50’s 18hp OMC retrofit question

[frankr]

shoestringmariner wrote:

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.

[shoestringmariner]

U

wbeaton wrote:

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

[rudefan29070]

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

[shoestringmariner]

rudefan29070 wrote:

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

[shoestringmariner]

rudefan29070 wrote:

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

[wbeaton]

What I meant was there are no parts to swap either internal or external that will increase the hp of your 18 hp. The only complete powerhead swap that might work is a 1970’s 25 hp because it shares roots with your motor. Personally, I don’t care if you hot rod a 1950-60’s 18 hp. There is nothing rare or special about them. Enjoy the hobby the way you want. I’m just trying to save you some trouble and possible expense.

Wayne
Upper Canada Chapter

uccaomci.com

[garry-in-michigan]

I believe they went to the 50 to 1 ratio with the light tension “pressure back” piston rings. . .

[rudefan29070]

garry-in-michigan wrote:

I believe they went to the 50 to 1 ratio with the light tension “pressure back” piston rings. . .

And the pressure back was on the 2 ring pistons, right?

[shoestringmariner]

wbeaton wrote:

What I meant was there are no parts to swap either internal or external that will increase the hp of your 18 hp. The only complete powerhead swap that might work is a 1970’s 25 hp because it shares roots with your motor. Personally, I don’t care if you hot rod a 1950-60’s 18 hp. There is nothing rare or special about them. Enjoy the hobby the way you want. I’m just trying to save you some trouble and possible expense.

[shoestringmariner]

wbeaton wrote:

What I meant was there are no parts to swap either internal or external that will increase the hp of your 18 hp. The only complete powerhead swap that might work is a 1970’s 25 hp because it shares roots with your motor. Personally, I don’t care if you hot rod a 1950-60’s 18 hp. There is nothing rare or special about them. Enjoy the hobby the way you want. I’m just trying to save you some trouble and possible expense.

Where’s the like button?
I appreciate your thoughts and advice

[Author]

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