Stuck! Need advice ASAP 7.4 motor knock- need to get home!

MasterFab said:
The earlier elbows were bolted to the manifolds with a gasket that sealed both the water and the exhaust. The exhaust was directed from the middle of the manifold into the middle of the elbow, while the water surrounded the exhaust flow, and was sealed by this same gasket between the manifold and elbow. If the gasket failed, water could enter the exhaust stream, and work its way back into the engine under specific conditions.

The dry joint manifold and elbow are a bit different. The gasket between the two only seals exhaust gases. For the cooling water, a hose connects the top of the manifold to the bottom of the elbow, via a nipple threaded into each. So, the cooling water fills the manifold, then passes out of the manifold into this short length of hose, and then flows back into the elbow just above the gasket / flange. This way, the flange strictly seals exhaust gases, and is "dry". If the gasket fails, an exhaust leak develops, but no water intrusion takes place.

My offer of help still stands, Russ... (but don't think you're getting out of that drink!)

Dale
Click to expand...

Do you know where one can obtain some more information about this, drawings, technical data etc. This sounds very interesting, especially this part, "If the gasket fails, an exhaust leak develops, but no water intrusion takes place."

Thanks
 
Pseudomind said:
Do you know where one can obtain some more information about this, drawings, technical data etc. This sounds very interesting, especially this part, "If the gasket fails, an exhaust leak develops, but no water intrusion takes place."

Thanks
Click to expand...


Does anyone have link to a parts breakdown diagram of this system so one might be able to visualize how this works? This dry manifold,hose combination.

Thanks
 
Pseudomind go to this link, it explains how the system works. http://www.ebasicpower.com/faq/dryjointexhaust.htm

I've looked for a dry joint kit for 7.4 but I don't think Merc. makes them yet. I don't need them now and may be able to go another season with the present setup. Hopefully by the time I need them, 2013, I can find one. It really does seem to be the hot setup.
 
Last edited:
That link provides a good description of how the system works, with illustrations for the small block engines. The 8.1s are a implemented a bit differently, since these engines use a tubular elbow, not a cast elbow like the small blocks. The difference is that instead of using the orange O-rings, the connection on the 8.1s is via a short length of hose. The benefits are the same, however.

Dale
 
The 8.1's and 7.4's exhaust manifolds are not interchangable for the record.

They do not make dry joint exhaust systems for the 7.4's either.

Do a quick search on here and several people have looked into it without luck.

Doug
 
Russ Calasant said:
Rod, how much?
Click to expand...
Russ, not sure... if your interested, you would have to contact Alan at HiTek and make him an offer... You know how Alan is, the like to negotiate.
I showed the two I took off to a CSR friend here in MD who has a 400 EC. He brought them to a machine shop, for an estimate, and they went ahead and repaired them. Unfortunately, these are for V Drive and not straight inboards... I still need to pull of the one set that are on the the boat. HI-TEK told me to pull them off and inspect them... I plan on doing that after I winterize the boat. Alan can't imagine why they cracked, and he told me that I am only one this has happened to.

Since they are one piece and the raw water exits so far away from the engine, I can't imagine every having a water ingestion problem with these manifolds...
 
Is there room to add a 6" riser extension to help with water reversion on your setup?

I have seen these used in conjunction with the new style mufflers as a solution to that problem.

Doug
 
dicor said:
Pseudomind go to this link, it explains how the system works. http://www.ebasicpower.com/faq/dryjointexhaust.htm

I've looked for a dry joint kit for 7.4 but I don't think Merc. makes them yet. I don't need them now and may be able to go another season with the present setup. Hopefully by the time I need them, 2013, I can find one. It really does seem to be the hot setup.
Click to expand...

MasterFab said:
That link provides a good description of how the system works, with illustrations for the small block engines. The 8.1s are a implemented a bit differently, since these engines use a tubular elbow, not a cast elbow like the small blocks. The difference is that instead of using the orange O-rings, the connection on the 8.1s is via a short length of hose. The benefits are the same, however.

Dale
Click to expand...


Hey I want to thank you both. I have a tall risers on each engine with the small elbow shaped hoses connecting from the manifold. The link answered more than I had, but what I am looking for is diagram of how the exhaust and water are flowing through on the inside from when it enters the manifold. I understand where the exhaust comes from off the engine block, it is just how the water is combined with the exhaust and out the riser and elbow and out the exhaust.

http://i54.photobucket.com/albums/g117/pseudomind/Picture028a.jpg

I am guessing I have at least about six inch risers, so I guess you can see why I am interested in the dry gasket and water routing.

http://i54.photobucket.com/albums/g117/pseudomind/Picture026a.jpg

There is a lower small elbow water hose below the one shown here which is connecting to the elbow.

