Home › Forum › Ask A Member › 50’s 18hp OMC retrofit question
- This topic has 25 replies, 10 voices, and was last updated 4 years, 12 months ago by dan-in-tn.
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April 14, 2019 at 9:02 pm #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
April 15, 2019 at 1:43 am #173413Swapping out with a low ’70s 25 horse powerhead should work . . .
April 15, 2019 at 5:25 am #173414Wanna 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.
April 15, 2019 at 5:52 am #173416Swapping out with a low ’70s 25 horse powerhead should work . . .
Excellent, thanks I did not know that was possible!
April 15, 2019 at 5:59 am #173417Wanna 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
April 15, 2019 at 6:11 am #173418I 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 5 years ago by rudefan29070.
April 15, 2019 at 9:03 am #173425As 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
April 15, 2019 at 9:34 am #173431There was a change in the powerhead base mounting pattern around 1960-ish. Not sure they can be interchanged, or not.
April 15, 2019 at 9:55 am #173432Where 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
April 15, 2019 at 10:44 am #173439Well, 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 Chapteruccaomci.com
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