18 hp evinrude. 1958

So I just bought my first aluminum boat and it didn't come with a motor. I found an 18 hp evinrude on craigslist that looked to be in good condition and ran good. I went ahead and bought it for $300. The guy told me he just had it serviced with new plugs and wires, a coil, carb rebuilt and new gear oil in the lower end. My concern is that he didn't know what year it was and once I researched it I found out it's a 1958. Does anyone know if these are typically good motors and what I should watch for? Also can I get rid of the pressurized fuel tank?

Congrats,your gona love that motor,Its among the best that omc ever built.Tougher than nails,lightweight for the HP.If the presurized tank is in good shape I,d leave that way.If you absolutely want to convert it to regular tanks,theres a way you have to install a pump on your motor mecanics say its simple as for me its complicated,,,theres abook that describes how to do it its called (Cheap Outboards) written by Max E.wawrzyniak III .Good luck,youve got yourself a great motor. Mike

Great motor I have a 1955 15hp evinrude fastwin, its been good to me. If you were closer to me you could have picked up mine for $200. Pressure tanks are ok, I had to go over mine and install all new clamps but it works great. You can convert them to regular I think its pretty much changing the air pump to a fuel pump but Im not 100% sure on that I saw it online once. The only Thing I dont like is when your done and you vent the tank it lets out alot of fuel vapor so dont smoke when you vent it.

Thats good news. I was worried the motor was too old. Thanks for the info.

I've heard nothing but good things about that motor. Take some time to learn as much as you can about outboard maintenance. The antique outboard motor forum is a good resource for info.

edit: Oh, I forgot to mention. You can look-up parts/diagrams here...
https://www.marineengine.com/parts/johnson-evinrude-parts.php

good buy and great motor...I had one for years. the only thing I had trouble with was the bolts at the carb. would not stay tight..constant problem...The other thing is, Is I believe that is one of the last "CAST IRON" motors...Mine was oh so heavy..
use it well and have fun.
peace
Ron

There are a couple of ways to convert to a fuel pump and get rid of the pressurized tank......You decide which way you want to do it.


https://www.duckworksmagazine.com/05/columns/max/5/index.cfm


https://www.sschapterpsa.com/ramblings/Converting_dual_fuel_line.htm

When he is talking about the side plate he is referring to the bypass cover. He forget to mention to plug off the exhaust manifold nipple that supplies air to the pressurized tank.


This is electronic parts diagram for your motor. 1958 18hp (look on page 4 item number 30 ) bypass cover

https://www.marineengine.com/parts/vintage-evinrude-johnson/ITEM_2922/catalog.html?https://www.marineengine.com/parts/vintage-evinrude-johnson/ITEM_2922/ITEM_292200001.htm


This is an electronic parts diagram for a slightly newer motor 1960 (look on page 6 item number 39) bypass cover that can accommodate a fuel pump.
https://www.marineengine.com/parts/vintage-evinrude-johnson/ITEM_3038/catalog.html?https://www.marineengine.com/parts/vintage-evinrude-johnson/ITEM_3038/ITEM_303800001.htm


Here is another explanation. This was posted by a member on the iboats forum

OMC converting 2 line pressure to 1 line fuel pump

i've been ask numerous times how i converted my 1958 35 seahorse from the pressure tank, to the fuel pump to work with the single line tanks.

disclaimer: this is for a 1958 35 hp johnson seahorse. you have to verify your on parts, and method of conversion. i will not be responsible for any screwups.

i started by ordering fuel pump 438562, bypass cover gasket for this engine 304784, and fuel connection 438793. you will have to verify the bypass cover gasket for your particular engine.

i remove existing connections, & bypass cover. had the 2 outer hole tapped for 10/24 bolts, and the center hole drilled out (this is for the pulse, to operate the pump) reinstalled cover with new gasket. mounted fuel pump to cover(don't forget gasket between cover and pump).

removed existing fuel connector, and replace with new. install new fuel line from connect to pump, will have to be bigger diameter to fit connections.

new fuel line from fuel pump to carb. and i just use the shade tree mechanics method of blocking the air line with a bolt into the line with a hose clamp.

make sure everything is tight. connect fuel line, and should be ready to run.

Click to expand...

My suggestion is go to AOMCI forum ( https://www.aomci.org/cgi-bin/yabb2/YaBB.pl )

Go under ask a member and they would certainly walk you through it if you have any doubts. They may try to convince you to keep the old pressurized tank system, because some of the guys are purest about the old motors, but just politely and patiently state that would feel better about the single line fuel pump system conversion. There is a lot knowledge about your 1958 motor on that forum. You can also post a want ad on that forum for the bypass cover for the 1960 to 1962 18hp model that will accommodate a fuel pump. Please ask them what current fuel pump would be acceptable.


Good luck and be carefully. Before you buy all kinds of parts and stuff verify stuff with AOMCI guys.

Congrats on a great acquisition! I have the exact same motor. You did well getting a working motor and tank for $300. I paid $150 for mine but had to invest another $900 to get it working. Still, no regrets. She runs beautifully and should last me another 50 years! I get tons of compliments on my motor. The new ones just don't have any style.





You should be able to find all the parts/info you need at https://www.marineengine.com

Another good resouorce for paint and decals is https://www.nymarine.com

You can get rid of the pressurized tank by installing a fuel pump. However, I run the pressurized tank and don't see any need to switch to a pump.

Let's see some more pics of your motor!

Cheers,
BC

No reason to get rid of the double line gas tank! The second line just pressurizes the tank and pushes the fuel to the carb. Super simple design and has worked for 52 years problem free so far. Can't say that about a diaphragm fuel pump with todays gasolines.
I will add some information that others so far have not.
First, that engine must run on no less than 24:1 fuel/oil ratio, nothing less for wear purposes. You WILL wear the piston skirts and cylinder walls much faster on a leaner mix as that engine was built with materials and clearances that simply needed additional volume of oil to seal and lubricate it. It can run as much as 16:1 or 20:1 if you want but never any less than 24:1. Chances are that is printed on the inside of your cowling. The use of todays modern oils do not allow any leaner mixture no matter what anyone says. You will not foul plugs at that mixture. The addition of a diaphragm fuel pump also does not mean you can run leaner mixtures.
Ignition system should be checked to make sure newer style coils are in it. Water pump impeller should be replaced. Gearcase oil should be checked often until you are sure no seals are leaking water into the gearcase.
If you can, run fuel that has no alcohol in it. You can ask marinas in your area if they supply it or know where you can find it. Not that you have to but it is alot easier on the rubber parts in the carb and will not destroy a diaphragm fuel pump as fast as alcohol extended fuels will. Also it has no affinity for water like alcohol fuels do so you won't find your 6-gallon can with a half gallon of water at the bottom of it if left for a while. Enjoy that little gem and take care of it and it will take care of you! You will start many a conversation at the boat ramp with that one! I am sure Baitcaster has with that one he has!

Ok guys....I was not trying to convience him to change over to a single line. I have a a motor that requires a pressurized tank and it runs fine. If he wanted to change over to a single line system, I was just trying to give him some good guidance.

I have a Evinrude 7.5hp 1955 motor that has a pressure tank system and I plan on leaving it just like that. It runs just fine on the pressurized tank

Thanks for the resources I appreciate it. I will try and get some more pics posted.