Blown Head Gasket....WHY?

[chris650]

Hello experts! So im trying to solve an issue. Recently replaced a blown head gasket on a 260 mercruiser. There was water intrusion in cylinder #6, which you will see by the pics, caused most of the damage which is on the exhaust side of the gasket. So obviously, water was on top of the piston causing immence pressure. But my dilema is...what caused the initial damage? After getting the new gasket on, i noticed that the starboard side ex manifold was apprx 40 degrees hotter than the port side. Had both manifolds off and they tested fine. Any suggestions or ideas on my issue? I dont want another gasket to blow on my buddy. Thx!

 

[alldodge]

Recently replaced a blown head gasket on a 260 mercruiser

The 40 degrees difference had no effect on re-blowing the head gasket. The most probable cause is the head had some warpage. Did you check or have the head and block checked for flatness?

 

[chris650]

Yes. The decks checked out.

 

[chris650]

Im beginning to float the idea that either the gasket was compromised from the get-go, or even damaged during the rebuild. Is that a far fetched possibility? Thing is, he said the boat ran fine for awhile.

 

[alldodge]

Gaskets blow most often from overheat and the head warps. Can also happen from fatigue, but this doesn't happen very often. For it to happen not very long after replaced, and with flatness (for V8 cast iron) should be no more then .006 and even that much I would like to see no more then .004

If gasket was damaged then yes that to could be the issue

 

[chris650]

Is it a possibility that whoever rebuilt the engine over tightened the head bolts?

 

[alldodge]

Over torque usually causes bolt to fail and then the head. If the bolts where not torque in amount of passes and sequence, then this can cause a warp

 

[Scott Danforth]

what caused your initial water intrusion. if it was the manifolds, inspect for bad gasket surfaces or cracks. if you find a crack, throw away your manifolds and elbows and buy new.

 

[Lou C]

Also not really cleaning out the cyl head bolt holes in the block, can cause the bolts to feel tight when the actual clamping force is not what it should be. The holes have to be cleaned out thoroughly with solvent, compressed air and cleaned with a thread chaser. If the old bolts have a lot of corrosion on the threads that can't be cleaned up they should be replaced with new. Even my old block which had one bad overheat was flat to less than .003" on the deck surfaces.

 

[chris650]

Both manifolds, risers and elbows were takin off and pressure tested.

 

[chris650]

Interesting case....did the head gasket blow first CAUSING the water intrusion into the cylinder? Or visa-versa. Also interesting the location where it blew. If head was warped id be more inclined to think that the crush would have more likely happened in between the cylinders. Though I could be wrong about that. What about the possibility of a restriction at the y pipe? A pc of and old water shutter perhaps? Causing back pressure.