'57 Johnson 7.5 HP Project

southkogs · Aug 13, 2013

Hi all:

I'll get some photos up later, but for the moment I have a couple of basic "where do I start from" questions:

Background: I picked up my great-grandfathers Johnson 7.5 and brought it home this weekend. It's been in a family garage for several years and hasn't been started for just slightly under that long. When it was put up, there were two reasons carb problems (not sure exactly what) and the pressure tank was leaking.

I'm 98% sure it's a '57, but I haven't confirmed that yet (haven't located a number on the motor). But looking through some threads here on iBoats, talking to my dad and some old literature I'm pretty sure it's a '57.

Question #1: The pressure tank leaking will be a problem later, but if I don't mind a little fuel leak for the time being do I need to fix that right away? If so, is it better to just get a new tank or can your rebuild 'em rather easily? (main leak I think is at the pump "knob" on top of the tank)

Question #2: I've seen a couple of detailed threads on converting over to a single line tank with a fuel pump. How critical is that from a safety standpoint? I ran this motor as a kid and it's never hinted at a safety issue, but I don't want to make assumptions.

It's in the garage waiting for the weekend which is when I'll get the first chance to tinker with it.

Thanks in advance.

Scurvy Knave · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

Hi

I have the evinrude version of that in a 54 model year. Great motors.

Regarding question #1. At least change the hoses to ethanol resistant hoses. You can get rebuild kits for the tanks - I think it's pretty straightforward to. If the tank can't keep pressure you will have to constantly pump the tank by hand to keep the motor running. not very useful.

question #2. conversion isn't hard (or so I'm told) but I see no reason to do it unless your pressure tank is busted and you can't locate a new one. Plus, by keeping your motor on the pressure tank, you don't risk connecting it to a tank with too little oil in it. Remember, that engine needs 16:1 mix (one quart in one gallon)

HighTrim · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

As stated, finding a rebuild kit is as easy as doing the job itself. Done plenty. You cannot run the motor if it doesn't hold pressure. It will need to be rebuilt. Before rebuilding, ensure it is sound and not rusted or you are wasting your time/money.

Converting is also a quick easy process. If you have other motors that run on a single line tank, may be easier. Pressure tanks are not dangerous though, I have about 50 of them, and know hundreds of guys in the aomci club that run them and have never heard of one blowing up like some articles will make you believe.

nwcove · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

^^+1 carefully inspect the tank....inside and out. a bit of surface rust is usually ok, but any pitting may be cause for weighing your options on a replacement pressure tank or converting. ( you can barrel run the motor with the existing tank tho, you just need to elevate the tank so its above the carb, and prime as usual....gravity feed will take over from there)

southkogs · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

Great answers, thanks y'all.

I'll get into it some more this weekend and get a look at what kinda' shape it's in. Got a lotta' cleaning to do on it anyway. Plus ... stupid job keeps gettin' in the way, so it'll be a little while in getting her up and going. If it runs well enough, then I gotta' find something to put it on

It's got roughly the same motor cowl as in your avatar, nwcove.

I'll get some photos going in the next week and start monkeying with it.

nwcove · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

heres a couple of pics of my 58 7.5 .you gotto to love those cowls!!!! and those motors run like a sewing machine when properly tuned.

HighTrim · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

Here is a '56, cannot find pics of my '57

southkogs · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

nwcove said:
...you gotto to love those cowls!!!! and those motors run like a sewing machine when properly tuned.

The styling on these motors is what makes 'em so much fun. We've also got an older Evinrude 3HP up there (I'm thinking it's more like a '54 or earlier), and I may work with that one next summer. I always remember this motor running like a champ. I'm kinda' thinking if it really is just a carb issue, it may crank up easy.

HighTrim said:
Here is a '56, cannot find pics of my '57

View attachment 207754 View attachment 207755

Thanks HighTrim - the '56 has the "medallion" with the HP designation (at least in all the literature, and it's holding constant on yours). The '57 has it painted on like Cove's '58, but in white on red (same color scheme as yours) - and that is what I have.

ddwilson · Aug 13, 2013

Re: '57 Johnson 7.5 HP Project

I have a 58 10hp rebuilt the carb when I got it along with replacing the impeller (Which I would highly recommend that you do since it has
been setting for a while) another fairly easy job. The carbs on these motors are pretty simple and easy to clean up and rebuild. If the pressure tank is not rusty it is easy. Take the top off remove the cotter pin on the primer button and it should slide apart. Replace the gasket on the window for the fuel gauge, new o ring on the primer and put he new diaphragm an cork gasket on the base. While it is apart might at least check the points. If it has fuel and spark and some compression should start right up. I never have to pull mine more than usually 1 time, if it sets for a few weeks may have to pull it twice. They really are great motors and look good too.
Doug

southkogs · Aug 17, 2013

Re: '57 Johnson 7.5 HP Project

Got it out and did some lookin': what I think is the SN is stamped into (what I think is) a freeze plug -

SN: 1497570 - making it a '57, correct?

