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Old 11-28-2019, 12:02 PM   #1
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Default Water in manifolds

So I replaced all four of my exhaust manifolds this summer with Mercruiser manifolds, not aftermarket, because of all the stuff I read about them not being flat and such.
Well now Iím rebuilding my heads because I didnít like the compression numbers I was getting.
When Iíve pulled each manifold off, thereís been a little water in at least a couple of the exhaust runners on each manifold.
My machine shop said when he cut the seat in the first set of heads, he could tell there was some slight pitting or corrosion in the seats. So the water in the manifolds would explain the pitting.
Is there an expectation that being a boat, some amount of moisture is going to collect in the exhaust? I use good gaskets, and my elbows are stainless, so Iíve never questioned them, but Iíll inspect them closer while theyíre off now.
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Old 11-28-2019, 04:02 PM   #2
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Stainless steel and iron expand and contract at different rates and this may be stressing the gaskets. Have you inspected the flappers? Any condensation should not result in much if any water.
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Old 11-28-2019, 04:17 PM   #3
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Theyíre the new style flapper. They seal as well as they did when new... But I idle it for a while to the slip and then run it longer while flushing.
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Old 11-28-2019, 06:50 PM   #4
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Idle rpm should not allow any water to come up the exhaust tube, this typically happens when coming off plane to quickly.
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Old 12-04-2019, 01:32 AM   #5
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I pulled one of the elbows off today finally. The gasket was stuck to the manifold very well like Iíd expect, but the elbow didnít stick to it at all. I think I used the Sierra replacement for the OEM style with the steel core and the weird grey stuff. It was compressed, but didnít stick to the stainless. Iím thinking (hoping) thatís what was leaking while the boat sat. Anyone have similar experience and advice on what to do? I have one pair of OEM gaskets and one more pair of Sierra. I just ordered more OEM...
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Old 12-04-2019, 12:57 PM   #6
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The OEM stainless manifolds (816900c) were discontinued in 1997 due to issues with leakage. Two main issues. Porosity in the casting which could lead to leakage from manufacturing. The other was the short flange design which didn't provide the fasteners the ability to maintain the proper torque needed to avoid leaks at the joint. I think there was a bulletin on this at some point.
If you continue with these elbows, check the flatness of the mating surfaces with a straight edge to eliminate any issue from poor machining, use a sealant with the gasket to help accommodate the expansion differences Mike mentioned and check and re check the torque on the fasteners regularly.

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Old 12-04-2019, 12:59 PM   #7
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Quote:
Originally Posted by jparsons121 View Post
The OEM stainless manifolds (816900c) were discontinued in 1997 due to issues with leakage. Two main issues. Porosity in the casting which could lead to leakage from manufacturing. The other was the short flange design which didn't provide the fasteners the ability to maintain the proper torque needed to avoid leaks at the joint. I think there was a bulletin on this at some point.
If you continue with these elbows, check the flatness of the mating surfaces with a straight edge to eliminate any issue from poor machining, use a sealant with the gasket to help accommodate the expansion differences Mike mentioned and check and re check the torque on the fasteners regularly.

John


What sealant would you think?
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Old 12-04-2019, 01:36 PM   #8
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I'm a fan of the Permatex products. Ultra copper high temp.
Hopefully the elbows would never reach 700 degrees, but I like a little over engineering
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Old 12-04-2019, 01:39 PM   #9
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Also, if you have the manifold/riser/elbow off, you could pressure test on the bench before installing.
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Old 12-04-2019, 01:43 PM   #10
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Also, if you have the manifold/riser/elbow off, you could pressure test on the bench before installing.


Iíve thought about it and canít picture any way to do that without a lot of over engineering because of the way the water gets dumped into the exhaust...
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Old 12-04-2019, 04:49 PM   #11
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Quote:
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I'm a fan of the Permatex products. Ultra copper high temp.
Hopefully the elbows would never reach 700 degrees, but I like a little over engineering
I would not recommend Copper if the manifolds are raw water cooled in salt water. This will set up a battery effect with the iron and corrosion will result.
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Old 12-04-2019, 06:42 PM   #12
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Product is named 'Copper' but only refers to the color. It does not contain any Copper or any other metals.
Product data suggests use Marine applications:
Exhaust manifolds/headers, valve covers, oil pans, intake manifold end seals, water pumps, exhaust tubes
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Old 12-05-2019, 12:56 AM   #13
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Quote:
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Product is named 'Copper' but only refers to the color. It does not contain any Copper or any other metals.
Product data suggests use Marine applications:
Exhaust manifolds/headers, valve covers, oil pans, intake manifold end seals, water pumps, exhaust tubes
As long as youíre certain it doesnít contain any copper. Some Sealants and never seize are know to contain metals.
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Old 12-05-2019, 01:00 AM   #14
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As long as youíre certain it doesnít contain any copper. Some Sealants and never seize are know to contain metals.

I wouldnít worry about it too much. I have a huge chunk of copper and brass mounted on the engine with sea water in it already. And that isnít causing any unusual problems.
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Old 12-05-2019, 02:56 AM   #15
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I wouldn’t worry about it too much. I have a huge chunk of copper and brass mounted on the engine with sea water in it already. And that isn’t causing any unusual problems.
Brass is not an issue in salt water and since brass is part copper a reaction between then is not as significant. Your boat do as you please. Remember you the guy writing about water intrusion.
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Old 12-05-2019, 03:06 AM   #16
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That brass and copper are still connected to the iron block and aluminum intake, though, by coolant, sea water, and brackets...
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Old 12-06-2019, 01:26 PM   #17
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Speedy, have you seen the various techniques for filling manifolds with water then checking for leaks?
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Old 12-06-2019, 01:51 PM   #18
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Speedy, have you seen the various techniques for filling manifolds with water then checking for leaks?


No...
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Old 12-06-2019, 01:53 PM   #19
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My recent discovery was to leave the elbow attached to the manifold to remove and install. That way the elbow helps hold the manifold up and in place while trying to get the first bolts started.
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