My engine is siezed.

[Jbrookins]

So I have a mercruiser 120 and it won't move. I think water got in the engine I'm just not sure how. So now I have to rebuild the engine but if I can't figure out how water got in an I just going to end up with a broken engine again? So here's what I've done so far and what I've seen any advise would be greatly appreciated.

First of all last time I had the boat out it kept choking out when I gave it gas (5 months ago) so I brought it in and parked it in storage. And there it stayed until last week. Figured it was the carburetor so I took it off and it was bad. Ordered the rebuild kit and fixed it. The throttle body was stuck closed and had some surface rust on it(this is where I started to worry) I also noticed there was a lot of surface rust on the exhaust pipe and around where it connects to the engine. It was like that before the last time I took it out but couldn't find and water leaking so thought it just got wet at some point.
So when I reinstalled the carburetor I tried it start the boat and it wouldn't turn.
I removed the spark plugs and there was a little rust on the plugs(just a very little wondering if the plugs were not sealed.
I then sprayed some pb blaster in each cylinder and let it sit over night. The next morning still couldn't get it to turn so I decided it was time to remove the engine.
When I removed lower unit water poured out of the place where the gimble bearing is.(?)
Now I'm at the point where I guess I have to rebuild the engine but I'm not sure how to make sure I'm getting the right parts and what manual to use for all the torque specs and why all that water poured out of where the gimble bearing is. My motor has a stamp on the side of it that says serial number 6891754 and its a mercruiser 120

 

[wahlejim]

Sounds like there are a couple of things going on here:

1) Rust around exhaust manifold is concerning. If the whole passage is not air tight, water can leak back into the cylinders.

2) Water by the gimbal bearing is most likely a leaky u-joint bellow.

Pressure test the block before you sink any money into it. If you have a cracked block, no point in rebuilding.

Is this a new to you boat?

 

[Alumarine]

Now that the drive is off does the motor turn?

You will need Mercruiser Service Manual #10 to rebuild it.
Part no. 90-14693-1 I think.

 

[Jbrookins]

Marc c: Still won't move with the drive off
@wahlejim: wasn't thinking block because all the rust stains look like they run down from the top. And I've had the boat for about a year
I also found a mercruiser 120 boat motor near me for 300. He says it runs but doesn't have a starter I'm thinking about taking my starter over there and looking at it see if it spins and do a compression test if those both check out it might be worth getting it would be in better shape then mine is now. Even if I put it in and still rebuild mine I could just sell it later lol

 

[Jbrookins]

so im trying to find gaskets and this is being alot harder then i thought. i did get the other engine for 300 i figured it would be easier to work on then mine. and hey ive got extra parts now if needed lol. so when i search online for things like valve cover gasket, oil pan gasket and oil pump gasket..... i get alot of options but most things are listed with just a part number not the engine it goes to. how do i know is that part number goes with my engine. ivwe tried to find a parts catalog for my engine with no luck is there anywhere i can find the part numbers for my engine

 

[Alumarine]

For some of the gaskets try a 1963 chevy II with the 4 cylinder. Some of them will work (not the head gasket)

Sealed power has a complete gasket kit their no. NOF 260-1506M Engine Gasket Set

 

[johnmorgan]

Did you try turning your motor over with a wrench at the front harmonic balancer to see if it is seized.
Make sure your spark plugs are out. and is the oil milky.

 

[Bt Doctur]

you mention oil pump gasket, never heard of it
look for a metal tag just above the starter and post the numbers
Contrary to popular beliefe, NEVER USE A CRANK NOSE BOLT

 

[achris]

Mercruiserparts.com have a drilldown for your parts list.

 

[Jbrookins]

So I did get the new engine and I'm going to replace some gaskets just because some of the stuff on my old engine look better then the new one and it's out of the boat I've got new exhaust gaskets, timing cover gasket, valve cover gasket, water pump and thermostat housing gasket. I read somewhere that you had to loosen the oil pan to get the timing cover off but mine came off just fine? My question is, what of these gaskets do I need to use gasket sealer on?