exhaust manifold block off gasket

[brplut40]

I have had my boat for about a year and a half. Before I bought it, I test drove it and it ran great. The first time I took it out after I bought it, a cylinder was hydro locked. I have a Seakamp fresh water cooling system installed on my 4.3L GM Vortech V6, 262cid. It is in a 1993 Sea Ray 200 bow rider. The only part of the engine that is raw water cooled are the exhaust elbows. When the cylinder was hydro locked, it was because the block off gasket between the exhaust manifold and the elbow failed. We took our time and replaced the gasket and kept on boating. As time went on last year, you could tell the gasket was failing again because the engine was burning anti-freeze. It was always hard to start because anti-freeze would leak down into the cylinders, get the plugs wet, and make combustion very hard at the beginning. At the end of last year, I ripped it all apart again and replaced the gasket. I know I used a mercury replacement part both time, but cannot remember the exact part number. If I remember correctly part number 27-860231 replaced 27-41811, because the new part no longer required both the steel plate and the gasket. From what I read, the new parts that are gray, contain graphite, which is why you don't need the steel plate. At the beginning of this year everything ran great. As the year has gone on, I can tell the gasket is leaking again because it is hard to start and burns ant-freeze.

Does anyone have advice as to if I may be installing this gasket wrong or how to make the gaskets last longer than 2 months of use? It really sucks having less power and hard starts because of the anti-freeze in the cylinders. Not to mention, the extra wear on the engine. Any help is appreciated.

 

[Bt Doctur]

Re: exhaust manifold block off gasket

remove the risers, using a fine mill flat file, dress the riser surface and manifold surface, go back to the old ways, Permatex Aviation sealant, gasket, sealant, block-off plate, sealant, gasket, sealant, riser.

 

[brplut40]

Re: exhaust manifold block off gasket

Any idea where I might be able to get the old steel block off plate?

 

[Bt Doctur]

Re: exhaust manifold block off gasket

Bubba, the full kits include the exaust manifold in the system, the 1/2 kits only do the engine block.

Check shops that deal with" inboard engines
Mercruiser "Blue-Water " series

 

[brplut40]

Re: exhaust manifold block off gasket

Another question that may be stupid. I get the whole put the steel plate between 2 gasket thing. My question is why would you not put the steel plate directly on the exhaust manifold? Then the steel plate could take the 13 or so psi from the cooling system and the gasket would back the plate and ensure it does not leak. Right now the gaskets do not fully fail. It gets small tracks in it allowing the anti-freeze to seep down the manifold. I will take your word for it, but it seems like putting a steel plate between the gasket still leaves room for the gasket to slightly fail and seep anti-freeze into the cylinders.

 

[Bt Doctur]

Re: exhaust manifold block off gasket

First make sure the surfaces are flat using a fine mill file.
When you want to join two metal sections that cannot be milled indentical to provide a positive joint,a gasket must be used. How would you create a seal putting the block off plate directly on the manifold? The full metal block-off plate is solid with no water port slots so it dosent matter what riser gasket you decide to use.Just one on top and one on the bottom.
RWC motors use a gasket to seal the riser to the manifold and they dont leak water into the chamber or engine

 

[brplut40]

Re: exhaust manifold block off gasket

Then just to make sure I am thinking right. I will get 2 newer block off gaskets. Part number 27-41811 and put a steel plate part number 20-87918 between them. Should I use a gasket sealant/maker or not? Is it better to use gaskets that have openings or not?

 

[Bt Doctur]

Re: exhaust manifold block off gasket

Dosent matter on the gaskets, Make sure you get the SS block off plate
Permatex Aviation Sealant, most good auto stores have or can get it.
A new flat mill file (fine)
dress the manifold and riser surface
apply sealant to manifold, wait till slightly tacky,apply gasket
apply sealant to gasket, wait untill tacky, install block -off plate
apply sealant to block off plate, wait till tacky, install gasket,
apply sealant to gasket, wait untill tacky, install and tighten riser.

 

[brplut40]

Re: exhaust manifold block off gasket

I thought I had it fixed, but I am still having problems. I am testing to make sure that I didn't mis-diagnose the first time and it is not a blown head gasket. With that discussion aside, reading through the Osco, which is what my manifolds are, tech tips, it states not to use any sealers, silicon, or compounds. It goes on to state that this may lead to pre-mature failure. The last time I put things together I took Bt Doctur's advice, but could not find Aviation Sealant, so I used permatex high-temp red RTV silicone gasket maker. So for round 4 I am thinking of using no sealant, Osco 8503-GB, and a stainless steel block off plate between 2 gaskets. Was there anything that I did wrong last time?

 

[Bt Doctur]

Re: exhaust manifold block off gasket

Permetex #2, Aviation sealant, shellack, Indian Head Sealant,
ANYTHING BUT SILICONE

 

[JJJ]

Re: exhaust manifold block off gasket

Hi, I am having the same issue but with Merc manifolds and risers.

IS that part # for the blockoff plate the correct # for the SS version???

I questioned not using a blockoff plate and just that gasket from the beginning!

I'm hoping the leak is there and not a cracked head/intake manifold, only using enough to be able to smell antifreeze on startup and not building any pressure in the cooling system.
It is getting worse though and I'm hoping it makes it through next week - will repair it when I get back home.

 

[brplut40]

Re: exhaust manifold block off gasket

The mercrusier part number for the block off gasket is 27-863725 1 This part number replaced both 27-41811 and 27-860231, I verified this with Mercury today. The new part number no longer requires a stainless steel plate. The new gaskets have graphite in them, but I don't know how much I trust them.

Part number 8503-GB is the Osco block off gasket and 8503-SS is the Osco stainless steel plate. I am still wondering if you can just use a single gasket, either 27-863725 1 or 8503-GB and that will work.

JJJ did you just use a single gasket, or 2 gaskets with a stainless steel plate in the middle?

I guess the question now is who has experience with using a single gasket vs. 2 gaskets with a stainless steel plate?

 

[Bt Doctur]

Re: exhaust manifold block off gasket

Think of it this way,
you use a gasket to seal a manifold to riser joint, you use 2 gaskets when using a riser extention. Why?, because the manifold, riser block, or riser was not machined to go together by themselves without some type of gasket to seal everything.For years, a SS blockoff plate was used to seal the manifold from the riser with closed cooling and used a gasket above and below the plate.Merc decided to save a few pennies and devise a gasket without any re-inforcement. If they fail ,your AF goes right out the exaust.
Use a gasket above and below and you wont be having any issues.The gasket below the plate seals the manifold off and the one above seals the riser off.
AND NO SILICONE

 

[JJJ]

Re: exhaust manifold block off gasket

I used the NEW graphite gasket, and of course they almost all have a small wrinkle/imperfection in them by the time they hit the manifold.

I will go to the Osco parts.

IMO mine has to be that gasket, intake manifold (or gasket), or cracked head but past the valve (not in the combustion chamber).

The boat is out of state, so when I get back to it (this sat.), I will drain a bit of the oil and see if there is any water/antifreeze in the oil - none of dipstick OR in the oil fill area. I also only smell it on startup, after that I no longer smell antifreeze.