Mercruiser 120, maintenance / replacement of exhaust manifold, riser and flapper.

[Starcraft Enterprise]

I still consider myself new to inboards. I have read some of the info. on here that I could find but still have some newby questions, so I gave up searching and posted.
1969 Mercruiser 120-
I suspect it still has the original manifold and riser / elbow. How often should they be replaced?
Also was wondering, what is the purpose of the flapper, where exactly is it located and how often should it be replaced?

 

[Don S]

Re: Mercruiser 120, maintenance / replacement of exhaust manifold, riser and flapper.

I have read some of the info. on here that I could find but still have some newby questions, so I gave up searching and posted.

Did you search the Sthickies at the top of this forum? They are usually there for a reason.

I suspect it still has the original manifold and riser / elbow. How often should they be replaced?

They get replaced when they start going bad. Overheating, water in the cylinders, things like that.
It usually starts out small, but if you just shrug it off and let it go too far, then is when you loose.
In fresh water, you may never need new manifolds, but after 40 years, it might be time to pull the riser off and have a look see what thing look like.

The flappers SLOWS DOWN surges of water coming from the stern that could allow water back into the water. It will NOT completely prevent water from getting there, it just slows down the big surges.

 

[Starcraft Enterprise]

Re: Mercruiser 120, maintenance / replacement of exhaust manifold, riser and flapper.

Did you search the Sthickies at the top of this forum? They are usually there for a reason.


They get replaced when they start going bad. Overheating, water in the cylinders, things like that.
It usually starts out small, but if you just shrug it off and let it go too far, then is when you loose.
In fresh water, you may never need new manifolds, but after 40 years, it might be time to pull the riser off and have a look see what thing look like.

The flappers SLOWS DOWN surges of water coming from the stern that could allow water back into the water. It will NOT completely prevent water from getting there, it just slows down the big surges.

I have read the sticky's before but did not remember reading about these questions.
So I went back and read them again, but I still do not see the answers to my questions.
Which sticky is it in?

 

[Starcraft Enterprise]

Re: Mercruiser 120, maintenance / replacement of exhaust manifold, riser and flapper.

Did you search the Sthickies at the top of this forum? They are usually there for a reason.


They get replaced when they start going bad. Overheating, water in the cylinders, things like that.
It usually starts out small, but if you just shrug it off and let it go too far, then is when you loose.
In fresh water, you may never need new manifolds, but after 40 years, it might be time to pull the riser off and have a look see what thing look like.

The flappers SLOWS DOWN surges of water coming from the stern that could allow water back into the water. It will NOT completely prevent water from getting there, it just slows down the big surges.

When I pull the riser off, what should I be looking for?

 

[cr2k]

Re: Mercruiser 120, maintenance / replacement of exhaust manifold, riser and flapper.

Rust, scale, more rust. As the manifolds age they rust on the inside. The rate at which they rust varies determined by the water they are used in. i.e. brackish, salt, etc. When they rust they expand on the inside and narrow the passage. This causes a restriction for the out going water. Water in can only cool the engine/manifolds if it is allowed to escape. Sometimes you can "rod" out a lot of loose rust and clean out the manifold and prolong it's service life. There is no real set life of a manifold due to the reasons stated above. A set of manifolds used at lake Tahoe will probably last forever vs. an ocean boat.
When you experience overheating or even just now the boat runs a little warmer than it did a year ago and you have changed the impeller (every other year) and the thermostat but no improvement it is time to check the exhaust manifolds and risers for restrictions. This condition is also present (to a lesser degree) in the block and head, but they usually have larger (wider/more open) passages which wont plug up as the manifolds can. This is another reason to drain your engine block annually to allow any rust or sediment to escape.