Re-Power a Mercruiser Run-About

My old boat has a Mercruiser 120 which I have discovered is not going to run. The boat sat around for years and it is too long and boring a story to explain why. Low compression in 3 of 4 cylinders. Possible freeze damage IMO.

I want to Re-Power, but the 120 block is no longer manufactured and hard to find used.

So I have these choices for repower:

1) Replace the entire drivetrain with a 3.0 or 4.3 Mercruiser set-up (Engine, Stern bracket and outdrive). I say all three items because I was told today by a marine repair facility that my 120 engine accessories are not compatible with the 3.0 Mercruiser.

2) Hang an out-board bracket on the stern and buy an outboard set-up

3) Find a re-buildable GM 2.5 liter (Mercruiser 120) and re-build. Near impossible it seems.

If you have done any of these options to your boat or are a marine mechanic, what should I have to pay for these options?

Thanks for opinions in advance!

Buy a 3 liter replacement engine.

Jeff

3.0 is essentially drop in. What year is the original? Would think some of your original components would swap over. 3.0 changed to single piece rear main seal in 1990 flywheel sized changed to accommodate it.

if your boat is larger you may want to consider the more involved 4.3 swap for more power.

best way is to find a beat up boat or a complete take out pulleys to prop to swap in.

Maybe just shop a newer boat....

Docksidemarineservices said:

Maybe just shop a newer boat....

Click to expand...

Unless the boat is "special" or a particularly good make/model, the best advice....

I think I will ask some other local marine repairs about swapping in a 3.0. The one I asked already said everything had to change. Maybe they are correct and maybe not. I won't be foolish and dump too much money into this one.

I found a rebuilt (early model) 140 that accepts all my accessries. I'm in the process of installing it.