TOPIC: Number 3 plug contamination ??

Pulled all but # 6 on my 1985 115 IL 6 Found grey metallic like contamination on the # plug All othres look ok.......What might this be ? Doesn't look like water and is not wet it flakes off.....

Picture

That is melted aluminum from the dome of the piston.
That can be caused by two things - detonation from too much timing or crummy fuel - OR - water intrusion.
Based on the rust I see on the two spark plugs I suspect water intrusion is your cause.
The inline-6 has a tendency to flex around a bit and consequently once in a while the inner water jacket either cracks or its gasket leaks water into the exhaust area where the water is sucked into the combustion chamber.
Under compression the water (H2O) turns into hydrogen and oxygen gases resulting in too much of these components added to the fuel & air mix coming in the carburetors and this causes and extremely lean and very hot condition and the aluminum piston domes begin to melt.
This splatter of aluminum on the plug is just an example of what had happened in that cylinder and it is most likely that other melted aluminum has transferred to the cylinder wall and may have also seized the rings on part of the piston. The compression reading might still be okay, but the piston is now running off center due to the rest of the rings still functioning, but the siezed area is allowing the piston skirt to rub against the cylinder wall and eventually catastrophic failure will occur unless the beast is disassembled and rescued now.
There are those among us that may suggest simply backing off the WOT timing and going to 40:1 and continue use of the beast as is, but I disagree and firmly believe now is the time to disassemble and rescue the beast before it is terminal and unrepairable.
I strongly encourage remachining the block at the inner watert jacket, remachining of the inner water jacket, and the relative remachining of the top edge of the block to maintain the specs rather than simply replacing the inner water jacket gasket.
There is a lot more to it so if you need further details - please write direct or ask & I will post a write-up.
You also need to carefully inspect for cracks between the water jackets and the exhaust ports, cracks in the inner water jacket itself, and cracks or corrosion caused pin holes in the baffle plate.
You will want to positively identify the cause of the melt-down before re-assembly or you're risking a lot of investment only to have the results re-occur.
Thom

Looks time consuming and expensive.

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This motor needs a teardown and full inspection.

Ewwwww, I hate it for you Don, that looks (and sounds) bad! Is that your "spare" motor, or the one on your GT-160???

Those darn plugs can speak volumes. Most of the time its helpful. But sometimes I wish they would just keep there damn mouth shut!
Conrad

Well - Well - Well - Three holes in the ground ! LOL !

Just a little humor to brighten my day

Thanks Dr_Frankenmerc for your input.... I suspected it was metal transfer when I saw it.

Know anybody that re-builds Mercs for free

The brown deposit in the pic appears to be rust but I did not see evidence of that condition, looks like oily deposits/discoloration.

Hang in there Don. I'm sure you will figure out the root cause and get it back on the water.

Hang in there Don. I'm sure you will figure out the root cause and get it back on the water.

The MINUTE saw the post, I saw the problem maybe, and was right too. Just do what the "Doc" said beforehere. I have "been the "Hole in One", on #3 too. Timing was cranked for good gas, rebuild my old XS1500 after I did the first, "Hole in one.. (#3) first! The wrench set me at 25 Degrees, thinking running the best gas. NOT! SECOND.."Hole in One, .."3rd "hole". Back again, after 15 minutes run time. Do like Thom says, (we both know, those.."little silver balls, a plug!? Find the cause if new, and yers aint. Gotta come apart to live, and all "external", (carbs/timing/fuel pumps, need a upgrade top "NOS"..GOOD. etc. Like Thom said, there IS water intrusion there too. And he .."kinda knows the old .."TOPS"!

Won't be using the motor any time soon......... I suspect a re-build is in order..........1985-2011.... 26 years is a long time, so not a real big surprise...

Still looks good on the outside !

Sorry to be blunt here , but to me it is yet another example of a motor being run with a number of things " wrong "

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as in timing / old fuel / water in fuel / wrong prop / partially plugged carburetor / old impeller / poor grade oil etc , etc.

it will be a good project. let me know if you need a piston or anything for it. Like Doc says comb through it now before anything else goes wrong with it. Inspect the cylinder wall be sure no scoring happened. I have a 90 that blew like this one on cyl # 3 and i was amazed that there was no cylinder damage. Just a little cleaning was in order. This is a good way to get to know your merc.

I know one thing. Thats one sharp looking BOAT! Like the color scheme! Good luck fixing the motor, and its happened too many us too. And sometimes better to catch a problem in time, than toast the block to unrepairable. Wish the best...