Re: 1989 Mercury 115 "Tower of Power" Sparkplug issue
Not Good, it's sucking water into the cylinder. What you see is emulsified oil/fuel/water mixture.
If it's only in #6 cylinder, most likely the crankshaft lower seals are bad. But it's also possible the exhaust cover/baffle/inner cover could be leaking/spraying into the #6 cylinder's exhaust ports.
Since you'll have to pull the powerhead for either repair, I'd recommend removing the lower bearing cap/seal carrier first, for inspection. If you find a bad pair of crank seals (and it'll be Most Obvious if they're bad!), you've likely found the problem and no further disassembly may be required.
If, however, the crank seals don't really look all that bad, it'd be a good idea to remove the exhaust manifold outer cover, inspect the baffle plate, and check for internal leaks.
Another good clue to the source of the problem, if the manifold is leaking water, all the carbon buildup in the area of #6 exhaust ports will be washed away. If the exhaust area is clean or just normal carbon-y looking, it's almost certain that the seals are the only source of your problem.
If you'll check a recent thread I posted in, you'll find a complete dissertation on fixing exhaust-side water leaks, if it comes to that.
Otherwise, it's a simple R&R of the powerhead and <relatively> simple R&R of the bearing carrier for seal replacement. You'll need the following parts for that job:
Powerhead base gasket, 1 ea;
Crankshaft oil seals, 2 ea;
"End Cap" (bearing/seal carrier) O-ring.
Use extreme caution when removing bolts, if they don't readily break free with normal force, you need to use heat, vibration (shock), and penetrant as required to bust the bolts loose. If the bolt truly is stuck and absolutely won't come out no matter what you do, don't twist off the bolt head, drill it out.
Hopefully your motor isn't too salty, and it'll come apart without a lot of drama.
Note that you don't need to split the crankcase open to pull the lower bearing end cap; it's a 'snug' but not press-fit; after removing the 3 bolts holding it to the block, you can use a puller with appropriate bolts and pull it right out. Just use caution if putting stress on the end cap mounting tabs, it's possible to break them if you're prying/pushing too hard on them.
HTH & keep us posted on your progresss.........ed
p.s. it'd be a good idea to spray some WD or other water-displacing lubricant into the cylinders to prevent any corrosion from the water-mix.