It's all a little dirty on the outside, but the motor itself looks pretty good.

Haven't tried starting it yet. I'm gonna' check fluids and clean it off first. Any other pre-"pullin' the cord" stuff I should do? I know dad winterized it before it was put up (I can see his "tell-tales" with plugs and such), but don't know much else yet.

The tank looks dirty with some surface rust, but nothing that won't clean off easily. The bottom of the tank really has no rust and looks MUCH better than the topside.

I'll keep playin' today a little. I've got a few other projects to do outside before we go toss the boat in the lake for a few hours.

Thanks all.

southkogs · Aug 17, 2013

Re: '57 Johnson 7.5 HP Project

Found the model number: AD-11

HighTrim · Aug 17, 2013

Re: '57 Johnson 7.5 HP Project

Yes she is a very early 1957.

How long has she been sitting?

southkogs · Aug 17, 2013

Re: '57 Johnson 7.5 HP Project

HighTrim said:
...How long has she been sitting?

I'd say at least 10 years, but I'm not 100% positive. I know that we replaced it on the boat in the mid 90's, but I don't know how much anyone has monkeyed with it since.

Got some cleaning done this afternoon:

It'll be a week or two before I can do much else. Got a trip to Charleston this coming weekend.

HighTrim · Aug 17, 2013

Re: '57 Johnson 7.5 HP Project

In 10 years the rubber components could have dry rotted.

I would change the gear oil.

Compression test for future base lines.

Open the carb and rebuild/clean as needed.

Change the fuel lines.

Verify spark and ensure it jumps a 1/4" gap on a tester with a bright blue ZAP!! Attend to ignition as needed.

Regrease and oil.

southkogs · Aug 17, 2013

Re: '57 Johnson 7.5 HP Project

Thank you sir! Will report back as we move along.

southkogs · Aug 18, 2013

Re: '57 Johnson 7.5 HP Project

SO ... any good part sources out there? In all the places I look, I can only find parts back through 1968. I've only Googled for about 1/2 hour, so I might be missing something ...

... and if I just need to hit eBay or CL, I can do that too.

HighTrim · Aug 19, 2013

Re: '57 Johnson 7.5 HP Project

What in particular are you looking for?

1946Zephyr · Aug 19, 2013

Re: '57 Johnson 7.5 HP Project

From looking at that cylinder head, it looks like it may have gotten pretty hot. If your compression numbers are good, then you'll be okay. Nice looking motor. I have the 5.5 that is a perfect match to yours.
A lot of your tune up parts should be obtainable at your local marine supplier. The same impeller was used in the 6hp up till 1979 Points and condensors as well, are easy to get.

southkogs · Aug 19, 2013

Re: '57 Johnson 7.5 HP Project

HighTrim said:
What in particular are you looking for?

I know I'm going to need some carb parts (not sure which yet). If memory serves, that's what brought her off the water. I also would like to get the pieces and parts to rebuild/repair the pressure tank (wondering about converting the tank lines to ethanol resistant as mentioned early in the thread). And - the impeller for sure.

I was basically lookin' a little to start pricing more than ordering - though a coupla' things I'd order right away.

1946Zephyr said:
From looking at that cylinder head, it looks like it may have gotten pretty hot. If your compression numbers are good, then you'll be okay. Nice looking motor. I have the 5.5 that is a perfect match to yours.
A lot of your tune up parts should be obtainable at your local marine supplier. The same impeller was used in the 6hp up till 1979 Points and condensors as well, are easy to get.

Thanks Zephyr - marine shops are kinda' sketchy here in my area. There are a couple of decent mechanics, but haven't found a GOOD all around marine supplier locally. I can call around some though.

AlTn · Aug 19, 2013

Re: '57 Johnson 7.5 HP Project

marineengine.com offers many items back to 1956

'57 Johnson 7.5 HP Project

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