Water in manifolds

[speedysprocket]

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 I’m rebuilding my heads because I didn’t like the compression numbers I was getting.
When I’ve pulled each manifold off, there’s 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 I’ve never questioned them, but I’ll inspect them closer while they’re off now.

[mmwjr]

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.

[speedysprocket]

They’re 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.

[mmwjr]

Idle rpm should not allow any water to come up the exhaust tube, this typically happens when coming off plane to quickly.

[speedysprocket]

I pulled one of the elbows off today finally. The gasket was stuck to the manifold very well like I’d expect, but the elbow didn’t 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 didn’t stick to the stainless. I’m thinking (hoping) that’s 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...

[jparsons121]

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

[speedysprocket]

Originally Posted by jparsons121

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?

[jparsons121]

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

[jparsons121]

Also, if you have the manifold/riser/elbow off, you could pressure test on the bench before installing.

[speedysprocket]

Originally Posted by jparsons121

Also, if you have the manifold/riser/elbow off, you could pressure test on the bench before installing.

I’ve thought about it and can’t picture any way to do that without a lot of over engineering because of the way the water gets dumped into the exhaust...

[mmwjr]

Originally Posted by jparsons121

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.

[jparsons121]

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

[mmwjr]

Originally Posted by jparsons121

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 you’re certain it doesn’t contain any copper. Some Sealants and never seize are know to contain metals.

[speedysprocket]

Originally Posted by mmwjr

As long as you’re certain it doesn’t contain any copper. Some Sealants and never seize are know to contain metals.

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.

[mmwjr]

Originally Posted by speedysprocket

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.

[speedysprocket]

That brass and copper are still connected to the iron block and aluminum intake, though, by coolant, sea water, and brackets...

[jrsick]

Speedy, have you seen the various techniques for filling manifolds with water then checking for leaks?

[speedysprocket]

Originally Posted by jrsick

Speedy, have you seen the various techniques for filling manifolds with water then checking for leaks?

No...

[speedysprocket]

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.

[shrew]

Originally Posted by speedysprocket

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.

Are you removing/installing it with the hoses on? I would think it would be lighter an easier without the elbow.

A friend showed me a trick he uses. He took a couple of long bolts that match the thread pattern of the manifold mounting bolts. He then cu the heads off, , essentially making a stud, and then ground a notch on the end of the bolt for a flathead screwdriver.

He pulls one bolt, then greases and installs the homemade stud. He pulls a second bolt and replaces with another greased stud.
now he removes the rest of the bolts, leaving the studs in place. He slides the manifold off, again leaving the studs in place.

Now install the new manifold using the studs to hold the manifold in place.

Install the bolts. Now remove each stud and replace with bolts one at a time.

Now torque down the bolts.

This process allows you to easily replace manifolds alone and allows the gasket to stay in place as well.