Replacing mercury 90hp with Johnson 90hp

ib18

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Do I need to drill new holes if I want to replace a mercury 90hp with a Johnson 90hp outboard motor?

Both have power trim and tilt.

Please help!
 

emdsapmgr

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Re: Replacing mercury 90hp with Johnson 90hp

The bolt hole spacing should be the same.
 

Bosunsmate

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Apr 7, 2012
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Re: Replacing mercury 90hp with Johnson 90hp

Probably.
Lots of different models that fit this 90hp category
 

Bosunsmate

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Re: Replacing mercury 90hp with Johnson 90hp

Ps mine was a guesstimate, take the admirals word for it
 

Chinewalker

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8,902
Re: Replacing mercury 90hp with Johnson 90hp

Depends on the year of the 90 Merc. Mercury was kinda late coming to the BIA standard for the bolt patterns, with some models not being converted until the 1980s.
 

ib18

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Re: Replacing mercury 90hp with Johnson 90hp

here is the pic for my mercury 90hp with power tilt on the boat transomIMG_2902.jpg

Top 2 screws are 13" apart
Bottom 2 screws are 10" apart
Top to bottom screw are 10" apart

will pick up my johnson 90hp this weekend
 
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boobie

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Re: Replacing mercury 90hp with Johnson 90hp

Should be no problem fitting.
 

jimmbo

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Re: Replacing mercury 90hp with Johnson 90hp

That merc has the same pattern as the Johnson

Merc started using that pattern in 1984 on the 4 cylinder 75hp and the I6s, in 1985 the V6s also started using it
 

ib18

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Re: Replacing mercury 90hp with Johnson 90hp

1987 Mercury 90 hp 2 cycles 3 cylinder outboard (Serial No: 0B194831 Model No: 1090727)

I think the Johnson 90hp is a 1982. Is it going to fit?

Model # J90MLCNB
J5686362

Johnson1.jpg
pic2
Johnson2.jpg
pic3
Johnson3.jpg
pic4
Johnson4.jpg
 
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racerone

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Dec 28, 2013
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Re: Replacing mercury 90hp with Johnson 90hp

Has the compression been checked on this 1982 motor ??--------Looks like it has been used a lot.
 

emdsapmgr

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Re: Replacing mercury 90hp with Johnson 90hp

Have you got an OMC control box for that 82?
 

ib18

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Re: Replacing mercury 90hp with Johnson 90hp

yes, got the control box with key (almost forgot to ask for it). had to drive back to get the key for the control box. will measure the cable to see if i can use it for my boat

had a scary moment to hoist the motor out of seller's crab boat - almost sunk the motor, the hoist and his crab boat - lol

see video - engine hoist almost fell into the sea - YouTube
 

emdsapmgr

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Re: Replacing mercury 90hp with Johnson 90hp

Your compression numbers are strong for that engine.
 

ib18

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Re: Replacing mercury 90hp with Johnson 90hp

Wow, good to hear that 110 psi is good for my Johnson 90hp considering it is a 1982 motor (32 years old). I just need to wash it down, so much salt and rust on that motor, change the impeller, buy a spark plug wire 12". The head was broken.
ordering parts tomorrow.

https://www.youtube.com/watch?v=2meWri0t5LU
 

emdsapmgr

Supreme Mariner
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11,551
Re: Replacing mercury 90hp with Johnson 90hp

You might want to also consider replacing the two thermostats. A good PM item, esp since you are a new owner. They are not expensive and relatively accessible on that engine.
 

racerone

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Re: Replacing mercury 90hp with Johnson 90hp

This may be a salt water motor ??------------There could be issues with bolts breaking on that thermostat housing.---------Looking at the transom of this boat I am not sure if I would want to go far from the dock with it.----Has the condition of wood in the transom and stringers been checked ????
 
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ib18

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Mar 2, 2013
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489
Re: Replacing mercury 90hp with Johnson 90hp

ya, thanks for the transom warnings. I may need to rebuild the transom. Will take a good look after I detach the mercury motor mid section from the boat and post the pic and video and ask for help again.
 

ib18

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Mar 2, 2013
Messages
489
Re: Replacing mercury 90hp with Johnson 90hp

Not sure if this the right rebuilt kit?

P/N 13270 Thermostat Rebuilt Kit
143 degree for V4 Crossflow
Kit contains
2 # 13010 434841 Thermostat
2 # 46170 318395 Valve
2 # 46150 317245 Spring
2 # 86481 321692 Grommet
2 # 33650 332369 Gasket
2 # 34440 321932 Gasket $26.89
 
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