Inline 6, washed #6 plug - water jacket?

[blfink]

have a 1985 115 inline 6. It was a little underpowered lately, felt like it was only running on 5 (been there before). Put new plugs in, since they were a year old, thinking that would do the trick. It still acted the same. When I pulled the plugs I noticed #6 was clean with what looked like liquid spotting. Checked compression, all were same as last year except #6 which was about 7 psi lower (now at 130 psi). Talked to a guy at a local boat shop and he said it looked like the plug was washed with water. He said the inlines had a history of water jacket gasket leaks and causing such problems. My question is, does this sound right? If so, would replacing the gasket (assuming that is the problem) be enough or would I need to do something else because there was some water in the combustion area?

 

[AMD Rules]

Re: Inline 6, washed #6 plug - water jacket?

If it is just a little bit of moisture, its not that bad. If it is a lot.... it will be an indication that the lower crankshaft seal is failing and allowing water to enter the crankcase from below.

While the inlines do have a history of exhaust cover issues, you will find that water on #6 alone, is not likely a result of an exhaust cover failure. You'd expect to see moisture in more than one cylinder and normally higher up where they are more prone to crack from heat.

When the water jacket cover around the spark plug fails, it leaks water out to atmosphere, not inwards to the cylinder.

Prime suspect is the lip seal(s) on the crank shaft lower bearing cover. They're not extremely difficult to change, but the powerhead will need to come off to access them.