3.0 and the older 120 hp whats the differance

[alilley]

my boat has a 3.0 in it right now that is getting water in the oil. i have found another "project boat" on craigs list and they claim that they can t get it running. i was wanting to know what the differance between my 3.0 140 hp and an older (painted blue) 120 hp mercruiser they appier to be very close any help here would be greatly appreacted

 

[zbnutcase]

Re: 3.0 and the older 120 hp whats the differance

They are very closely related. The 120 has smaller bore & stroke, and depending on the year of your 140, a different head port layout, which might prevent you from swapping manifolds. And NO Mercruiser was painted blue, red flag for me!

 

[daydreamer1252]

Re: 3.0 and the older 120 hp whats the differance

no MerCruiser was painted blue......I have been using parts from a 120 OMC and the parts.....that had original paint (oil pan and valve cover) were blue.....a pretty blue at that....looks like some swapping has been going on.........

 

[Fishermark]

Re: 3.0 and the older 120 hp whats the differance

what the differance between my 3.0 140 hp and an older (painted blue) 120 hp mercruiser

Not a lot of difference on paper... but a huge difference in performance. I have been in a boat that had a 3 liter which blew. A 120 was put in its place. It was a dog! BIG difference in performance. Keep looking for another 3 liter (140).

 

[alilley]

Re: 3.0 and the older 120 hp whats the differance

i will try to post pics of the 120 hp after looking into i noticed where it has been painted. you can see scratches ans places where black is coming through plus it does have mercruiser decals. i did noice to differant main things after looking at the phots again. 2 the manifold riser, mine is nice and rounded off could this be the differance in the age. 2 mine has all the shift linkage on top of the valve cover this one is not.

next question and this might involve a little reasearch and i would not have a clue where to start. if there is a differance between bore and stroke, is there a differance in the rod and main sizes. what i was thinking about doing (if they will fit) swaping my guts into this block. if i need to have it bored or have the mains bored slightly so be it

this is kind of off the wall but how do you get rid of a bad (at least bad to me) fiberglass hull what i am looking at is a complete boat but the interror is shot as there is nothing there. it does come with the trailer. i figure if i can get it for the right price and sell the trailer off i might be able to break even. what the thought there

 

[coheej]

Re: 3.0 and the older 120 hp whats the differance

Why don't you take yours apart and see what's wrong first? It's possible it could just be a head gasket. Also what's the year of your motor and of the one you're looking at?

 

[alilley]

Re: 3.0 and the older 120 hp whats the differance

 

[alilley]

Re: 3.0 and the older 120 hp whats the differance

this is the pic's they sent me of the 120 hp that i am looking at mine is a 1988 and i might be mistaken but i think the add said it was a 77 modle i am waiting on comfermation on that now. i have read that the odds of it being just a head gasked allowing water in the oil are slim. my block is cracked below the manifold as well. i did patch it with jb weld and all but i small piece held . i was thinking of fixing that but if i am getting water in the oil why? what are the odds of it being just a head gasket? if you read DON S post about water in the oil he mentions in there the odds of that being the case are very slim. i guess i will be taking the head off this weekend to see what is going on. are they the same as taking a v 8 pushrod/flat tappet head off?? does any one know where i might be able to d/l a service man. for this part of it?
many thanks again

 

[coheej]

Re: 3.0 and the older 120 hp whats the differance

You didn't mention the known crack in the outside of the block.
The only way your guts will fit into that block is if it can be bored .125" overbore. You would have to sonic check the block to know if the cylinder walls would be thick enough for that. In that old of a block I doubt that the walls are that think. The mains of your crank are most likely the same, but the rod journals are different, so you would have to keep your rods with your crank. The pistons from your setup would also have to be used because of the compression height of the pistons. I don't know if the heads would interchange.

 

[thumpar]

Re: 3.0 and the older 120 hp whats the differance

The 120 is a 2.5l. It can't be bored to a 3.0 piston size.

 

[coheej]

Re: 3.0 and the older 120 hp whats the differance

The 120 is a 2.5l. It can't be bored to a 3.0 piston size.

If it were a newer block, it could be. I've done it. a sonic check needs to be done to know for sure.

 

[alilley]

Re: 3.0 and the older 120 hp whats the differance

as far as the crack on the outside of the block i aint to concerned about that. my main concernis that i am getting water in the oil and at what i feel like is a pretty good amount. i will put this way i put fresh oil and filder on it and put less then 5 hours on the water. we took it out one day and noticed that it was not running up to par. first thing i did was lift the engine cover and noticed somthing spayed on the bottom that looked like cholate milk. checked the oil ans sure enough same thing but it was over full. i let it sit for the week went do and to do some looking around, pulled the dip stick and there was nothing on the bottom but about 1/8 inch up it had the cholate mike. my boy is small enough to where he can get under enough to pull the oil drain plug out drained it into a trash bag which i later put into a gas 2 gal gas can in which it came about 3 inched from filling. now i know 5 quarts (minus 1/2 a quart for filter)is oil but the rest would have to be water.

with it taking on that amount of water in that short amount of time what are the odds of it being a head gasket? as i stated before the block is cracked to the out side just below the manifold which i repaired most with j b wel and has held except for a small part. if i can figure out where i am getting water in the oil at i willpull out the oil j b weld and fix it again. not going to do that until i figure out the other issue first

on the 2.5 note i did do some digging around. my dad has a pontiac based 2.5 that has a bas rod in it with no head on it either. got to doing some checking and the as far as the main jernal sizes are concerned the 3.0 that i have will fit in it. they even run the same part number on the thrust bearing. not i do not know if i would have to clearance the block to fit the 3.6 stroke since the 2.5 runs a 3 in stroke. from what i have gatehr they both run a 4in bore but the next thing i have to look in to is connecting rod length and rist pin location . does any one have any insite on that ?? what are your thought on putting all my 3.0 stuff in that auto block??

 

[fishrdan]

Re: 3.0 and the older 120 hp whats the differance

I would keep looking for a 3.0 of your vintage. There are differences in the 120HP/2.5L, head, manifold, internals and the biggest,,, performance. The 140HP and 3.0L are basically the same, but also have differences, head, manifold, flywheel, coupler, etc, etc. You can't use an automotive block since the 3.0L/140HP was never used in cars & trucks, it's a marine/industrial engine.

I think the easiest and cheapest way to do this repair is to find another 3.0L.

As for scrapping a fiberglass hull, I took my old boat to the land fill and dumped it for $30-40,,, I had to have the title for it though......