:1 motor.

    Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173416

    Swapping out with a low ’70s 25 horse powerhead should work . . .

    Excellent, thanks I did not know that was possible!

    Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173417

    Wanna start a fuel mix war? You say your goal is to get away from 16:1 mix. In the first place, 24:1 is the correct mix for your ’57. Now for the war: Show me the difference between the ’57 guts and something like ’70, which is a 50:1 motor.

    Oops, my bad, I was thinking about my TN28’s. But yes, 24:1 is too rich and 50:1 is what I’m trying to achieve.

    And not trying to start a fuel war, I’m just trying to clean mine up is all

    Avatar
    rudefan29070
    US Member - 1 Year
    Replies: 13
    Topics: 4
    #173418

    I just recently have poured over parts for ALL the years of 18’s looking for pistons for my rebuild. Frank is right there isn’t much difference in them at all. If I had a 1950’s era 18 I would surely run a leaner mix than 24:1. The oils we have available today are MUCH better. I have a 1968 18 that I run basically a 50:1 mix and I throw in 1 more oz for a 6 gallon tank, instead of 16oz of oil per 6 gallons I mix 17. The motor doesn’t complain and it runs like a cat kicked in the butt and doesn’t foul plugs. My best friend has a 1965 18 that I maintain and he too runs the mix I do and doesn’t have any trouble with his either. We both run the Johnson Evinrude TCW3 2 stroke oil that they sell at Walmart by the gallon.

    • This reply was modified 3 days, 14 hours ago by Avatar rudefan29070.
    Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173425

    As it so happens, I happen to have a 1969 18hp that could work. I’ll probably use my 57 until I pick up a 58 since I prefer that colour scheme.

    My 57 runs so good it would be a shame to cut it up

    frankr
    frankr
    US Member - 1 Year
    Replies: 3996
    Topics: 43
    #173431

    There was a change in the powerhead base mounting pattern around 1960-ish. Not sure they can be interchanged, or not.

    Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173432

    Where do you guys get your sources when it comes to parts diagrams? If I could look those up I could look through them to see if I can determine what years are compatible.

    This junction, I think I’d rather go 25 or 30 horse if I’m going to all this work. Electric start if available in those years will be nice too as this runabout is dual cockpit without a pass-through. Kind of awkward to get back to the motor

    Avatar
    wbeaton
    Canada Member - 1 Year
    Replies: 584
    Topics: 65
    #173439

    Well, you aren’t going to get 25-30 hp out of that 18 hp without swapping power heads and I don’t believe any 25-30 powerhead that will swap. At best you could swap in a 70’s 25 hp powerhead, but I don’t think it will be easy. Plus it won’t have the mounting points for the cowl.

    24:1 shouldn’t be as messy as you are experiencing. If it’s still too dirty and you aren’t willing to use 50:1 then I suggest finding a newer motor in the hp range you want. I don’t mean that to sound harsh. I just don’t see an alternative.

    Wayne
    Upper Canada Chapter

    uccaomci.com

    • This reply was modified 3 days, 10 hours ago by Avatar wbeaton.
    • This reply was modified 3 days, 10 hours ago by Avatar wbeaton.
    frankr
    frankr
    US Member - 1 Year
    Replies: 3996
    Topics: 43
    #173442

    Where do you guys get your sources when it comes to parts diagrams? If I could look those up I could look through them to see if I can determine what years are compatible.

    This junction, I think I’d rather go 25 or 30 horse if I’m going to all this work. Electric start if available in those years will be nice too as this runabout is dual cockpit without a pass-through. Kind of awkward to get back to the motor

    Some people collect motors. I collect parts books (and a few motors). I have piles of parts books stored on my computer.

    For others, marineengine.com is a very popular resource, as well as the Evinrude website.

    Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173457

    U

    Well, you aren’t going to get 25-30 hp out of that 18 hp without swapping power heads and I don’t believe any 25-30 powerhead that will swap. At best you could swap in a 70’s 25 hp powerhead, but I don’t think it will be easy. Plus it won’t have the mounting points for the cowl.

    24:1 shouldn’t be as messy as you are experiencing. If it’s still too dirty and you aren’t willing to use 50:1 then I suggest finding a newer motor in the hp range you want. I don’t mean that to sound harsh. I just don’t see an alternative.

    Thanks.

    I don’t want to get 25-30hp from an 18 hp. To get that power, I will ditch the 18hp and go with a 25-30 hp motor build. So it’s either those swappable powerheads and or swappable internals (crank, rods etc) amongst these respective motors that I’m seeking info on. And I could always make custom mounting brackets for the cowl.

    It is possible that I was still running 16:1 instead of 24:1 as I had TNs at the time, which might explain the mess. But I’m still looking for ways to convert and run 50:1 IF possible.

    And your newer motor suggestion has merit; I recently saw a tohatsu 4stroke painted like a 50’s Johnny. Pretty cool.

    And I don’t mean to offend any purists. I see the value of restoration but I’m also the hot rodder type. Bone stock 57 Chevy or 32 Ford??? Not for me…Gotta hot rod them

    Avatar
    rudefan29070
    US Member - 1 Year
    Replies: 13
    Topics: 4
    #173459

    I have the Parts Catalog For my 1968. For all others I use the parts diagrams on Marineengine.com. Here is a website that sells some nice restored classic outboards. Their inventory updates regularly so keep checking. https://www.smalloutboards.com/antiques.htm

    Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173468

    I have the Parts Catalog For my 1968. For all others I use the parts diagrams on Marineengine.com. Here is a website that sells some nice restored classic outboards. Their inventory updates regularly so keep checking. https://www.smalloutboards.com/antiques.htm

    Perfect, thanks very much

    Avatar
    shoestringmariner

    Replies: 234
    Topics: 47
    #173469

    I have the Parts Catalog For my 1968. For all others I use the parts diagrams on Marineengine.com. Here is a website that sells some nice restored classic outboards. Their inventory updates regularly so keep checking. https://www.smalloutboards.com/antiques.htm

    Perfect, thanks very much

Viewing 15 posts - 1 through 15 (of 20 total)

You must be logged in to reply to this topic.