I need a little help with a problem with my 525 efis with around 90 hours, in my 2005 42' EX. When I bought the boat we had to have the port motor top end rebuilt due to a bad #8 cylinder. The piston was damaged and the cylinder walls were scored. Never did find a definite answer to what caused the problem. Tested everything including the injectors, pressure tested the CMI headers, no obvious problems. Might have been caused by reversion?
Now the starboard engine #8 cylinder has the same problem. Damaged piston and definite water reversion. We did find a broken/cracked ceramic on the spark plug on this one. Maybe was not firing and sucked some water back. You can see a definite water track from the header port into the exhaust port on the head. Any ideas from anyone with similar problems?

Did you have the C.M.I exhaust pressure tested? Heard there was a weld problem in 05.

That's just what I was thinking, check the headers. Good luck.

Not just in 05 but every year they were made. They're terrible!! Def check the headers!! They leak all the time.

Headers, they all leak at the rear cylinders, some only leak warm and will really fool you.

Didn't think about them being warm and expanding and leaking. Makes sense, the mechanic pressure checked the set on the first engine before they put it back together. We had planned on checking these, too. If they leak when they are warm, then there really is no way to tell if the pressure test is okay.

did it break when you where comming down on the throttles??

I don't know when it broke. Never a problem, everything was normal, no lack of power. After we got back from the casino trip, my son who is a Harley mechanic was helping me clean it and flush the engines and while the hatch was open he said that the engine had a knocking noise in it. Sounded like it was coming from the back of the motor, and was not too loud. We went out the next day and when it was under a load you could tell it was worse. Cleaned the boat up again, flushed the motors and brought it over to CLPBS.

Do all headers exhibit this problem or just CMIs? I was thinking - do the Stellings have the same problems?

does not sound like the headers to me