SCORPIO
Well-Known Member
I pulled the risers off my boat last night. These engines are both new crate motors. The port was replaced spring 2015 and the starboard in August of 2016. They both have closed cooling half systems, meaning the risers and manifolds see salt water. The port engine has Mercruiser manifolds and risers and the starboard has Barr units. I found quite a bit of surface rust in three of the exhaust manifolds! No valve damage and no bore damage confirmed using a bore scope in all the spark plug holes and exhaust ports. Looks like the riser gaskets must have leaked and let some water into the exhaust manifolds. The gaskets all looked intact and the water passages all appeared to be in decent shape, only surface corrosion, no scale or clogging or flaking rust. If I had run those another season without inspecting, I could have lost one or both engines. Since I cannot confirm the riser gasket seeping, I ordered all new Mercruiser manifolds and risers for both engines. The piece of mind is worth the cost. I'll scrap the old units and move on. My plan going forward is to pull the risers EVERY YEAR and inspect and replace gaskets. I thought I was well withing spec pulling after two and three years respectively but that doesn't seem to be the case. BTW I did retorque the risers and manifolds after the first hour and then again at ten hours so that wasn't an issue.