Why do people change or replace Risers or manifolds?

[suprasam]

I have read some articles this summer where some people have changed the riser an some manifolds. Some of the reasons are because the boat is of a certain age. I am trying to think of a good reason someone would change them other than the fact that they have a crack in them. I mean, cracking a riser or manifolds is hard isn't it? Do they clog up and this is something that I was never aware of? I mean if they clog up, you would notice if water wasn't coming out your exhaust right? I was just curious, and thought someone might be able to clarify for me. Thanks

[sydneyACE]

They can crack very easily if the boat isn't winterized.
The water sits in them and when it freezes, the manifolds crack along the bottom edges.
I swapped a motor for a guy who forgot to winterize. We were able to braze the cracks and repair them successfuly.

If a boat has been run a lot in the salt water, the inside water jacket eventually corrodes away.
I had to relpace the risers on my boat when I first got it because they were really bad from corrosion and had freeze cracks as well.
http://i36.photobucket.com/albums/e9/sydneyACE/Supras/SDC10459.jpg
http://i36.photobucket.com/albums/e9/sydneyACE/Supras/SDC10477.jpg

As far as replacing them after a certain age, I think that some people are probably wasting money.
If anyone HAS replaced theirs because of age and not because of a specific failure, please send them to me! :)
IMO, because of how much those cost, you shouldn't replace them until they have a failure.
A whole set would be what? About $1,100?
That's not preventative maintenance IMO.

[sydneyACE]

http://i36.photobucket.com/albums/e9/sydneyACE/Supras/SDC10469.jpg

[haugy]

As Travis stated, if properly cared for they should last a very long time. In my 89 Comp, 90 Mariah, and 90 Saltare I've never had to or been close to needing new risers or manifolds.

If they ever got bad enough, I may repaint them, that's about it. Other than making sure the gaskets are good they shouldn't need replacing or work.

[suprasam]

Dang Travis, did you pull those out from under the Titanic? My boat was in salt water at some point in its life, and I have no idea knowing how well the flushed or if they did. The motor doesn't over heat, but looking at that scares the crap out of me. When I pulled some other parts, I could see some rust...but nothing major. Should I pull mine to check and see if they are bad ? I wasnt worried till now.

[foxriverat]

Just replaced manifold and riser gaskets on my 96 comp yesterday. Everything looked good inside.