Top-End Engine Rebuild Part 1: The Teardown
Updated: Sep 10, 2021
This Generation V 7.4L Mercruiser 454/Bravo 3 had a blown head gasket that was allowing a little bit of water into two starboard cylinders, causing a popping noise that occurred because water does not compress...so I started taking the motor apart.
At first it was thought a stuck exhaust valve was causing the rattle back through the carburetor, which could clearly be heard from the upper end of the motor while accelerating before repair. A compression test showing 30 psi in two cylinders on starboard bank confirmed a problem beyond exhaust flappers. At this point, I took the top end apart and discovered a blown head gasket. Both heads were removed to be re-manufactured by a local machine shop, which is what is recommended to alleviate this sort of issue.
Before Tear Down
Starboard Cylinder Bank (bad side)
Starboard Cylinder Head
Starboard Cylinder Head Removed
When going to the trouble of removing one head, it is prudent to do the other as it is not that much more in terms of cost and labor. Good thing it was done in this case, because it turned out this head gasket was warped (but not yet blown).
Port Cylinder Bank
With the condition of these original exhaust manifolds, it was wise to replace them.
Port Exhaust Manifold
Both cylinder heads and exhaust manifolds/risers removed from the engine. Things always get worse before they get better.