120 merc exhaust manifold leak

[swandogg]

Put the muffs on it today and found that the manifold is leaking water from where the manifold meets the block.
So after looking around online I find a couple different replacement manifolds. Now I don't know for sure if its the gasket or manifold but since it is coming off I am going to replace it anyway as I think I remember hearing 9-10 years you get from them. This correct? This is the original. Plus after taking out the plug to drain the water I find that it is stripped when trying to put it back in.
Now what else as far as gaskets am I going to need or what else should I replace while I am in there? May pick up a carb rebuild kit as well to solve a different problem.
Also are these the same manifolds as the gaskets look different to me. If its any consequence I have the merc carb. Any other good sites to shop at? Many thanks.

http://www.iboats.com/Exhaust-Manif...3210561--**********.460575703--view_id.222305

http://bpi.ebasicpower.com/mm5/merc...roduct_Code=BARMC-1-99798&Category_Code=MER9A

 

[cedarjunki]

Re: 120 merc exhaust manifold leak

Put the muffs on it today and found that the manifold is leaking water from where the manifold meets the block.
So after looking around online I find a couple different replacement manifolds. Now I don't know for sure if its the gasket or manifold but since it is coming off I am going to replace it anyway as I think I remember hearing 9-10 years you get from them. This correct? This is the original. Plus after taking out the plug to drain the water I find that it is stripped when trying to put it back in.
Now what else as far as gaskets am I going to need or what else should I replace while I am in there? May pick up a carb rebuild kit as well to solve a different problem.
Also are these the same manifolds as the gaskets look different to me. If its any consequence I have the merc carb. Any other good sites to shop at? Many thanks.

http://www.iboats.com/Exhaust-Manif...3210561--**********.460575703--view_id.222305

http://bpi.ebasicpower.com/mm5/merc...roduct_Code=BARMC-1-99798&Category_Code=MER9A

what year??
well to answer the ? how long do they last....im running what looks to be original on my 1969 120. just replaced the original manifold 5 years ago on my fathers 1970 140. i would do a tear down first before buying parts! may be just a gasket, or worse cracked head/block...
stripped plug threads is a very simple easy fix! and alot cheaper.

 

[Bondo]

Re: 120 merc exhaust manifold leak

Now I don't know for sure if its the gasket or manifold but since it is coming off I am going to replace it anyway

Ayuh,.. There's No water present at that gasket,...

Sounds like the block, head or manifold Froze...

 

[cedarjunki]

Re: 120 merc exhaust manifold leak

Ayuh,.. There's No water present at that gasket,...

Sounds like the block, head or manifold Froze...

now i feel dumb! i didnt catch that..... way too long of a day at work today!

 

[swandogg]

Re: 120 merc exhaust manifold leak

Ayuh,.. There's No water present at that gasket,...

Sounds like the block, head or manifold Froze...

This leak started the last time I was out with it last year. Just now getting around to fixing it. So it didn't freeze. Plus it stays in my comfy 65 degree garage every winter.
When looking at the engine it is leaking right in the middle of the manifold up underneath where I can't see. That's why I figured it was around that gasket. I got out an inspection mirror and a flashlight but that didn't show me anything. Now to tear it down.
I had searched the threads here for info and that is where I got that they last 10 years or so at.
I'll be having a friend help me take it apart since he is more familiar with boats than I am. Plus it was his at one time.

 

[Bt Doctur]

Re: 120 merc exhaust manifold leak

2 core plugs are listed,and there is also a 3/8ths pipe plug in the head. Have to atleast pull the manifold off and look at the head.

 

[cedarjunki]

Re: 120 merc exhaust manifold leak

This leak started the last time I was out with it last year. Just now getting around to fixing it.

is there sign of water in the oil? just slightly milky? or overfilling and milky?
if it started when you were using it, i would suspect either the manifold or the riser along with a bad manifold gasket.

