Checking the exhaust manifolds and risers..

[wipe_out]

We had new exhaust manifolds and risers fitted when we replaced the engine in March 2013.. So they are coming up to two years old.. I know if they fail it's pretty catastrophic, its what happened to the previous owner and why we bought the boat with a broken engine..

So how often should they be checked and what should be done when checking them? Do I need to take them apart and reassemble them at certain intervals or replace them on a regular schedule?

They are not the cheapest so hoping they don't need replacing too often.. Engine is 5.7L raw water cooled..

Thanks..

 

[lynall]

I removed the ones off of my 4.3 v6 (basically same engine just 2 cylinders short) to check them and all was good, engine new 2009, weve owned it 2 years and I read they were good for 5 years, for cost of a 4 gaskets well worth it for piece of mind, gaskets from ebay, (repower marine) again pretty much generic ie all v6 are much the same as are the v8 motors
What made me do it was the small rust bleed marks I noticed coming from the gasket joints, quick scrap of some internal surface rust and we were good to go.
Have to add ours has the neutra salt set up fitted.
Easy enough to remove, by far the hardest bit was scraping poxy old gaskets off, tough as old boots!

 

[wipe_out]

Yes, we have the rust bleeds starting around the gaskets.. Would prefer to leave it another year because I have to attempt bellows this year.. If they are good for 5 years then I should be safe leaving it for 3 so might check them next year..

 

[spannerman]

What you have to ask yourself is if there are rust bleeds on the outside, are there rust bleeds on the inside? As the land between the water jacket and exhaust is quite narrow, if in doubt, drain the manifolds before removing the riser or you risk flooding the cylinders with seawater, check the contact area, you can clean them up with a flat file but be careful to maintain even contact across the whole face of the riser and manifold. Replace gaskets, I always use a bit of silicone to allow for difference in thermal expansion between manifold and riser,and torque down to 25ft lb IIRC.

 

[annageek]

Funny this post should crop up today. My bf removed the riser to check it out on our 3.0L yesterday, as it's begining to show signs of leakiness. All looks well though other than a bit of surface rust as expected.

check the contact area

On ours, after we'd scraped away any remaining old gasket, it looks as though someone had just gone at the sealing face with an angle grinder and gay abandon! Not flat or level at all. This is on both the riser and the mating half on top of the manifold. Is this normal? It hardly seems like the thin fibre gasket will do much to seal these, regardless of the torque, due to there only being two corner bolts. What silicone do you use along with the gasket, that is happy to live at those sort of temperatures?

 

[DAW]

Have just replaced risers and sprayheads on both port and starboard engines on a 2005 Sunseeker Portofino 53 with Volvo D12s. Both were quite heavily corroded on the outside. The original parts were sent back to Manuflex to be inspected and copied for the replacements. Apparently the insides were basically OK, even though they have survived ten years/600 hours of service.

Apparently, if asked Sunseeker will recommend internal inspection after 3-5 years, depending upon the environment in which the boat it kept. For us in the SoF its five years, then a watching brief for signs of leaks from gaskets or other changes after this.

Manuflex were excellent, very competitive and very quick turnaround and I would highly recommend them if you need new parts manufactured. Local Volvo Penta service engineer did the exchange and the new parts fit perfectly.

 

[AndieMac]

...............On ours, after we'd scraped away any remaining old gasket, it looks as though someone had just gone at the sealing face with an angle grinder and gay abandon! Not flat or level at all. This is on both the riser and the mating half on top of the manifold. Is this normal? It hardly seems like the thin fibre gasket will do much to seal these, regardless of the torque, due to there only being two corner bolts. What silicone do you use along with the gasket, that is happy to live at those sort of temperatures?

Take the manifold and riser into a machine shop and have them both re-surfaced properly, don't take any chances.

I was informed by my Mercruiser tech to not use sealants at this joint, assuming both surfaces are perfectly flat and using genuine gaskets.

 

[GrahamHR]

Take the manifold and riser into a machine shop and have them both re-surfaced properly, don't take any chances.

I was informed by my Mercruiser tech to not use sealants at this joint, assuming both surfaces are perfectly flat and using genuine gaskets.

The Mercruiser petrol V6/ V8 set up is usually "dry joint"; no water passing internally from the manifolds to the risers. External pipework does that job. Volvo Penta persist with using a "wet joint" set up, with quite a narrow seal between the water and the exhaust passage. VP now recommend the use of a copper containing sealer on the manifold to riser gaskets ( there is a service bulletin about this). Genuine gaskets seem to be steel + graphite foil, a very effective sealing combination. VP are also quite specific about the preparation of the mating surfaces. I can recommend the Neutrasalt system; the risers on my previous boat lasted 8 seasons and didn't really need changing ( but I did, as I got a pair of OEM ones very cheap on Ebay !)

