Water leaking around exhaust manifold bolt

[mhinnc]

The exhaust manifold was replaced last year just after we bought the boat due to corrosion on the older manifold which left a small hole near the aft part of the manifold.

Previous to our ownership someone replaced each stud & nut with bolts. When the bolts were removed for us by a mechanic either at that time or earlier the bolts tips snapped.

The first and second bolts (left to right) snapped far enough in the head that enough threads were left to tighten them well. The third didn't fair that well and when tightening felt "soft", but tight enough to hold.

After putting about 5 hours of operating time on the engine since, a leak has started, where a small bit of water bubbles around the bolt head (pictured here).
What would be the better way of dealing with this?

[Dave Neptune]

Good to hear the pump was just an air pocket.

Do you have a lock washer on the bolt? They will leak out of the "split" if water is leaking to the bolt somewhere. Bolt torque could be a factor too.

MMI has an oversize stud set available. Then you could easily drill out the pieces that are snapped off, drill and tap the new threads and manifold and your good to go.

If you do have the lock washer leaking syndrome, carefully replacing with a flat or "star lock" should finish the season. Then do the above for a good quality fix that will last.

Dave Neptune

[mhinnc]

Dave, would you happen to know what, if any, problems might show up with water getting to the bolt? Or is the bolt normally exposed to water in the manifold? The manifold is from Moyer and shipped to us new last year.

[Dave Neptune]

As I recall the "studs" were exposed to the water jacket in the block. The "through-hole" for the studs are solid material with no exposure to water or the intake and exhaust runners. A big reason for studs is they can be sealed when installing easily not so with bolts going deep down a hole.

Dave Neptune