Riser gasket delima (7.4 mpi)

nickysc

nickysc

New Member
Jul 1, 2007
581
Springfield SC
Boat Info
270se sundancer
Engines
7.4mpi w/BravoIII
This winter I've been going through transome assembly, had to pull engine to do all that was needed. While engine was out I replaced riser gaskets. Here is my question, I ordered gaskets from my sea ray dealer, hopeing there would not be any question on getting the correct gaskets. Gave engine model MCM 7.4 MPI # OL324774, also needed to know that the riserswere 3" high. The gaskets arrived, I took old ones out and they were different from the new ones. Called parts guy and questioned him about the difference. I received 2 with the slots on all four sides and 2 with 2 slots and a small hole on 2 sides, my instructions were to install the 4 slotted on top of the manifold, and the 2 slotted on the riser beneith the elbo.
After reading this threadhttp://clubsearay.com/forum/showthread.php?t=15534 I am very concerned. Has anyone ever used this combination of gaskets(with 3" risers).
on the top of the riser there is a grove made, that is beneith the gasket , that connects all the water ports, flues(what ever you call them) together. Will this allow the water to escape and not get trapped in the riser.
I am new to boat engines and don't know if the water needs to escape the risers as quickly as possible, or if it needs to hang around for a few seconds to build some back pressure on the system, or prehaps cool the rises more by being restricted on 2 sides. Also I am worried that the restriction could cause damage to the flaps in the "Y" pipe.
Ive never had a heating prob. with this engine. The only thing that I can think of, is when the outside temp is real hot (mid to upper 90) if I don"t let engine idle for awhile after long periods on plane, and try to start it befor the bildge cools down it will be vapor locked. This raises the question, are the riser temps to high with the four slotted gaskets above and below the riser.
Do I need to use what merc. sent, or put back what I took out. Thanks for all the input I can get. Nicky
 
I have good news and bad news for you. The good news is that the 3" risers and elbows for one of my 7.4s is downstairs in the garage. All four gaskets are the four slot type. The bad news is that my 7.4s have closed cooling and turn a Borg Warner 5000 series V-drive transmission, not a sterndrive, so your setup may differ.

What came off?

Best regards,
Frank
 
Frank the 4 slotted came off. My first thought was, IF IT AINT BROKE DON'T FIX IT, go back with the 4 slotted ones. The I began to think (most of the time , thats not a goodthing) What if the bilge heat is too high because the gaskets were not the rightones. Maby domping the water to quick. I will put back what came out unless any one tells me that there is a reason for the combination that Merc. sent me. Thanks Nicky
 
See if this helps... If you put the cursor on the gasket it will tell you what type of system it is used for...
 
Thanks, Mark. According to the link, the gaskets that I have are for raw water cooling, So that means that they are the right ones. I have no additional cooling other than the raw water pump. Nicky
 
nickysc said:
Frank the 4 slotted came off. My first thought was, IF IT AINT BROKE DON'T FIX IT, go back with the 4 slotted ones. The I began to think (most of the time , thats not a goodthing) What if the bilge heat is too high because the gaskets were not the rightones. Maby domping the water to quick. I will put back what came out unless any one tells me that there is a reason for the combination that Merc. sent me. Thanks Nicky
Click to expand...

If that's what came off then that is what should go on. The cooling system requires a certain mass of water to carry off the heat. Reduce the mass and you reduce the amount of heat that can be absorbed. The only way to get more cooling water mass into the cooling system is to run a greater volume of water. Therefore, use the four port gasket to move a sufficient volume of raw water though the cooling system. Volume, you need plenty of volume for the big block engine.

Best regards,
Frank
 
Do a bit O' research. There are parts stores and Mercruiser website that show breakdown installations for the manifold and risers and proper gasket configurations. Mercruiser has a phone number for Fon duLac, Wi and the technical guys can advise you correctly. (careful of taking a salespersons advise). Not saying in your case, but an improper gasket and flow plate install can lead to hot spots and or water entry into the exhaust ports, just to name a few. I'm sure there are others on CSR that can lend you support too. Good Luck.
 
