Rebuilding a 120hp Force, costs, etc...

[racer-x]

Hello all.

I have a 120 hp motor, I think that it is a 1995 model. It is obviously Force, but has Mercury Marine on the engine cover as well.
It is much larger when compared to an older 120 Force, why I have no idea.

I have a bad cylinder, (about 5 psi) and 3 at 140 or so. I have no idea why it has such poor compression.... but the motor still runs. It only pushes the boat at about 5 mph now.

What are the costs of having the powerhead torn down and rebuilt?

Any suggestions as to why the one cylinder had sudden low compression but the engine still runs?

 

[Frank Acampora]

Re: Rebuilding a 120hp Force, costs, etc...

Most likely you had a lean run, melted the piston, and/or broke the rings. The engine will typically start and run on three cylinders, but the loss of power plus the extra drag of the dead piston will severly limit horsepower and speed. The more you run it, the worse the damage will get until the cylinder liner is so badly scored that it must be replaced rather than rebored and the worn metal may get into bearings, ruining them and the crankshaft, thus making it not economical to rebuild yourself.

You really don't want to have a mechanic redo the engine since they are going to charge you 100 bucks an hour plus usually they buy a rebuilt block for 1200 bucks. So, you would be looking at anywhere from 1600 to 2500 bucks. PLUS: it is the height of the season now; you will probably wait at least a few weeks for him to get to it.

Teardown and reassembly is not too difficult and if you are at all mechanically inclined, you can do the job yourself. A new piston from Wiseco is about 125 and a rebore oversized is about 65 bucks. You really only need to redo the bad piston and cylinder but if you are doing it yourself, The money you save can go into reboring all four cylinders and buying four oversized pistons. Then, you have an almost new engine. Total time would be about ten hours or a little more since you have never done it before, without the waiting for parts and reboring.

If you feel you are not up to the task, you would be better off finding a fellow like me in your area who rebuilds on the side as a hobby. For example, I charge 500 plus parts for a complete Force rebuild and only do a couple a year by word of mouth. If you ask around, you should be able to find someone. Ask at the local bass club. Those guys are rough on engines and typically get a lot of repair work done.

 

[baxtr]

Re: Rebuilding a 120hp Force, costs, etc...

Ditto on Franks Post, My 125 lost a piston a few years ago now, shop didn't even want to touch it due to it being an older force, one of the techs said he would do the one piston as a side job for 1500 bucks . I decided to do it myself, never having done it before, but figured what could I lose. I replaced 2 pistons, had it over bored, re honed all cylinders, all new gaskets, new exhuast plate, all for 600 bucks and a weekend of my time. Very easy, even for a novice, just take your time and a lot of pictures.

 

[racer-x]

Re: Rebuilding a 120hp Force, costs, etc...

Wow thanks.... I hear over and over that Force are generally easy to work on!