force 90 fit a 120 force

G

goldsuke25

Cadet
Joined
Apr 8, 2009
Messages
18
will a force 90 lower unit fit a 120 force it looks identical
but i am not that savy on this also what are the differnce

I have a 120 force 95

any help would be appreciated
 
HAV2FISH

HAV2FISH

Chief Petty Officer
Joined
Oct 24, 2008
Messages
519
Re: force 90 fit a 120 force

What year is the 90 and what year is the 120?
Are the shaft length the same?
Are the splines on the shaft the same?
If there all the same, then the 90 lower unit will fit.
The 90 might have a different gear ratio so you might have to change your prop pitch.
 
G

goldsuke25

Cadet
Joined
Apr 8, 2009
Messages
18
Re: force 90 fit a 120 force

mine is a 20 inch, so is his ,mine is a 95 120,his is a 96 90

a couple of quistions? how do you know what your shaft length is
when the lower unit is off ?were do you measure from ?also would a 25 inch fit a 20 inch? what does it mean to adjust the prop pitch ?a basic of how it is done .I am not forsure if mine is a 20 inch or not I took it off and it seems in the middle when i measure it from the top of the water pump housing it is 19and a half .with the pump housing off it is aprox 23 inches before it goes in the casing.
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,665
Re: force 90 fit a 120 force

Welcome to iboats.

Shaft length is not measured on the actual drive shaft.

It is measured from the transom bracket to the antiventilation plate.
Click the picture below for details.

Sorry, a 25" will not fit a 20".


You don't change the pitch of the prop, you buy a different prop with the correct pitch.
There is info in the "prop forum" that will explain how to choose the correct prop.

http://www.iboats.com/ref/images/shaft_length_small.gif
 

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R

RRitt

Captain
Joined
Mar 30, 2006
Messages
3,319
Re: force 90 fit a 120 force

If the boat came with 20" shaft engine then why couldn't you put on a 25"?
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,665
Re: force 90 fit a 120 force

He doesn't want to switch to a 25" motor.
He wanted to know if a lower unit from a 25" motor would fit on a 20" motor.

Technically, he could put it on, but would have to swap out the driveshaft, and shift rod.
 
G

goldsuke25

Cadet
Joined
Apr 8, 2009
Messages
18
Re: force 90 fit a 120 force

thanks for the help one more thing will it change the performance
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,665
Re: force 90 fit a 120 force

it shouldn't, unless the gear ratio is different
 
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