I would like to talk to a mercruiser rep. Does anyone know the phone # or an email . At this point I'm agreeing with Frank. But the diagrams on the web indicate that I've been running the wrong gasket between the riser and elbo. I don't think it will cause a problem to go with the 4 slotted in both places. I'm wondering why merc. reccomends the 2 slotted plus the small holes, rather than the 4 slotted. Thanks for all in put Nicky
 
The 454 that I help a friend do had 2 different gaskets. It was raw water cooled.

The gasket with the 4 slots went on the manifold, the riser/spacer, and then the gasket with the 2 slots and 2 small holes. The 2 small holes went fore and aft. Then the elbows.
 
With new gaskets installed(four slotted on top of manifold, 2 slotted on top of rises beneath elbo) placed a gardenhose on the 1 fitting thats located on the bottom of the manifold, there is 60lbs of pressure and a 5/8 hose. I don't know how this compares to the water flow from the engine. There was no sign of restriction. Water flowed out as fast as I could put it in.
Does this tell me anything at all.
Nicky
 
Nicky- I do not know for a fact on your boat what is correct - but I have a 1999 7.4 MPI raw water cooled and I have used the 4 slot gaskets on both sides and it runs at 175 (per the gage) consistantly.
 
After 3 days of research, phone conversations, I've decided to install my riser gaskets. An engineer that works for Cummins Marine was my final source. I AM IN NO WAY RECCOMENDING THIS TO ANYONE, you should consult you'r dealer or manfactor before you make any changes to anything on you'r boat. Now that the disclaimer is out of the way.
Mercruiser reccomends on my engine ser# to install the2 slotted gasket on top of the manifold, the 4 slotted gasket above the spacer block, beneith the elbow. This will cause the water to move slower through the manifold and allow it to move freely throgh the riser. This will reduce the heat in the manifold considerably (how much, I don't know), thus reduceing the heat build up in the bildge.
With some fair weather and a little luck I should get my engine back in boat this wknd. I should be able to ck things out in the next few wks. I will post the results of this change, or if there is no difference. Nicky
 
nickysc said:
After 3 days of research, phone conversations, I've decided to install my riser gaskets. An engineer that works for Cummins Marine was my final source. I AM IN NO WAY RECCOMENDING THIS TO ANYONE, you should consult you'r dealer or manfactor before you make any changes to anything on you'r boat. Now that the disclaimer is out of the way.
Mercruiser reccomends on my engine ser# to install the2 slotted gasket on top of the manifold, the 4 slotted gasket above the spacer block, beneith the elbow. This will cause the water to move slower through the manifold and allow it to move freely throgh the riser. This will reduce the heat in the manifold considerably (how much, I don't know), thus reduceing the heat build up in the bildge.
With some fair weather and a little luck I should get my engine back in boat this wknd. I should be able to ck things out in the next few wks. I will post the results of this change, or if there is no difference. Nicky
Click to expand...
FWIW - I just open my merc manual Number 23. Under the Riser section (6" is what I have) this note is under the assembly drawing.

"NOTE: Later models will have an open gasket (four slots) instead of a restrictor gasket (two slots and two holes). If replacing gaskets, it is acceptable to replace the old gaskets with the open gaskets. Be sure that the same type of gasket is used on both manifolds."
 
Launched boat today, checked all the winter work. Everything was fine. The engine ran 170 on plain for long periods of time. Also was cool at idle speeds . Pulled bilge covers several times, manifolds were cool to the touch, riser was also cool, the elbo that goes to theY pipe was a little warm. So the new gasket arrangement seems to do the trick (2 slotted with 2 small holes on the manifold, 4 slotted on top of spacer block), The real test will be when the temps get close to 100, time will tell. Also the water temp was 62 today. Nicky
 
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