Late 50's Johnson 18 hp compression?

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Buccaneer
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Late 50's Johnson 18 hp compression?

Postby Buccaneer » Fri May 18, 2018 3:20 pm

What would be acceptable compression on a circa 1958
Johnson 18 hp? Some kid wants to use it as a partial trade
on a motor I have. It looks like it's been on that pontoon
boat since water was invented.
Thanks,
P.S.- in looking at the photos I'm wondering if it's older yet?
Almost looks like a green Johnson under that maroon!
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1958 Johnson 18 hp.jpg
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Mumbles
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Re: Late 50's Johnson 18 hp compression?

Postby Mumbles » Fri May 18, 2018 4:11 pm

It's hard to tell from this angle but I think it's a '57 hood sitting on it with an Evinrude gearcase.
Still searching for a rudder and hardware to fit a KOBAN. ☺

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Chris_P
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Re: Late 50's Johnson 18 hp compression?

Postby Chris_P » Fri May 18, 2018 4:15 pm

Its a '57 Johnson. Like Mumbles pointed out, looks like the gearcase MIGHT be different. If I had to bet I would bet on Evinrude due to the prop on it.

That green that you see is the chromate primer.

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Buccaneer
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Re: Late 50's Johnson 18 hp compression?

Postby Buccaneer » Fri May 18, 2018 4:45 pm

Thank you knowledgeable gentlemen!
Don't think I'd credit him a whole lot
on the trade, but I suppose it has potential!

fleetwin
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Re: Late 50's Johnson 18 hp compression?

Postby fleetwin » Fri May 18, 2018 5:41 pm

Yeah, looking to be a 1957 model. Sure looks like it has had a hard life indeed, especially on that stupid pontoon rig. I'm guessing you should see around 100PSI for compression. I would check/drain the gear lube also, look for water. Pontoon duty may have really messed up the clutch dog/forward gear as well....

Chris_P
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Re: Late 50's Johnson 18 hp compression?

Postby Chris_P » Fri May 18, 2018 6:12 pm

Forgot about your main question!

Definitely the 18s are over 100 psi on a good motor. I have literally had hundreds of the 18s. Not uncommon for good ones to have over 120 psi.

My GUESS is new they have around 140 psi. I have one motor that is almost NOS. Ran very little. It is a 1957 Evinrude 18hp. The bores still had original cross hatch. All I did was install new rings, at it was sitting at 140psi.

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Buccaneer
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Re: Late 50's Johnson 18 hp compression?

Postby Buccaneer » Fri May 18, 2018 6:58 pm

Thanks again for the compression info. The kid came to buy my
motor, but didn't bring the 18 hp Johnson for trading.
Said he decided he'd need some help to get it off the pontoon,
and didn't have the right tools at the cabin. :?
He said he'd call me when he gets if off, but I wont hold my breath!

Theodore
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Re: Late 50's Johnson 18 hp compression?

Postby Theodore » Fri May 18, 2018 9:57 pm

A young man taking an interest in old outboards? I would go out of my way to help him. Just like someone did for me long ago......

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hdted
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Re: Late 50's Johnson 18 hp compression?

Postby hdted » Sat May 19, 2018 4:51 pm

I had a 1974 25hp NOS motor still in the box. It had 140 psi cranking pressure. I don't know if there was a difference between the 18 and 25, but they were both 22 Cubic inch motors.

outbdnut2
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Re: Late 50's Johnson 18 hp compression?

Postby outbdnut2 » Mon May 21, 2018 12:49 pm

That green peeking through could be an old camoflage paint job for duck hunting that was later painted over. Hard to tell from the photos.
Dave


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