Mercruiser 120 to 140 upgrade

[LC1979]

I'm new to this forum and I had a question about upgrading my motor. I have a 1984 Sea Sprite Mark1 17 footer with a Mercruiser 120 I/O. I recently bought it from a friend ($300) whom accidently set the motor on fire! Not good. Anyway, I found a good deal for a good running 1968 Mercruiser 140 for $200 complete. I was wondering if this would be a good upgrade for my boat. I have been looking to see if the motor will work with my current outboard (sorry, new to boating so not fully up on the proper names of parts) and found that the '84 and '86 Mercruisers have the same size of drive shaft inputs. So I am assuming they will work. I dont have serial numbers at this time.

Is there anything to worry about with the extra HP?

Thanks,

 

[bigbob_FTW]

Re: Mercruiser 120 to 140 upgrade

Sounds like a good deal. I'd like to make that upgrade myself. I'm keeping my eyes open for one now.

 

[Bondo]

Re: Mercruiser 120 to 140 upgrade

Ayuh,...

It'll work,.. Except the exhaust manifolds are different,+ the exhaust Outlets won't line up...

 

[Howard Sterndrive]

Re: Mercruiser 120 to 140 upgrade

1968 Mercruiser 140

are we sure that's not the 6 cylinder 230 cubic inch 140?

EDIT - sorry - never mind, I see the 6cyl 140HP was a few years earlier....1963/64

 

[chiefalen]

Re: Mercruiser 120 to 140 upgrade

The 140 is a 1968 ??

 

[LC1979]

Re: Mercruiser 120 to 140 upgrade

Sorry about that. It is a 1986 Mercruiser 140. 181ci. I went over the 140 today and noticed it had a 2 barrel Mercarb on it. I think I am going to stick with the 2 barrel Rochester I have on my 120.

 

[chiefalen]

Re: Mercruiser 120 to 140 upgrade

It's a straight change out. Everything on one will fit the other no problem.

Your gonna love that extra 20 hp at your beck and call. I know i did.

Good luck !

 

[LC1979]

Re: Mercruiser 120 to 140 upgrade

I swapped over some parts this weekend. The only thing that did not swap over smoothly was the carb. The '84 rochester carb off my 120 did not fit on my '86 Mercruiser 140. The 140 has a bigger base plate on the carb and the barrels are bigger than the 120's. (flame arrestor did not fit either)

Simple rebuild of the Mercarb that came with the 140 and I should be good to go.

It is also a tight squeeze for the wire that connects to the choke assembly. I am using the fuel line from my 120 (one from the 140 was mangled.) The Mercarb is a tad bit wider than the Rochester so that fuel line runs right next to the choke. I thought about trying to bend the fuel line but i don't want to risk cracking it.

 

[Howard Sterndrive]

Re: Mercruiser 120 to 140 upgrade

The only thing that did not swap over smoothly was the carb. The '84 rochester carb off my 120 did not fit on my '86 Mercruiser 140.

If the rochester carb was working well, I'd swap the whole manifold over.

 

[LC1979]

Re: Mercruiser 120 to 140 upgrade

Thanks for the suggestion Howard, but wouldn't the smaller barrels on the rochester have less air flow resulting in less HP? The carb rebuild is a fairly easy process. Plus the manifold on the 120 has 10X more rust inside it. Again restricting air flow.

 

[LC1979]

Re: Mercruiser 120 to 140 upgrade

My upgrade came to a screeching hault this weekend. I went ahead an took Howard's advice and went to swap the manifolds. I removed the manifold from the 140 and discovered a 8" long crack in the block. It was hiding behind the manifold. I though to myself, well I can fix that. Then decided to drain the oil to see if I could turn the motor upside down and check the crank and piston arms. I pulled the oil plug and out comes about a gallon of water! I was not too happy. I decided to turn the motor upside down and check the bottom end anyway. When I turned the motor upside down, out pored about 4 more cups of water form the open valves on two of the cylinders. This is a problem. I'm sure this might have to go to a different forum, but does anyone think it is worth pulling the motor apart to fix? All but one of the valves are covered with rust. The top side of the head is perfect and the bottom end of the motor looks clean.

 

[tiki]

Re: Mercruiser 120 to 140 upgrade

I guess that explains the $200 price tag for a complete engine!!!