 

[swandogg]

Re: 120 merc exhaust manifold leak

is there sign of water in the oil? just slightly milky? or overfilling and milky?
if it started when you were using it, i would suspect either the manifold or the riser along with a bad manifold gasket.

No water in the oil thankfully. Very clean too.

 

[bigskiohio]

Re: 120 merc exhaust manifold leak

mine is a 73 and is rusted and leaking a littl out of the bottom thru rust but my studs look severley rusted so i am waiting till it really needs it as it only drips while running and my bilge pump takes care of it.

 

[swandogg]

Re: 120 merc exhaust manifold leak

Finally I was able to work on it today and found a crack in the block just below the head.
Thanks again for the help. Here are some pics of the crack for someones future reference.
Not sure what I can do at this point. Obviously someone before me didn't winterize it at some point and it finally cracked all the way thru.
How expensive will a replacement and all the extras run me that I will need? And where should I be looking at for a replacement?

 

[Bt Doctur]

Re: 120 merc exhaust manifold leak

Looks like the garage wasnt warm enough.

 

[swandogg]

Re: 120 merc exhaust manifold leak

My garage is set to 60 in the winter. I have thousands worth of detailing products that I would lose if they separated. That would hurt me more.
I think this may have cracked a while ago and finally opened up to start spewing water. Trust me, it goes in the garage before it gets cold out and it gets drained. The leak started at the end of summer last year.

After searching the site I see where others were successful in repairing with JB Weld. I picked some up along with some wire brush attachments and have sanded it all down. Put a v-groove in the crack and am just about to fill it. I'll take some more pics along the way. Oh and going to drill some holes also at the end of the crack.
For $15 in materials it is worth a shot to fix since it is only a water leak and no water in oil so I got lucky sort of.
Going to replace the gaskets also so hopefully I can get them soon and test it out.

 

[cedarjunki]

Re: 120 merc exhaust manifold leak

clean out the crack and area with acetone or thinner or something first.
then take a torch and burn off the residue left over.

use the original liquid jb too.

cant wait till the guys read cracked block and jb-weld
it is fixable!

personally i would try! and i know many others have! i just wouldnt trust it too far.

 

[swandogg]

Re: 120 merc exhaust manifold leak

I read on here to do 2-3 coats of jb-weld. Now that I have one applied, I am going to do another today. I believe I would get better adhesion by sanding in between coats correct? Or does that weaken the weld?

Finding new gaskets is proving harder than fixing the crack. Mercruiser carb gasket that is on there doesn't look anything like I am finding online.

 

[cedarjunki]

Re: 120 merc exhaust manifold leak

I read on here to do 2-3 coats of jb-weld. Now that I have one applied, I am going to do another today. I believe I would get better adhesion by sanding in between coats correct? Or does that weaken the weld?

Finding new gaskets is proving harder than fixing the crack. Mercruiser carb gasket that is on there doesn't look anything like I am finding online.

yes sand it so it has something to bite. and extend the next layer farther than the first. if you want a little extra strength use a piece of window screen in the jb as well.

is it a merc carb or rochester? what year? or serial number?

 

[swandogg]

Re: 120 merc exhaust manifold leak

yes sand it so it has something to bite. and extend the next layer farther than the first. if you want a little extra strength use a piece of window screen in the jb as well.

is it a merc carb or rochester? what year? or serial number?

I ended up finding it today at the third local dealer I tried. Between two of them I got all the new gaskets I need.

 

[swandogg]

Re: 120 merc exhaust manifold leak

All back together and holding strong. Had it on the muffs for 15-20 mins. I still have a leak from the drain plug on the manifold. About a drop every 10 seconds. I used a tap to clean it up and am going to have to get a new plug as the old one is stripped. Those should be brass correct?
Also the riser gasket that I replaced is leaking. Tore it apart a few times and still leaks. Guess I'll put some gasket sealant in there tomorrow when I take it off again and hopefully that takes care of it.
Otherwise everything else went good thanks to this forum and the service manual I downloaded from here.