 

[spannerman]

The Mercruiser petrol V6/ V8 set up is usually "dry joint"; no water passing internally from the manifolds to the risers. External pipework does that job. Volvo Penta persist with using a "wet joint" set up, with quite a narrow seal between the water and the exhaust passage.)

That is only on the later type of Mercruiser manifold, the majority out there are the early type with seawater passing through if open cooling and coolant and seawater separated by a blocking gasket on a closed cooling system.
I have closed cooling and on this setup the manifolds run much hotter as they are at 80c the same as the engine block as they are part of the closed coolant circuit. The risers run cooler as they have seawater cooling them.
Because of the difference in temperature in a relatively small area there is the potential for differential expansion at the joint, so although the manual doesn't specify sealant I use Volvos own RTV silicone sealant which is a belt and braces approach and has worked perfectly, as the two times I have removed the risers for inspection the joint has been in perfect condition.

 

[mlines]

The Mercruiser petrol V6/ V8 set up is usually "dry joint"; no water passing internally from the manifolds to the risers. External pipework does that job. Volvo Penta persist with using a "wet joint" set up, with quite a narrow seal between the water and the exhaust passage. VP now recommend the use of a copper containing sealer on the manifold to riser gaskets ( there is a service bulletin about this). Genuine gaskets seem to be steel + graphite foil, a very effective sealing combination. VP are also quite specific about the preparation of the mating surfaces. I can recommend the Neutrasalt system; the risers on my previous boat lasted 8 seasons and didn't really need changing ( but I did, as I got a pair of OEM ones very cheap on Ebay !)

So just to clarify, I have a 2007 350MAG.

It definitely has pipework to the risers but if it does not have pipework to the manifolds then I do not have to worry about manifold corrosion? I only need to check the risers?

This is a diagram from a 2001 workshop manual which shows the circulation through both the manifolds and the risers, if I check mine and it does not have the manifold pipe work then I am ok?

Martin

 

[spannerman]

All V engine manifolds have a pipe going to the underside in the centre, if its seawater cooled then the only other pipe will be to the front side of the riser.
If however you have a pipe coming from the top of the manifold just in front of or occasionally behind the riser then you have freshwater cooling on the manifold alone, risers are ALWAYs seawater cooled.
The later type have a cast elbow exiting from the riser on the front and rear face which connects to the manifold immediately underneath, this is usually a seawater cooled system.
Just to clarify Mercruiser have 3 variants,
totally seawater cooled,
partial freshwater cooled with just freshwater in the block and seawater in the manifolds and risers,
and full freshwater cooling with freshwater in the block and manifolds and just the risers seawater cooled.
You can tell what you have by the plumbing.

 

[mlines]

So there will always be water in the manifold, its just whether it is seawater or freshwater?

 

[julians]

It was around 2002 that mercruiser switched to what are known as dry joint manifolds. These don't have the weakness of the old system where corrosion between water jacket and exhaust passage at the mating surface between risers and manifolds would cause water to enter the cylinders .

The dry joint manifolds pass the water through a distinct pipe that runs separately to the join for the exhaust gasses, so if this water jacket joint corrodes water can only flow externally and not into your cylinders.the distinct pipe is part of the casting of the manifold and riser , it is not a rubber pipe, so can be quite hard to spot unless you know what you're looking for. It still doesn't stop a problem if the water jacket actually cracks in the manifold or riser though, but most failures due to corroded manifold were not due to this, they were due to the corrosion at the mating surface.

That diagram in the previous post shows an old style wet joint manifold. If you look at the same engine, but for say 2006, you'll see the manifolds and risers are different with a separate cast pipe. The gaskets that seal the mating surface are also different.

I had a 2006 sea ray from new with the dry joint manifolds on raw water cooling, I sold it last year, but the manifolds were fine after 7 years /400 engine hours of use in saltwater, that boat was kept in saltwater 365 days per year. If I had kept the boat I was going to change them at 8 years, just in case of the problem where the water jacket cracked.

 

[spannerman]

Yes there is always water/coolant present as you say depending on which system you have, and always seawater in the riser up to the bottom of the elbow as if its higher than that it will run out down the exhaust pipe.

 

[AndieMac]

,

....................Because of the difference in temperature in a relatively small area there is the potential for differential expansion at the joint, so although the manual doesn't specify sealant I use Volvos own RTV silicone sealant which is a belt and braces approach and has worked perfectly, as the two times I have removed the risers for inspection the joint has been in perfect condition.

Yes indeed SM, I have the newer dry joint system on my re-powered boat, but with the old wet joint, talking of belt and braces, I would re-tension the riser bolts during the season....just in case