Ok, I pulled the manifolds and risers from the motor in question, the riser gaskets seemed to be fine on both manifolds...no rust trails inside either manifold on the riser end. No appearant cracks in either manifold or either riser, however in 2 of the exhaust ports on one of the manifolds there are some pretty heavy rust stains. any one have any idea what could be wrong here? This throws me for a loop since I just had the heads reworked last June, and replaced both manifold and riser gaskets at the same time

same manifold, different port

Exhaust valves not sealing properly thereby sucking water on intake stroke.

BT

do a Leakdown ...

....well, plled the plugs and they looked fine, although there is definately rust stains in the #2 and #4 exhaust ports in the head.


I was told by a very experienced mechanic (although not with marine engines) that if any silicone or sealer was used on an intake manifold gasket of a SBC that it would more than likely leak.......is there any truth to this?? if so, that may be my problem...

I would think the plugs would be cleaned if it was an intake gasket or milky oil. I do not like to use silicone on intakes on any motor. Only on the ends of the valley cover. Not much help sorry.