180 (470) Mercruiser risers/exhaust manifold

[Benny67]

Does anybody know (roughly) what the lifespan of these are in Saltwater?

I have 2 of these 1987 180 (470 seems to be what everyone calls them) mercruiser motors that as of right now are both running cool as cucumbers and showing no signs of trouble. However, reading about these engines and how its so important to keep them coolmy thoughts are, at the end of this season when I pull the boat, I want to remove them and inspect them to see if they need replacing. When I do so, what are the typical signs I should be looking for?

Photos of bad ones would be nice if anybody has some to share..

Also, when you replace these do the exhaust manifolds go bad too or is it just the risers?

 

[Bondo]

Ayuh,.... I don't do 470s, but I imagine the riser life span is the same as any other that's run in the brine,....

5 to 8 years is what I hear,....

Up here in the sweetwater seas, they last yer lifetime, so long as they're drained in the winter,....

Generally speakin', risers die often, manifolds hold up abit better,....

The failure point is the gasket surfaces 'tween the 2,....
If the gasket surface rots away, it can't support the gasket, 'n water in the cylinders is the result,...

Pull 'em apart, 'n clean the castin's with a flat file or belt sander,... Dead Flat, is what yer lookin' for,...

The cast iron oughta be 'bout 1/4" wide, or wider, wherever the gasket rides, 'tween the water, 'n exhaust,....

 

[stonyloam]

The manifold is cooled by antifreeze so should last forever. The only contact that saltwater has with the 470 engine is where it dumps into the exhaust elbow after exiting the heat exchanger. So as Bondo suggests, at the end of the season check the elbow and its gasket surfaces.

 

[Benny67]

The failure point is the gasket surfaces 'tween the 2,....
If the gasket surface rots away, it can't support the gasket, 'n water in the cylinders is the result,...
,....

This explains that huge gasket I have on the port engine...That gasket is what spurred me to think about these risers. The previous owner looks like he cleaned the area up and changed that gasket probably cause of corrosion.

I sometimes notice when the motor sits for a long time ( more than a week) without starting, I get a slight smoke rising from near that gasket about a min or so after starting and it goes away in 20 seconds ...It never looses antifreeze ( I check it and the oil ever time I use the boat) But I bet this is the beginning of the end of that riser. Oh well, something to keep an eye on and hopefully it wll last the rest of the season without failing.

Thanks guys..