Water entering lower cylinder

[Bluestream]

HI Guys,

I know this is a performance web site, but I'm at wits end with this issue.

I have a 89 Merc 9.9 That runs rough at idle and higher speeds. Lower plug looks wet/grey water emulsion and often small water droplets on.

Compression good at 105 PSI in both, gas is fresh and 50:1
New plugs installed, both getting good spark. (has aftermarket CDI box)
Carb (has carb from an 8HP) was taken apart and was spotless. Fuel needle/seat held pressure for 10 min, float set to 1 inch. Performed cylinder leak down test and results were good.


I have replaced the exhaust cover gaskets and they looked fine, but still same issue. (I could see water in lower cylinder with cover off) Exhaust baffle plate was warped a bit, but the bolts can pull it down tight. I used Loctite 518 on the surfaces to be sure, and still no better running. I removed powerhead and gaskets looked good. I used some Ultra Black around the drive shaft output area to make sure no water was getting in that area.

Is there any way for water from cooling system to enter the cylinder? I have heard lower seal can let water in, any truth to that?

Any advice appreciated, my next move is to part it out if I cant get it to run right

[rock]

Welcome to the site and yes, a bad lower seal can allow water to enter crankcase.

Rock

[Bluestream]

Thanks, I guess that has to be it, other than a cracked water jacket, I dont see any other way water can get in???

On this engine, the PTO crankshaft is hollow, and I can see right into the crankcase when I look in the shaft. I've never seen a design like this before. The crankshaft has an outer seal, such as any engine would have. And an inner seal that seals the drive shaft to the hollow output shaft. I assume the outer seal is the one that needs replacing? The inner seal looks like a rubber sleeve of a bunch of o-rings.