Thanks again
 
Last edited:
To make a dry joint on 7.4 put block off gaskets in and run hoses from manifold to riser if no 3 or 6 inch spacer block is used on 310 mpi the manifold is raw water cooling un like 96 witch had antifreeze in ext manifold. You will need to check to se if you have the early fix with the resinators in ext hoses 8 inches down from riser with flat end tords back of boat. On 96 manifold stays more even temp since it does not go dry every time you shut down engine and they did not get water intrusion when they had even temp.
 
I would strongly discourage anyone from attempting this "solution". Re-directing the water from the manifold to the elbow via the use of block off gaskets provides absolutely no benefit, and will hasten the demise of the manifold/elbow seal. If the elbow gasket were to fail, as they all inevitably do, the water will still enter the exhaust stream at the same location - by passing from the manifold water jacket into the exhaust plenum. By preventing cooling water from flowing through this transition area, the gasket failure will be hastened, since a "hot spot" will be created. The differing expansion and contraction rates of the castings at this point will simply accelerate the gasket failure. Secondly, the water flow rate could be altered, possibly resulting in further damage elsewhere in the system.

The advantage of the Mercruiser dry joint lies in the design of exhaust castings - a system that was designed and tested by engineers with considerable resources at their disposal. There is more clamping force, less flexure, and more clamping area as compared to the old style exhaust system. And the cooling water is no longer in such close proximity to the engine exhaust.

To make the older system last as long as possible, follow the Mercruiser recommended maintenance schedule, and replace the specified gaskets per Mercruiser procedures, using the proper torque values and sealant (Loctite 510). Conduct an inspection of the components at each disassembly, and watch for signs of exterior water leakage, which normally first manifests as light rusting at the flange interface. If it starts to leak on the outside, it is a safe bet that internal leakage has begun as well.

Dale
 
MasterFab said:
I would strongly discourage anyone from attempting this "solution". Re-directing the water from the manifold to the elbow via the use of block off gaskets provides absolutely no benefit, and will hasten the demise of the manifold/elbow seal. If the elbow gasket were to fail, as they all inevitably do, the water will still enter the exhaust stream at the same location - by passing from the manifold water jacket into the exhaust plenum. By preventing cooling water from flowing through this transition area, the gasket failure will be hastened, since a "hot spot" will be created. The differing expansion and contraction rates of the castings at this point will simply accelerate the gasket failure. Secondly, the water flow rate could be altered, possibly resulting in further damage elsewhere in the system.

The advantage of the Mercruiser dry joint lies in the design of exhaust castings - a system that was designed and tested by engineers with considerable resources at their disposal. There is more clamping force, less flexure, and more clamping area as compared to the old style exhaust system. And the cooling water is no longer in such close proximity to the engine exhaust.

To make the older system last as long as possible, follow the Mercruiser recommended maintenance schedule, and replace the specified gaskets per Mercruiser procedures, using the proper torque values and sealant (Loctite 510). Conduct an inspection of the components at each disassembly, and watch for signs of exterior water leakage, which normally first manifests as light rusting at the flange interface. If it starts to leak on the outside, it is a safe bet that internal leakage has begun as well.

Dale
Click to expand...


I don't know about the rest of y'all, but I find it a pleasure to read a post by someone who can write English properly and use correct punctuation, and the fact that his posts are based on knowledge and experience, not what he thinks he knows or read recently.

Thanks for your contribution to CSR, Dale.
 
fwebster said:
I don't know about the rest of y'all, but I find it a pleasure to read a post by someone who can write English properly and use correct punctuation, and the fact that his posts are based on knowledge and experience, not what he thinks he knows or read recently.

Thanks for your contribution to CSR, Dale.
Click to expand...

Frank,

I actually had the opportunity to meet Dale and had the tour of his completely restored 340DA. The WOW factor was huge. I know that Dale had a different thread regarding his project with details and performance numbers. But, I know that he took few folks for a demo ride and demonstrated how his boat performs. From what I recall his WOT was around 40KTS (Dale, please correct me if I'm wrong). My point is that he managed to make a basic 340DA perform like a race boat leaving TONs of space in the engine room. BTW, as you can imagine, the fuel burn numbers were just as good as the speed improvement compare to other 340s out there.

Dale could be just a recreatinal boater (I don't know details of his background), but after speaking with him and seeing his work in person it wasn't hard to notice that he really knows his stuff and could be more qualified than a number of professional mechanics out there.
 
Last edited:
MasterFab said:
I would strongly discourage anyone from attempting this "solution". Re-directing the water from the manifold to the elbow via the use of block off gaskets provides absolutely no benefit, and will hasten the demise of the manifold/elbow seal. If the elbow gasket were to fail, as they all inevitably do, the water will still enter the exhaust stream at the same location - by passing from the manifold water jacket into the exhaust plenum. By preventing cooling water from flowing through this transition area, the gasket failure will be hastened, since a "hot spot" will be created. The differing expansion and contraction rates of the castings at this point will simply accelerate the gasket failure. Secondly, the water flow rate could be altered, possibly resulting in further damage elsewhere in the system.

