5.7 Mercruiser Riser Replacement Questions - Fresh Water Cooled

Hey Team,

I looked through threads and couldn't really find what I wanted. Boat is a 1989 Sea Ray Sundancer, engine is a 5.7 mercruiser carbed engine. Its a replacement engine as of 2009, but I assume it is a rebuilt version of the same 1989 motor. I have a closed cooling system (freshwater cooled, or whatever you say for cooling that has an antifreeze system). I know enough to know that my risers are raw water cooled while my manifolds are freshwater/antifreeze cooled. I want to buy parts before I take it apart, just because I don't want it to be sitting in the water with the risers off and raw water hoses out for any longer than it has to.

So my question is, do I need a solid stainless steel blockoff plate with this? If the engine was new 7 years ago, I assume that is realistically the last time risers were replaced. It has probably 200 hours on the new engine, virtually all salt. I want to change the risers just so I know I'm starting on a clean slate with it. I bought it last year. My question, when I'm buying parts, is do I need a stainless steel block-off plate between the risers and the manifold or will a gasket do here. It doesn't seem like there are many stainless blockoff plates available, which leads me to believe that many people just used some kind of gasket to do the blocking the the past. Intuitively that doesn't seem sufficient to me and I assume I need a blockoff plate (with a total of 2 gaskets per riser). Is this right? It doesn't look like there's a blockoff plate sandwiched in there now, but its difficult to tell. Am I missing something here? Is there always a metal blockoff plate in a freshwater cooled system or do people just use some kind of reinforced gasket in there?

Also, do I add any RTF type sealant or just do this installation dry? Does the bolt grade matter like it does on heads?

Thanks,
Stang

Stick with the OEM stainless (solid) gasket/blocking plate. Based on year, I assume that these elbows are the dry joint/ceramic types. The OEM gasket blocking plate is a sandwich of a SS blocking plate with graphite impregnated gaskets laminated to them. Additionally, that plate has an UP and a DOWN when installed, as it is not flat and has a trapizoidal funnel shape formed into it. This "feature" is called a turbulator. Proper installation is a must to reduce rust in the exhaust ports from condensation. Given your investment in this engine, I would also replace the bolts with MERC OEM bolts. They aren't exactly the kind pf bolt you'll find at your local hardware store. What you will find, as I did much to my annoyance, is that there are two threaded ports in each elbow. The one you use is dependent on your exact installation. The elbows come with a brass plug to close off the unused one. There are two gotchas that can tie you up unexpectedly (if you don't do this for a living)

1) The brass plug is an allen, and a large one at that. Larger than any size that comes in a standard allen set. I made my own driver with a bolt and two nuts, wherein the bolt head became the allen drive and the nuts were driven by a standard socket wrench.

2) The above mentioned threads in the tapped holes in the elbows aren't protected by either a CAPLUG or even masking tape at the factory and are therefore filled with the same baked on very tough paint that the rest of the elbow is covered with. Beg, borrow or steal the correct size tap to "chase" these holes clear of paint, otherwise, neither the brass plug nor the water hose fitting will correctly install. Cleaning out these tapped holes by any means other than a tap takes HOURS.... trust me! This correct size tap is NOT a Sears or Harbor Freight item as a stand alone... at least in my neighborhood.

TIP... cut the heads off of two of your old bolts and loose thread them into two holes in the manifold diagonally to make guide pins to help install/align the elbows correctly. Things will go easier if you do.


ENTER the serial number of you engine into the parts search engine on this website parts section to find the correct parts for this... to reiterate... two blocking gaskets, 8 bolts in addition to the OEM elbows.... MERC OEM!!!

Before you remove anything DRAIN the manifolds first BEFORE you remove the riser,
Are these standard manifolds and risers or dry joint manifolds and risers
If standard ones, keep the SS plate and use 2 regular gaskets above and below the plate

Bt Doctur said:

Before you remove anything DRAIN the manifolds first BEFORE you remove the riser,
Are these standard manifolds and risers or dry joint manifolds and risers
If standard ones, keep the SS plate and use 2 regular gaskets above and below the plate

Click to expand...

It's a standard riser. Do I just drain the manifold to keep antifreeze from draining over the top and down into the cylinders? With freshwater cooling do I for sure already have a stainless plate in there? Should I reuse the existing if one of it is there? Should the new gaskets be dry or with sealant applied?

these are standard kind of gaskets right, without the Ayer channels?

thanks for the tips all

It's a standard riser. Do I just drain the manifold to keep antifreeze from draining over the top and down into the cylinders?

