3.7 Head Gasket??

[Live-liner]

Good Morning all,

Just looking for a bit of input.
I just replaced the head gasket on my 1986 3.7 190. This is what the deck looked like upon disassembly. My compression test came out as; #1-155, #2-150, #3-125, and #4-135. Couldn't get the boat to idle and saw some steam and loss of coolant, hydro-lock (hard starting), etc. Prompted me to replace manifold and elbow. Put it all back together and still had issues, took head off and replaced head gasket.
This is what the srface looked like, note the dark areas around the front of #3 and #4, also dark areas on the sleeves of both cylinders, also lots of crud on piston #4. Can I assume that there was definately a leak in those areas? I did clean everything up befor re-assembly. ad cleaned the head and valve surfaces where there was actually light rust (no carbon)
There was no etching or anything on the surfaces, everything cleaned up nice. I will finish getting it back together this weekend and retorque the head after warm up.

Thank you in advance for your input. I have been dealing with the issues associated with this motor for the last three years before stumbling upon this forum. I wish I would have looked it up earlier!

 

[nola mike]

Re: 3.7 Head Gasket??

IDK that you could definitely assume a HG leak by looking at that block. What did the gasket look like? Symptoms certainly sound more like a mani/riser issue.

 

[Live-liner]

Re: 3.7 Head Gasket??

Gasket was difficult to read. It was kinda bent and screwed up by the time it came off. Manifold/riser was deffinately the original issue, but problem still persisted after replacing, and a shakedown run. At that point, I replaced head gasket because the compression test seemed to point to a leak between #3 and#4 (I could be wrong, but it was a worthy maintenance)

 

[Another retired guy]

Re: 3.7 Head Gasket??

Gasket was difficult to read. It was kinda bent and screwed up by the time it came off. Manifold/riser was deffinately the original issue, but problem still persisted after replacing, and a shakedown run. At that point, I replaced head gasket because the compression test seemed to point to a leak between #3 and#4 (I could be wrong, but it was a worthy maintenance)

Are you saying that ALL of the problems listed persisted after the manifold/riser replacement?
It sure looks like #4 was leaking.

 

[Live-liner]

Re: 3.7 Head Gasket??

Yes Sir, that's what I'm saying. Symptoms improved tremendously, but still existed. I assumed that maybe the head gasket was blown, or the manifold or elbow gasket wasn't seated properly. So I replaced head gasket and am about to re-assemble exhaust side with new gaskets (OEM). I will perform a new copression test once assembled. I was curious if the marks on the deck indicated a bad head gasket seal.

 

[Another retired guy]

Re: 3.7 Head Gasket??

Yes Sir, that's what I'm saying. Symptoms improved tremendously, but still existed. I assumed that maybe the head gasket was blown, or the manifold or elbow gasket wasn't seated properly. So I replaced head gasket and am about to re-assemble exhaust side with new gaskets (OEM). I will perform a new copression test once assembled. I was curious if the marks on the deck indicated a bad head gasket seal.

Well, those black marks on the block by #4 sure look like a leak between the cylinder and water passages! Hopefully the new head gasket will solve your problems.

 

[Live-liner]

Re: 3.7 Head Gasket??

Thank you, I'm hoping so.
One more question..... Should RTV be used on the exhaust manifold to head and manifold to riser gaskets? Manual says not to use anything on the head gasket, use perfect seal on the intake gasket, but does not mention the exhaust side. Typically I would put a thin coat on anything water-side. I did use it last time, (of course last time failed) but wanted to make sure this time.

 

[Another retired guy]

Re: 3.7 Head Gasket??

I have no experience with RTV but I just did a quick search on RTV uses, and I read many comments saying do NOT use it on exhaust manifold. Exhaust temps are too high.

 

[Live-liner]

Re: 3.7 Head Gasket??

Ok, so what (if anything) should be used on the exhaust to head? Copper sealant?
Hwow about between the manifold and riser?
I just don't want to cause myself an issue.......

 

[sti1471]

Re: 3.7 Head Gasket??

