riser gaskets????

J

johngus

Member
Dec 27, 2008
248
Amity Harbor,NY
Boat Info
1988 300 Weekender
Engines
Twin 350 Chevy
Straight Inboards
I have 88 5.7 small blocks with full closed system.I replaced the exhaust on the port engine last summer.this week noticed a coolant smell when staring cold.removed the risers and the gaskets were crap.the store only had the osco gaskets last summer so thats what i bought.I just purchased the merc gaskets.what was in there originally had a stainless plate between two gaskets.the guy tells me the new merc gaskets don't use the plates anymore.I was going to put the plates back in with merc gaskets but can't find the plates anywhere.Is it really Ok to just use the merc gasket?Just want to make sure.te gaskets are full block off because the manifolds are coolant cooled and the risers salt water cooled.Thanks
 
Really? graphite gaskets? Hmmm that's very interesting. I did not know that!
Todd
 
I don't know if they are graphite but are gray.the guy in the parts store said there was a metal plate built into them now so I will put them in over the weekend.thanks
 
Ok guy's take it easy on me, that's what they call them at my parts supplier and in looking on line and at a Merc bulletin that's what they are referred to.
 
Last edited:
sr330daguy said:
Ok guy's take it easy on me, that's what they call them at my parts supplier and in looking on line and at a Merc bulletin that's what they are referred to.
Click to expand...

I was not picking on you, no sarcasm here. I really didn't know they had them! My mechanic has been handling all my stuff for the last decade or so so I'm a little out of touch with the latest. The last time I did it I needed the metal plates. Thanks for the info.
Todd
 
tdschafer said:
I was not picking on you, no sarcasm here. I really didn't know they had them! My mechanic has been handling all my stuff for the last decade or so so I'm a little out of touch with the latest. The last time I did it I needed the metal plates. Thanks for the info.
Todd
Click to expand...

My apoligies for reading your post wrong...cheers
 
johngus said:
I have 88 5.7 small blocks with full closed system.I replaced the exhaust on the port engine last summer.this week noticed a coolant smell when staring cold.removed the risers and the gaskets were crap.the store only had the osco gaskets last summer so thats what i bought.I just purchased the merc gaskets.what was in there originally had a stainless plate between two gaskets.the guy tells me the new merc gaskets don't use the plates anymore.I was going to put the plates back in with merc gaskets but can't find the plates anywhere.Is it really Ok to just use the merc gasket?Just want to make sure.te gaskets are full block off because the manifolds are coolant cooled and the risers salt water cooled.Thanks
Click to expand...

Revised January 2001
Exhaust Manifolds, Risers and Exhaust Elbows
Models
All standard V6 and V8 gasoline engines with center outlet exhaust manifolds.
New Gaskets
IMPORTANT: These new gaskets are installed dry. No sealer is required.
P/N 27-863726 Gasket – 4 Slot.
P/N 27-863724 Gasket – Restrictor (with 2 holes and 2 slots). The 2 holes always go fore
and aft.
P/N 27-863725 Gasket – Block-off (without holes or slots). This gasket stops coolant flow.
Fastener Torque Change
33 lb-ft (45 Nm). Use this new torque on all fasteners when installing exhaust elbows or risers
 
Closed Cooled engines with the raw water from the heat exchanger going to the
90-degree fitting on bottom of the exhaust manifold:
Use P/N 27-863726 Gasket – 4 Slot between the exhaust manifold and the exhaust
elbow.
If the engine has 3 in. (76 mm) or 6 in. (152 mm) risers, use P/N 27-863726 Gasket –
4 Slot between the riser and the exhaust manifold and exhaust elbow.
\
4d. Closed Cooled engines with the exhaust manifolds closed cooled and the raw water
from the heat exchanger going to the fitting on the exhaust elbow:
Use P/N 27-863725 Gasket – Block-off between the exhaust manifold and the exhaust
elbow.
If the engine has 3 in. (76 mm) or 6 in. (152 mm) risers, use P/N 27-863725 Gasket –
Block-off between the exhaust manifold and the riser. Use P/N 27-863726 Gasket – 4
Slot between the riser and the exhaust elbow.
5. Assembly parts and torque fasteners to 33 lb-ft (45 Nm).
 
Personally, I use the SS plate and regular gaskets. Just can`t see trusing a graphite coated plate of a unknown material
 
Thanks for all the replies.i am going to assemble it now with the gaskets and over the winter try to find the stainless plates.Merc has no listing for them anymore so I only have a few weeks of boating anyway and after that I'll find them somewhere.it just seems better with the plates and a gasket on both sides.even the guy in the parts store said they probably stopped using the plates beacause it was a good design.
 
Johngus
The part you need is 27-8637251. That is OEM Merc part and runs anywhere from $9-12. It is the identical part number from my engine and I have replaced mine and those of friends several times. I have never seen a stainless plate.

Get the serial number of your engine so you can verify your parts diagram. Start here...http://www.mercruiserparts.com/selectModels3.asp?type_id=8I and find your engine, which I believe is 5.7L MIE GM 350 V-8 1988-1993 . Click it, and it will bring you to a SN range. Click that and it brings you to a list of systems. Click on Exhaust Manifold and Exhaust Elbow and check out the exploded parts diagram.

I would caution you to NOT stray from what Merc recommends when toying with these exhaust systems - the results can be catastrophic. These gaskets are very tempermental - it could be that you didn't line it up properly or you placed the gasket in place and scuffed it or pulled the elbow back off after tightening the bolts. You also said you used OSCO. Others will argue but I wouldn't touch that company's parts with a 10 foot boat hook. Stick with OEM. Buy from a Mercruiser parts dealer or order online from B0ATFIX.com. When these engines fail it is b/c of the tempermental exhaust system.

Another reason why your gasket may have failed could be b/c of corroded mating surfaces of elbow to manifold. If these surfaces are pitted or scored from years of use, the gasket will not hold coolant. That's what happened to mine. I was very fortunate to have found the problem before any ingestion.

This is what a 20 year old mating surface looks like...
105_1630.jpg


And this is what happens when the gasket fails (coolant in the exhaust passages of the exhaust manifold). Enough water gets in there and you hydrolock and your engine dies. These manifolds (all 4) were replaced upon discovery during a routine gasket replacement service (recommended interval is every third season). I now swear to do them every other season.

105_1626.jpg
 
Caution

BtDoctur in post #13 above is directing you to a part for the wrong engine. If you look at the upper left corner of his link, you'll see the engine model (EFI, which was not offered in 1988) and year 1996. You'll also see a range of serial numbers for this application. This is why I suggest you get your engine serial numbers before you buy any parts.

A quick check reveals that this part (41811) has been superceded by 27-8637251


http://www.marineengine.com/newparts/part_search.php?part_num=41811&x=19&y=7
 
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Hi johngus. I hope that you will do it right and you will finished it. Keep it up. :D
 
Use the graphite coated OEM merc gaskets, they are the only ones that seem to last {at least in my boat}
 
Rondds,
Thanks for the help.the manifolds and risers on this engine were replace last season.mine looked the same as yours.the only reason I bought the other gasket was it was all that they had in stock.The other gasket actually looked like much better quality but the truth always comes out.there was a stainless plate between 2 gaskets on the old madifolds and risers..the guy at the merc dealer said he has seen that before and it looks like a better idea and the way it used to be years ago.I knew exactly what the problem was last weekend when I started the boat and there was white smoke..it is such a crap design.I was planning to replace the gaskets this winter but it decided it wanted replacement now.I am going to reassemble everything later today.
 
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