Yes

freshwater cooling do I for sure already have a stainless plate in there

Maybe, it could be just a block off gasket or a SS plate with a regular gasket above and below it.

Should the new gaskets be dry or with sealant applied?

I use Permatex Aviation liquid, has never let me down.

It's a standard riser. Do I just drain the manifold to keep antifreeze from draining over the top and down into the cylinders?

Yes

freshwater cooling do I for sure already have a stainless plate in there

Maybe, it could be just a block off gasket or a SS plate with a regular gasket above and below it.

Should the new gaskets be dry or with sealant applied?

I use Permatex Aviation liquid, has never let me down.
http://www.marineengine.com/parts/m...anifold-and-exhaust-elbow-cast-iron-exh-elbow

Curious... Merc changed to "Dry Joint" technology in 2002... Dry joint refers to a design wherein water flow to the elbows via separate cast paths rather than along side the exhaust port itself. Dry Joint elbows have a "footprint" on the exhaust manifold of a rectangle with "ears"... instead of just a rectangle.

.............................

luvmystang67 said:

Hey Team,

I looked through threads and couldn't really find what I wanted. Boat is a 1989 Sea Ray Sundancer, engine is a 5.7 mercruiser carbed engine. Its a replacement engine as of 2009, but I assume it is a rebuilt version of the same 1989 motor. I have a closed cooling system (freshwater cooled, or whatever you say for cooling that has an antifreeze system).
This would be technically known as a Closed Cooling System.

I know enough to know that my risers are raw water cooled while my manifolds are freshwater/antifreeze cooled.
I believe that you mean that your Elbows are RWC.
Spacers/Risers separate the exhaust manifold from the elbow. Spacers/Risers are typically ported as to allow for different combinations of plumbing.
Not all systems require Spacers/Risers.

I want to buy parts before I take it apart, just because I don't want it to be sitting in the water with the risers off and raw water hoses out for any longer than it has to.
I would agree with you.

So my question is, do I need a solid stainless steel blockoff plate with this?
Yes..... block-offs and the correct gaskets on either side, or a SS clad gasket.

Whether Full or Half system, Elbows are always RWC.
With a Full System (such as what you have), there is a need to prevent the E/G from entering the Elbows.

If the engine was new 7 years ago, I assume that is realistically the last time risers were replaced. It has probably 200 hours on the new engine, virtually all salt. I want to change the risers just so I know I'm starting on a clean slate with it. I bought it last year.

My question, when I'm buying parts, is do I need a stainless steel block-off plate between the risers and the manifold or will a gasket do here.
See above.

It doesn't seem like there are many stainless blockoff plates available, which leads me to believe that many people just used some kind of gasket to do the blocking the the past. Intuitively that doesn't seem sufficient to me and I assume I need a blockoff plate (with a total of 2 gaskets per riser). Is this right? It doesn't look like there's a blockoff plate sandwiched in there now, but its difficult to tell.
If there was not a gasket (or SS clad gasket) in between the two, your E/G would leave the system via the Elbow's mixing chamber.


Am I missing something here? Is there always a metal blockoff plate in a Closed Cooling system or do people just use some kind of reinforced gasket in there?
See your OEM parts breakdown.

Also, do I add any RTF type sealant or just do this installation dry?
It depends on the manufacturer...... some call for a sealant..... some are to be installed without.

Does the bolt grade matter like it does on heads?
A grade #8 fastener is less likely to break upon a stubborn disassembly down the road.
If the female threads are dead-ended, you should be able to use automotive Anti-Seize.

Click to expand...

Here is an example of Manifold, Spacer/Riser and Elbow.

RicardoMarine said:

Here is an example of Manifold, Spacer/Riser and Elbow.


View attachment 14683

Click to expand...

The above is an Aftermarket Non Dry Joint, i.e. typical of pre 2002 MERCs and most current aftermarkets... Below are OEM MERC "Dry Joint" ( as pulled and new)... note the "outrigger" water passages. Also pix of DIY allen hex driver and typical brass plug to be driven.

Bob, the OP says;

1989 Sea Ray Sundancer, engine is a 5.7 mercruiser carbed engine. Its a replacement engine as of 2009, but I assume it is a rebuilt version of the same 1989 motor.

Click to expand...

If he stayed with the 1989 OEM designed exhaust system, it would be Pre- "dry joint"...... Yes/No???

BTW, since there appeared to be some confusion re; Spacer/Riser -vs- Elbow, the image that I posted was to be an Example Only.
He more than likely has a center-riser style system (unlike what I showed us).