Before you put the head back on, take a straight edge and a feeler gauge and check the gaps on the entire head surface, and block surface. nothing more than a .006 feeler gauge should slide between the surface and straight edge. If you are over .006, then you need to flatten your surface or you will be replacing the head gasket every few weeks.

If you are sliding .007+ between the surface and straight edge, it means that your gaps are too large and the head gasket is not sealing around that area. If you installed a new gasket and it improved but was still there, I am guessing you have a low spot somewhere on one of the surfaces. You need to make sure both levels are flat with .006 preferably .002-.004 feeler.

After looking at the picture, can you tell me what these are? If they are carbon buildups then the head gasket is not going to seal around these. If you run your fingernail over any of these black spots and feel anything other than smooth like glass, these need to be removed 100%. from the looks they are all kind of concerning, but especially the black all around the cylinder lip of #4.




The only thing that should be used between the head and the exhaust manifold is a new gasket. If your exhaust manifold gasket surface is flat and level, then you will not need anything more. If you are needing to use gel gaskets to fill gaps, you are only trying to slap lipstick on a pig as there is something else that need to be addressed.

Try the straight edge and feeler gauge on both the exhaust manifold surfaces as well to ensure there are no high or low spots.

[edit] looking at your picture, there are a few spots on this surface that looks warped. what are these?

 

[Another retired guy]

Re: 3.7 Head Gasket??

Ok, so what (if anything) should be used on the exhaust to head? Copper sealant?
Hwow about between the manifold and riser?
I just don't want to cause myself an issue.......

Anything I've read says do not use any sealant on exhaust manifolds or risers. Install them dry - that's what the gasket is for. As sti1471 has said, just make sure surfaces are level. IMHO sealants are a "quick fix" for uneven mating surfaces, and will not last long

 

[Live-liner]

Re: 3.7 Head Gasket??

Thank you,
I just want to let you know that I appreciate your input, and I certainly wasn't looking for any quick fix. I just wanted to know if any sealer was recommended. I took my time and cleaned all the surfaces and checked with a straight edge (head and block) everything looked to be within tolerance. The black carbon build up around #4 cleaned up with a little gasket remover and back blading with a razor blade. I may have caused myself issues by originally putting red RTV on both sides of the manifold and riser gaskets 1st time installed????
Sti1471, The spots you see on the intake manifold were light corosion and gasket material that hadn't been cleaned off yet. The shiny spot to the left was one area I cleaned with razor blade before picture was taken. I did put perfect seal on both sides of that gasket and bolt threads before installing (as per Merc manual #8)
I hope to install exhaust side today and perform a second compression test. I think I should also do a pressure test on the manifold and riser. Any instructions or how to's on that proceedure?
Thanks again!

 

[Another retired guy]

Re: 3.7 Head Gasket??

Re your question on pressure test - you may get more replies if you start a new thread specifically asking that question. Folk have probably stopped following this thread

 

[sti1471]

Re: 3.7 Head Gasket??

Here is a good write up on how to pressure test your exhaust manifold without an air compressor. it was written by Don S. so you know it works!

http://forums.iboats.com/mercruiser...s/testing-exhaust-manifolds-leaks-288629.html

 

[sti1471]

Re: 3.7 Head Gasket??

"I did put perfect seal on both sides of that gasket and bolt threads before installing"

I do not think that perfect seal is to be applied to the gasket itself but only the threads of the bolts. I might be wrong though, but I have never heard of a head gasket that needs to have perfect seal applied on the main gasket for a good seal. To me that is scary as this just creates more crap that can melt, come loose and get in the valves, cylinders, and rings and mess stuff up. perfect seal only stands up to 400F, so if it gets hotter than that on/in the head surface, that stuff is melting and trust me you don't want to know where it's running to.

make sure when you checked the surface areas on the block, that you made all 9 point checks shown in this picture I created for you. Start from the tip of the engine on one side, and slide the feeler gauge along the block against the straight edge. When I did mine, I notice at points, there was a space that was 1" or so that the feeler gauge would slip under the straight edge and it showed me the low spots.



Also inspect the head and block surface for gouges or hair width surface cracks that gases and liquids use to travel under or above the gasket. My head had 1-2 of those as well.