496 mag exhaust manifold replacement
tricountytrail
Member Posts: 203 ✭✭
Had to pull one of my manifolds and riser on my 496 mag. It is a 2005 freshwater boat and has the aluminum manifolds and stainless steel risers. Just wondering what everyone's thoughts are. They were in great shape. Boat is new to me 2 years ago. Everything looks fine. I will pull The other risers at the end of season to check the exhaust flappers. I do not see any corrosion or anything they may have been replaced recently. The starters were both newer. What is everyone 's opinion on replacement? They are the dry joint and don't have any issues.
Comments
If inspections are good it's probably ok to keep it going although with the original manifold id probably replace with OEM preventively being nearly 20 years old. That's a expensive engine to replace. Yearly inspection, gasket replacement and re torque of bolt heads after the first reasons run would be be good practice.
Hard starts, loss of power, white smoke, change in sound while running are all signs of water intrusion in the manifold. @aero3113 can give a better description of it. He pays close attention to his motors so caught the issue in time to repair before costing him an engine.
I actually thought my batteries were bad. A couple seasons ago my port engine was cranking very slowly then it would start. Was good for the rest of the day till it sat and then would crank slowly. Turned out water was getting into the cylinders. I was very lucky I didn’t bend a rod. Beginning of this season I replaced my starboard risers and manifolds after I went to replace a manifold gasket. I didn’t like what I saw so preventative maintenance!
A few 10-12" of 3/8 all thread, maybe 3-4 of them makes getting the gasket and manifolds on without an extra set of hands.
Here is what I found out
by design, the engine management system will not provide spark to the plugs
until the engine has gone one revolution
They are designed to trap any condensation that might occur after engine shut down. By trapping this condensation it prevents any chances that the condensation can reach the iron valve seats/guides. this problem is seen more in the northern states where the water is much colder. It is more of a problem for people who keep there boats in the water. A proper idle down time before stopping the engine will help reduce the chance of this condensation from happening, They will do nothing to stop or prevent reversion.