.

RicardoMarine said:

Bob, the OP says;


If he stayed with the 1989 OEM designed exhaust system, it would be Pre- "dry joint"...... Yes/No???

BTW, since there appeared to be some confusion re; Spacer/Riser -vs- Elbow, the image that I posted was to be an Example Only.
He more than likely has a center-riser style system (unlike what I showed us).



.

Click to expand...

Rick... If he stayed with 89 system, then, yes would be non dry joint. Given the ambiguity of "replaced in 1989", I was just concerned that he had dry joint and dry stack confused. I've had customers at my local "big box" store get them confused.

Hey, I didn't realize I didn't get emails anymore when replies were made to the post.

I most certainly have the pre-dry joint design. ie. its not a modern dry joint, but rather the old standard style elbow. Thanks for the riser versus elbow lesson, I'm certainly replacing the elbows, not risers as I don't have risers on this particular configuration.

Does anyone have an example of a part number that would be a good stainless blockoff plate? I see a bunch of examples of ones online and really don't know which would be the best. My current elbows are the Sierra 18-1976-1 , which for discussion's sake is listed as "Manifold Riser" not elbow on the site I'm looking at.

It recommends this gasket http://www.marineengineparts.com/sierra-marine-18-0672-exhaust-elbow-gasket.html, but doesn't show any kind of stainless plate. Do I just pick up 2 of these gaskets and assume I have a stainless plate already in-place in my stack-up?

Thanks,
Stang

http://www.marineengine.com/parts/m...anifold-and-exhaust-elbow-cast-iron-exh-elbow

Shows Item #10 as the gasket for FWC systems for your vintage engine. No other plate req'd. I should warn you that once you get it apart, the most teduious job is getting the gasket surface on the manifold CLEAN. Gasket should go down with Permatex per BTdoc's post. Clear the threaded holes for the water feeds, some mfgs do not mask this hole before painting...

MC-20-87918 - Block Off Plate, SS Barr Product
with a standard gasket above and below . Permatex Aviation wont hurt either

Is this part the stainless steel component only, with me needing 2 gaskets for each side of it, or does this part have gasket material on both sides? This is kind of where i'm hung up.

luvmystang67 said:

Is this part the stainless steel component only, with me needing 2 gaskets for each side of it, or does this part have gasket material on both sides? This is kind of where i'm hung up.

Click to expand...

No this P/N is just a thin S/S plate and requires a gasket each side.

Per the MC description..."MC-20-87918 Direct replacement stainless steel block off plate for use with MerCruiser riser numbers 98502, 98504 and 44354. Requires (2) gaskets part # MC47-27-41813"

What adds to the confusion is that a somewhat similar gasket for the dry joint elbow system is a thin S/S plate with gasket material laminated to each side of the plate and requires no other gaskets.

Okay, I've got everything. I've got 2 block off stainless steel plates, 4 block-off gaskets, 2 sierra elbows. The elbows are machine finished on the mating surface, but are also painted. Do I need to sand or file off the paint on the machine finished surface? Also, I know I already asked this, but I'm kind of planning on replacing these dry (without some kind of silicone). Do you really think I need some kind of goo on this application?

1) Do I need to get the paint off the machine surface, if so, whats the best way to do this without nicking the surface?
2) If I need to add goo, which type/color? Do i really need this? The gaskets seem a little gooey already... I don't want to overgoo anything.

Thanks

Personally I would use a fine cut flat file to be sure the surface is flat.Just a light touch is fine.
If you have the mercruiser gaskets there like graphite coated(silverish/light grey)
Personally I use Permatex Aviation sealant on the gaskets, dosent hurt.

Damn right! Took me years of chasing leaks to learn that you MUST use a sealant on those manifold to riser joints.

Time and heat cycling makes those "flat" gasket surfaces uneven. Even with a nice, thick gasket that joint will leak water into the motor without a sealant.

Jeff

YES!!!! Even with the new dryjoints and their impregnated gaskets. Had a persistent very slow leak of antifreeze out of my factory new w/dealer installed FWC for 9 seasons. When I replaced the elbows this spring, I took advice from this forum and used a file on the mating surfaces. Took manifold mating surface down to a uniform bright shiny metal. Used Permatex and....voila, looks as if mystery leak is gone.

Which permatex do you recommend Capt Bob?

Aviation Form-a-Gasket Sealant, liquid 3H ( the 4 oz liquid plastic jar with brush) available most everywhere.