Newb? Understanding manifolds and risers

[tubenewb]

Hey all. Have two 3.0's torn down. Both of them I suspect water leak from the manifold system.
This particular head from my 88 shows sighns of water damage only on the intake ports..Head and manifold.

I do plan on getting a new manifold .Before I get that far though, I have been reading a little more here and I have stumbled upon "check out the riser"

So I guess I understand that the exaust and water actualy mixes and exits after the bend in the riser...

1. What is the purpose of the high elbow? Is it to make sure water doesnt come back up ?
2. I guess I can assume if the riser is leaking it has the same effect as a leaking manifold..but it would only let water into the exaust ports right?

Just trying to understand it better both working and failing..

Thanks
Chris P.

 

[boat127]

Re: Newb? Understanding manifolds and risers

hi chris the elbow is a siphon break. there is also a rubber exhaust flapper in the exshaust pipe where the rubber boot is. that flapper valve prevents water from entering the engine when you slow down from plane/high speed suddenly. the water and exhaust mix together at the riser

 

[bruceb58]

Re: Newb? Understanding manifolds and risers

hi chris the elbow is a siphon break.

Not a siphon break. Its purpose is twofold, to keep the exhaust high enough that water does not enter the exhaust due to the level of the boat and to mix the water and the exhaust so that it is cooled as it enters the exahust tubes that lead to the stern drive.

 

[Simoniz]

Re: Newb? Understanding manifolds and risers

And if the riser is leaking, either rusted through or at the manifold to riser join, between water jacket and exhaust gas path, then water will run down the exhaust passage into the engine cylinders.

 

[tubenewb]

Re: Newb? Understanding manifolds and risers

And if the riser is leaking, either rusted through or at the manifold to riser join, between water jacket and exhaust gas path, then water will run down the exhaust passage into the engine cylinders.

Hmmm..So I guess its safe to assume if there is only evidence of water in the intake ports and runners than the elbow is good..All my intake valves and ports are rusty on the 88

I guess its possible for these things to leak and or crack in many possible ways..

 

[Alpheus]

Re: Newb? Understanding manifolds and risers

If you are spending the cash to rebuild your engines don't cheap out by using your old risers. Get new ones and you wont have to worry about it...

Here is a pic of manifolds and risers for a V-8. Its the same concept as yours. Your intake and exhaust are the cast as one piece but the riser is the same...

 

[tubenewb]

Re: Newb? Understanding manifolds and risers

Thanks for the cutaway pics Aplheus..
And thanks for the info guys, helps paint the picture now..

Just wish I new for certain, but judging by the age these motors probably had manifold leaks...
The exhaust looks free of water..Has anyone seen a 3.0 manfiold leak in this way before?

 

[bruceb58]

Re: Newb? Understanding manifolds and risers

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[Technorunner]

Re: Newb? Understanding manifolds and risers

Thanks for the cutaway pics Aplheus..
And thanks for the info guys, helps paint the picture now..

Just wish I new for certain, but judging by the age these motors probably had manifold leaks...
The exhaust looks free of water..Has anyone seen a 3.0 manfiold leak in this way before?

In the 3.0 correct me if im wrong but the exhaust and inlet manifold are the same so if the water jacket on the manifold before the riser are rusted through then it con be a leakage both to exhaust and to inlet.
But if the engine have been unused a while and not winterized then dew and moist can get down through the carb and make rust in the intake ports and manifold. So if the manifold is rusted in the ports as well, then remove the carb and se if the rust starts at the carbmounting port.

Hope you understand even though my English isent the best.

//Andreas

 

[tubenewb]

Re: Newb? Understanding manifolds and risers

In the 3.0 correct me if im wrong but the exhaust and inlet manifold are the same so if the water jacket on the manifold before the riser are rusted through then it con be a leakage both to exhaust and to inlet.
But if the engine have been unused a while and not winterized then dew and moist can get down through the carb and make rust in the intake ports and manifold. So if the manifold is rusted in the ports as well, then remove the carb and se if the rust starts at the carbmounting port.

Hope you understand even though my English isent the best.

//Andreas

I understand what you are suggesting...I guess its even possible the flame arrestor was left off out in the rain..I did find a second stud laying around on the floor...
What do you guys think? Here are some pics.

 

[bruceb58]

Re: Newb? Understanding manifolds and risers

Looks like there may have been a lot of water in that intake manifold at one time.