Gray sludge and grit in cylinder/ lost compression

[WTF in KY]

New member here. First post. I just put a new wossner piston and rings in my 98 kdx 220r. Ran beautiful then after around 6 hours/40 miles it instantly lost compression. I took cylinder back off and sludge crap and grit in cylinder. Exhaust side of rings are fried. I have FMF Gnarly woods pipe/ power core 2 slip on, boyeson power valve if anything jetting should be a tad rich. I will check to see exactly what jets are in there and let you all know. 36:1 premix. New rod bearing. I have pics I will post when I figure out how. Any suggestions on what might have happened? No loss of coolant. No blown head or base gasket. No head warpage. Water pump working fine as well. I have been riding 4 strokes for many years. First time I rebuilt a 2 stroke in 30 years.. oh yeah power valve is clean and seems to be working fine to. It would still run but good thing I shut er down. Cylinder measurements still in spec. Luckily no visible damage either. I suppose it could need replated. Friendly suggestions and advice are welcomed. Thanks in advance guys.

[Molly's 70]

How does your air filter look?

[WTF in KY]

Air filter is new and pre oiled

[SS109]

One of two things IME. It's either piston/cylinder metal or it's a bearing(s). Have you checked your rod play up and down? Also, rotate the crank by hand and try feel if the bearings aren't smooth.

A few other questions... did you file fit the rings when you installed them? Did you make sure you got the air filter seated correctly? Got any pics of the resulting damage and sludge?

[WTF in KY]

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[kdx633]

the seal between the air box and rubber boot(plenum) that slips over the rear of the carb can be suspect.Was the cylinder replated?if so did you clean it very good,like not a hint of discoloration on a white paper towel when wiped.Looks as if an abrasive was present when engine was re-assembled.Doesnt look like sand sized grit as that would have left gouges.

[WTF in KY]

?

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[WTF in KY]

Do I need to replate?

[SS109]

Hmm, plating doesn't look too bad from what I can see. It's the original electrofusion plating that Kawasaki used on their cylinders back then. Is there any chipping around the ports? Any scratches or anything your fingernail catches on or feels? Any shiny spots of pure aluminum through the plating?

[Molly's 70]

That cylinder looks way better than I would have imagined.

[pumpguy]

The roughness of the cylinder base joint face makes me think this may have been re-plated. That's how mine looked when I got it back from Millinneum. Also, the V shaped openings to the boost ports lead me to think they might have been worked on to improve air flow. Mine are totally flat bottomed.

[WTF in KY]

Personally I think it looks usable. Not perfect. Nothing fingernails catch on. Granted I don't have a $500 set of gauges, but it seems to be within specs. I have another new set of rings and ring gap is definitely within specs. I am surprised it's not damaged worse either. Because all that sludge and grit in crankcase from earlier pics was all over cylinder walls too. It wouldn't surprise me if it has been worked on for more performance. Kid I bought it from said his grandpa had a motorcycle shop and that he just rebuilt it.

[WTF in KY]

I think I am going to disassemble and clean powervalve assembly doublecheck jetting and put it back together. I put bike sideways and cleaned up crankcase really good already. I don't feel any vertical play in rod bearings or crank bearings. I just would like to know why this happened. I wasn't given the initials WTF at birth for no reason I guess. Lol.

[WTF in KY]

Also in case anybody was wondering I had been using Klotz Super techniplate at 36:1.

[Molly's 70]

Clean that sucker up & run it!

[KDXGarage]

Whatever those grains are on the sides of the crankshaft look like "bearing graters" / "bearing destroyers".

[WTF in KY]

I know they do right! I got that all cleaned out of there. Actually all back together and riding. We will see how it holds up.