GT-40 exaust manifold??

[Wish]

1997 SN Ok, so I opened my motor box to change the oil and noticed little dime size and smaller pieces of rusted metal on the carpet under manifold. Looked under manifold and what I beleve to be part if it, has started to rust. Side and top of manifold seems to be ok other than what is some rust streaks between the PCM letters on the side of the manifolds like water has been dripping down it. But the metal rust falling off the underside concerns me. Whats the cause of the rust? (don't say water) Can it be slowed/stopped?? What am I in for???

[ski6jones]

Mine was like that from the previous owner. When i got the boat the packing was leaking profusely so I think that moisture in the bilge probably contributed to the rust on the manifold near the head. Also had signs of water on side of the manifolds as you mentioned.

 

I replaced the gaskets on the risers since they clearly had leaked or were leaking as evidence by the water residue. As I understand a leak at the riser can allow water to drip down into the exhaust ports on the head. Had to clean up the surface of the top of the manifold and bottom of the riser with a file. That fixed the leak at the riser.

 

I left the manifolds alone until i noticed one starting to leak, then ordered and replaced both. Main problem when replacing was corrosion on the bolts mounting the manifold to the head. Had to use an EZ out on a couple. That in itself might be a good reason to replace them now.

 

Skidim has the replacements. Don't remember the cost, I think around $3-400.

[Jody_Seal]

Florida Inboards has em too and they are a regular on this web site!

302/351-w manifolds $185.00 ( includes gaskets) each delivered in the lower 48!

Risers $75.00 (includes gaskets) each delivered in the lower 48!

floridainboards@msn.com

[Wish]

Can this cause internal issues? If so what would they be?. Not able to shell out that much right now but if it costs tons more down the road, I will. So what could it do??

[ski6jones]

Jody is certainly a better resource than I, but if your risers are leaking inside the manifold I think you can get water into the cylinders through the exhaust ports. I'd at least try to fix that. Buy some gaskets from Jody and seal up the risers properly.

 

My manifolds lasted several years with the exterior rust before they started to leak.

[Jody_Seal]

Provided you don't have a exhaust leak your manifolds will more than likely be ok even with the small amount of rust. But the problems start manifesting them selves when the dis assembly starts happening. Fasteners are galled, or rusted beyond being nice to while trying to take apart. splitting the manifold from the riser might and probably will break the fasteners and whats left will have to be extracted from the orifice. By the time all this is rectified and provided the manifolds are in usable shape and not all rusted up on the inside and after the time it took to nicely remove them you could be into the cost of new just by shop labor alone. Customers need not be around when We remove manifolds that are badly rusted and the fasteners are junk, We utilize a 10 pound sledge hammer for removal and there is a trick to doing it. 40 seconds and I can have them off and in the scrap pile!

[east tx skier]

I have never seen an inboard ski boat without rust on the underside of the exhaust manifolds. They will take a long time to rust through. You probably want to replace the riser gaskets though.

 

Be sure to prop up your motor box when the boat is not in use to provide some ventilation. Lots of condensation build up in that confined space. The condensation collects underneath the exhaust manifolds and goes to work.

 

Whatever you do, do not repaint them.