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can anybody tell me why or what would cause an exhaust valve to break? my buddy has a very mild cam, nothing extreme, roller rockers and pro topline heads this is the second time this has happened to him, and both been exhaust! any info would be apreiciated!

What kind of valves are they? If they are the ones that came with the heads, then they are probably just a standard grade stainless valve. The longevity of these valves in a performance marine environment would be sketchy. If you are planning to lean on the engine at all, or even like to do the extended 3800 - 4200 RPM cruises on a regular basis, then you would be well served to install a set of the inconel alloy valves by Manley, Ferea, et. al. Exhaust valves tend to get very hot in a marine engine due to the extreme loads these engines see.

Also, ensure that there is adequate valve to guide clearance. Double check the jetting on the engine to make sure it is not running lean. Lastly, pressure check the exhaust system to ensure that you are not leaking water back into the cylinder. Cold water hitting a red hot exhaust valve leads to premature failure of the valve in most cases.

Exactly.
And be sure you are running at least a 110gph fuel pump.

Was the stem bent like it hit the piston and then broke? Or was it a clean break? I was talking to somebody about this the other day. And recently they saw the same thing happen to a Ferrea inconel exhaust valve. I believe it is at Ferrea at this time being examined. Head broke off of the stem with no contact with the piston.

Also what Generation block is this? I had troubles with exhaust valves sticking in the guides when I changed heads on my GenV blocks. I had to plumb the back of the intake cause I kept taking out exhaust valves 6 and 8 cause they were overheating. No water was not flowing through the back of the block with the new heads.

One thing he said he did notice is that there was alot of steam coming out of the exhaust, he said before take off he checked the oil and there was no sign of water, and said his water temp was showing 150,but he does have a open cooling system, and rite after take off said the steam clear up, running 3300rpm and bam lost power! So with that being said maby due to a bad head gasket?

Head gasket could be a possibility, as would a leaking riser gasket or cracked manifold / riser. Was steam coming from just one side, or both? Sometimes it is not that uncommon to see a little steam in the exhaust, depending on weather conditions. Cooler air tends to show it more.

My gaskets were fine. It was just the head and Generation combo. It would take a valve out in 30 seconds once on plane. I had 2 identical engines and it only would happen on one engine. Water temps always read below 150*F, but temp is taken off the front of the intake. I also removed my water pump in place of a crossover.

Just drilling out the back of the intake took care of my problem.
Here is a thread chronicling my troubles.
http://forums.boatfreaks.org/showthr...t=piston+valve

Drilling out the back of the intake?

Lol, he says it always steams a little depending on water conditions. But he said it it looked like steam coming out of power plant!but once on plane for about 20-30sec it broke!

You drill out the back of the intake manifold into the the rear water jackets on the heads. Some aftermarket manifolds come like this and are plugged. I run the water straight into my exhaust manifolds or you can Tee it to the front of the intake. This propagates flow to the rear cylinders. It is illustrated in the link I put up.