120 vs 125 force

[fisheymikey]

i have the opportunity to pickup a force1 20 1991 for 450$ but the bottom cylinder compression is 0.

my question is my engine so far is running good just wanted to know as per parts i,e
trigger,cdm,stator are they the same? i have read somewhere that the cykinder of the 120 is actually bigger therefore also is a bit stronger than my 125.

what say u? what would you do?

 

[ferdly1]

What I would do is get year and model number from motor you want to buy. Go to I boats parts website and compare part numbers. I found certain parts off my 40hp fit my 75hp by doing that. Make sure both motors are 3 cyl.or 4 cyl.

 

[pnwboat]

In 1989 and earlier the 125HP motors used 3.312" standard size pistons. In 1990, the 120HP/125HP motors used both 3.312" and 3.375" standard size pistons. Starting in 1991, they 120HP motors used 3.375" Pistons. You won't notice much, if any difference between the 125HP 3.312" motors and the 120HP 3.375" motors. Your 1989 or earlier 125HP motor uses the Prestolite Ignition system. If the 120HP motor is an early production motor, it may use the Prestolite ignition system, otherwise it uses the Mercury SwitchBox ignition system. None of the ignition components are interchangeable between the Prestolite and Mercury SwitchBox ignition system.

 

[jerryjerry05]

The 125's were rated at the head'
I think the 120 was at the prop.
Different pistons. Basically the same motor.

Make sure it's the same length 20 or 25"

For that price I'd buy if it had 2 bad pistons.

 

[fisheymikey]

well thats what i thought..

gonna finish my week of work and see if i have some extra cash... then we buy

​thanks guys for the advice

 

[Frank Acampora]

First, the 125 was rated at the prop. ANY force engine after 1984 (and any Chrysler after 1984 before sold to Brunswick) was rated at the prop. Second: I can't prove it because I never compared the 120 to the 125 BUT because of the bigger bore of 3 3/8 --theoretical horsepower is mathematically figured using bore size--I always considered the 120 to be a better engine. Indeed. later models of the 120 when Mercury started modifying them used longer connecting rods for less piston side thrust and other theoretical advantages. They were real powerhouse engines. Not to discount the 125, I had one on my 14 foot test bed and it went 55 MPH at 5900 RPM. On my 21 foot cuddy it delivered 33 MPH. An increase of 25 HP to 150 drove the hull to 40-43 MPH. The five cylinder engine are also real powerhouses.