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Mercruiser 120 engine replacement proceedure

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boboa9

New member
Tomorrow, I'm swapping a mercruiser 120 engine (circa 1980) with the same from another boat.
Old engine data:
Mercruser 120 hp (circa 1998)
4 cyl, inline.
Eng No. V03121BA
SN No 2418299
The sterndrive is #2358060

I have the Clymer sterndrive manual but it does not talk about engine removal. It does describe in detail about rebuilding the stern drive including some special tools like a "puller kit" that lookls like it removes the bearing cartridge in the gimbal housing. Another special tool mentioned in the manual is an "engline alignment tool". No need to tear down the stern drive as I had it rebuilt recently. I just want to change motors.

What is the step-by-step process for extracting the motor and then installing the new(used) one? Do I need special alignment tools?
 
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the 98' must be a 3.0, not a 120 / 2.5.

The 80' could be a 120 / 2.5 or a 3.0.

Doesn't really matter, cause they are sister motors and use all the same external parts such as manifolds, risers, starters, etc. Just wanted you to know.

Ok the drive has to come off if it's a merc drive.

Ok i don't think the harness is the same. Me i would just remove the motor and leave the bell housing in place. That way you don't have to deal with the rear motor mount nuts, maybe rusted and a byatch to remove.

1- Disconnect the battery.

2- Every wire that won't let the motor move , starter,etc, has to be disconnected. Mark them so you will know where they go on the new motor.

3- The 4-5 screws that hold on the flywheel cover have to be removed.

4- The 5 screws / bolts that hold the motor to the bell housing must be removed.

5- Cable converter should be removed, carb cable disconnected.

6- Hook your hoist up, you got room to move the motor without removing the riser? If yes i use a strap around the riser, and lifting eye.

7- Remove the top nut off the front mount, or leaving the front mount connected to the motor remove the 2-4 bolts holding the front mount to the stringer. I leave the front mount in place and remove the top nut, then the motor goes straight up leaving the mount in place.

#7 is your call you may have to move the motor forward and up i don't know what clearance you have.

8- The rubber hose that connects the riser to the exhaust tube must be loosened at the exhaust tube. The large clamps just loosen them up. When the motor moves up you will have to muscle the rubber tube up. Or you can loosen the clamps on both ends, or the end on the riser, when the motor moves the rubber tube will stay in place, it's your call.

9- The flywheel will have to be switched and the coupler. That is where you may run into difficulties.

Post back at that point if you can't match it up, there may be a fix.
 
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Cant get the stern drive off. The steps in the book are:
1) disconnect the tilt cylenders - check
2) remove the 6 stop nuts - check
3) attach an] overhead hoist - check
4) carefully guide the stern drive unit straight back- uh uh. I've tried jarring it. smaking it with a rubber mallot, pound on it, jump on it. I can see where the gasket line is but it is still firmly mated. must be held on with super adhesive or a hidden bolt that's not in the docs.
Any suggestions?
 
You got the throttle in forward ? Hook back on the rams have someone else hit the up button and be ready to catch it cause it's going to come off fast.
 
No joy. Tried Bt's suggestion and chefalen's. It's stuck. My next attempt was to slide the engine forward. Motor mount bolts are seized. Even my air-drive wouldn;t do it.
 
Consider this, the splines of the shaft are rusted solid into the coupler. Or the gimbal bearing is rusted solid.

You put the throttle into forward ?????
 
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