The advantage of the Mercruiser dry joint lies in the design of exhaust castings - a system that was designed and tested by engineers with considerable resources at their disposal. There is more clamping force, less flexure, and more clamping area as compared to the old style exhaust system. And the cooling water is no longer in such close proximity to the engine exhaust.

To make the older system last as long as possible, follow the Mercruiser recommended maintenance schedule, and replace the specified gaskets per Mercruiser procedures, using the proper torque values and sealant (Loctite 510). Conduct an inspection of the components at each disassembly, and watch for signs of exterior water leakage, which normally first manifests as light rusting at the flange interface. If it starts to leak on the outside, it is a safe bet that internal leakage has begun as well.

Dale
Click to expand...


I was in my own way asking these same questions which Dale has nicely answered. I have to agree with Dale from just looking at Mercruiser material diagrams, installing a dry gasket seems like it would play havoc, especially with heat. I am for myself just trying to visualize how/where the water and exhaust mix and go out the exhaust, without any water getting back into the exhaust portion of the manifold. From looking at the Mercruiser 8.1 manual's Cooling Section graphic and the Mercruiser parts manual diagram. It shows water entering the rails, then I am guessing flowing through the manifold and out the top of the manifold via hoses into the riser in my case and then out another hose into the elbow.

Now with the manifold/riser or elbow gasket having such a large diameter hole in the center, what prevents water from just falling back via gravity into the exhaust manifold plenum area. Does the exhaust gas have enough pressure to prevent this? This may be part of the reason these 8.1's are designed to drain out raw water when shut down, but again what might happen if an engine misfired a couple of times, would this not possibly allow water in-gestation back into the manifold?

Just exactly what does the air actuator water connection from the water rail do?

I would sure like to be able to see or be told just how these manifold, riser, elbows work ? A picture would be really nice.


Now a biggie, Will the new dry manifolds work on a 2002 model 8.1 engine, the 370 horsepower, or is this just designed for newer model engines?

These questions may seem to be overkill, but for me they actually help me with my boat maintenance, knowing how items function. I would speculate the answers to my questions will also help a few others here on CSR.


Thanks
 
Last edited:
Here is an interesting read on elbow design and the effects the internals have on possile water intrusion.

http://www.michel-christen.com/ExhaustElbows.pdf

So the big question is for those of us that have the 7.4 what can be done to prevent problems.
Would changing the half FWC system out to a full system work?
 
Last edited:
That's the million dollar question, what do I do to stop the problem? Now that I am putting in a new motor, maybe two, how do I ensure no further water ingestion? The answer cannot be that every winter I have to pull off the manifolds for visual inspection. I was always told that visual inspection is not nearly sufficient. The boat ran for 14 years and 700 hours without problems and now I'm terrified I'm going to spend $20k only to have it happen again.
 
Russ,

Is your boat equipped with log style exhaust, or water lift mufflers? I recall this vintage was log style, with the water lift transition a bit later. Can you please confirm which you have?

Frank,

I really appreciate the kind words. I know I am the new guy, but I really appreciate the sense of community on this site - it's the only forum I am a member of. I know you've been here a long time, and are highly regarded by the other members, so it means alot to have your support. And if you ever want to sell that 450....

Alex,

Thank you as well - and you are close on the numbers. Top speed turned out to be 38.6 knots (2 way average), while my normal cruise at 3200 - 3400 RPM ranges from 25.5 to 28.5 knots, respectively. I can maintain plane down around 15 knots at 2500 RPM, with the enlarged tabs fully deployed. The range between 2500 and 3000 RPM will be excellent for maintaining plane in rougher conditions, if it isn't so rough I have to drop to hull-speed completely. Fuel consumption is hovering right around 1 MPG at cruise speed, which is about 8-10% better than the stock vessel configuration.

Russ, I'll build a nice custom water lift exhaust for you, if your interested. All Class 1 resins, custom bends, isolated mufflers, so quiet and free flowing, with no water ingestion problems.....hhhmmmm.....

Dale
 
Fascinating piece on exhaust elbows. Also interesting how a post-mortem can be done to determine cause of ingestion.

For my engines, which are Gen IV, based on their serial numbers, the elbow is 807988A03. This article makes no mention of this part number. I'll venture a guess that it has superceded 807988A02, which the article deemed to have "...no indication of an effective vacuum-break." I wonder if the ...A03 variant is an improved design (?)
 
You must log in or register to reply here.

Forum statistics

Threads
113,248
Messages
1,429,275
Members
61,128
Latest member
greenworld
Back
Top