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blackhawk
06-26-2002, 04:06 PM
I was reading another post and it got me thinking. Someone stated that they had ring wear and valve damage because of a bad riser gasket.

I am a moron when it comes to marine exhaust(how it works anyway). So, basically when a riser gasket goes water can go into your motor? How do you know if you have a bad riser gasket? I mean, if you can't tell how do you know it's bad. Is there water in the oil? Does it run hot? Run rough? Is there any tell tale signs? :confused:

MOP
06-26-2002, 06:11 PM
Some will not agree with me but being an old hard head marine Mech, If it shows rust stains on the out side change them. Clean surfaces well, if they look a little narrow from corrosion replace the elbow and carefully inspect manifolds. The elbows do deteriorate at a much faster rate because the tails and riser part dries and corrodes. The manifolds will last longer as they stay full. Fresh water boats get really great time out of them. In SALT they need changing much more frequently. What I have observed over many years risers 4 years manifolds 5-6 most guys bite the bullet and change the whole works, which I feel is the best way. But no matter fresh or salt the riser gaskets seem to get weepy they should be checked for tightness and leakage everytime you look over the engine. And like I said above if there is any doubt change them, gee if you do it your self it costs about 10-12 $$! And please us a very good quality Marine gasket compound. Some really trusted automotive stuff turns white and crusty and will let you down. Also cris cross tighten to make absolutely sure the mating surfaces contact evenly, if they leak they can ruin a really nice engine.

RickR
06-26-2002, 08:54 PM
Some late model Merc risers are stainless (1995) but the manifolds are still cast iron. I'm not sure about the new 496s.

I use Prematex "Hylomar" Sealant on almost all gaskets. The stuff is AMAZING. High Temp and will not harden.

When I bought the my 1995 454 Mag in 2000 the gaskets had already failed the caused the damage. I noticed the problem a few months later when I started getting excessive steam out of the exhaust.

If possible throw the manifolds away and get some "Stainless Marine" exhaust. :D :D :D

blackhawk
06-27-2002, 10:27 AM
Okay, now I am going to be a paranoid nervous wreck! I am not having any problems that I know of but that's what scares me. How do you know? My motor is a 1995 502 EFI with 180 hours. Wouldn't you get some water in the oil? Should I replace the gaskets just to be safe? Is it just the riser gaskets or the actual manifold gaskets that can go bad too?

David Ochs
06-27-2002, 10:38 AM
I don't know the technical reason for this. I had a new two ton gas engine International truck that developed burnt valves as a result of an exhaust leak. The leak was apparantly between the cylinder head and the exhaust manifold. This happened with only a couple of thousand miles on it.