Diagnosing bad manifold to riser gasket?

[JaCrispy]

1988 260/5.7 Merc.

Developed hydro lock mid season, was able to bump the engine enough to get it running and out on the water never had an issue. Just when I went to restart for the next trip a week or two later.

Seems to be #4 cylinder which is 2nd in on stbd side only.

When I brought the boat back to my shop for winter, I tried starting it, no go. Pulling #4 plug the boat cranked and water shot out.

I pulled the riser and found water in the bottom of the manifold (only forward of the cast wall separating #4 and #6 cylinders), water in the head above the valve and in the cylinder.

Pulled the manifold and tried a gravity feed wet test, no leaks. Made a block off plate and pressurized the waterjacket with air, no leaks.

Looked at the mounting surface between the riser and manifold and hard to tell if any leakage since I replaced the gaskets back in early spring. I also couldn't tell if there were any real traces of water marks leaking down inside the manifold.

Right now, I blew out the cylinder and exhaust port and poured water into the engine until it ran out the drive. Hoping...not really hoping, to see if water gets into the cylinder with the manifold/riser removed.

Any other tips?

 

[Bondo]

Looked at the mounting surface between the riser and manifold and hard to tell if any leakage since I replaced the gaskets back in early spring. I also couldn't tell if there were any real traces of water marks leaking down inside the manifold.

Ayuh,.... What gaskets did ya use,..??

Did ya clean the gasket surfaces of the riser, 'n manifold to Clean bare Metal,..??

I use a flat file to check 'em for bein' True,....

How wide are the flat gasket surfaces 'tween the water, 'n exhaust cavities,..??

Yer story leads me to believe this is where yer problem lies,...

 

[JaCrispy]

I used the stainless steel gasket with blue coating. I did run a file over the surfaces before reinstalling them. Off the top of my head, the the metal thickness is about 1/4 to 5/16".

Would a leak in the cylinder, head gasket or head be able to fill up the cavity in the manifold? It was full enough to run down towards the front cylinder.

 

[Bondo]

Ayuh,... I donno if a cracked head would have that much water or not,....

I use the Merc carbon metalic gaskets on dry,....

Only problem I've ever had was the GLM manifolds were machined low in the center gasket surface,...
Flattened 'em on a big belt sander at the machine shop,....
Still workin' so far,...

 

[Mercruiser420]

I would always do a cylinder leak down test first anytime I have engine problems/water leaks. Check the patient's pulse first, you dont want to perform a surgery on a dead patient. A compression test will provide some good info (if any damage was done). Any bent push rods? Valves can freeze in their guides from the water leaking onto them which will bend pushrods. Remember water goes through 1 block, 2 heads, 2 manifolds and 2 risers. Although unlikely it is possible that its having multiple leaks, in 1 or 2 or 4 of those 7 components. You definitely want to make sure the engine is tight n healthy before you start spending time on cooling/exhaust. Good luck

 

[JaCrispy]

Well I've had the engine full of water, full enough to run out of the port riser and out the drive, for 2 days and no water in the cylinder(s). I'm going to call it a riser gasket/surface failure. I have a 6" woodworking belt sander at home, going to hit those mating surfaces, install a new gasket and run it on muffs a while.