Top end parts evaluation




KTM xc-w 200, 2011, 130 hours. Use Motul, 50:1. Plug looked dark-brown and dry. Ran fine, just thought I would do the top for fun.

Assuming the pics attached can be seen, can someone tell me what this means? Lots of black on the piston top - Too lean? Too rich? The piston has a couple slight scratches, vertical, at the intake side. I can feel one with my nail. Head is clean.


Yea, it doesn't look bad. For sure need to re-coat the cylinder. You probably pulled in some dirt through the airbox at one point, which is why the cylinder got scratched up. It happens more often then not. But honestly, I've seen a lot worse coming out of running motors.

In terms of the black crud on the piston, that's pretty normal. It took me a long time of experimenting with different combo's AND riding styles to get rid of that "caking". It is very much related to how you ride the bike and how rich the jetting is. You can solve this through running a higher oil/fuel ratio, or leaning out the jetting sightly. I prefer a higher oil/fuel ratio because that won't do any damage. After you build the new motor, try 40:1 and keep checking the plug after every ride. It should be bright brown, not dark brown. The anode should also not change in color much, you should still be able to see silver shining through. You can also pop the tank off and look down the spark plug hole with a flashlight to see the piston and make sure its not getting dark.

I run a super fat 205 main on my 150SX because I run a 32:1 mixture. More oil = better sealing of the rings AND more lubrication in the bottom end = longer life. However, you still need to have ample fuel getting into the system, so its critical to have a "happy medium" of jetting AND oil mixture.

I would have it diamond honed first. I don't see anything too deep. I bet in would clean right up with a flex hone. I've done it many times to a nikasil the cylinder it will look new and the cross hatching will be correct. I don't think a replate is necessary. It looks like it is time for a refresh though. The piston shows a little blow by. I agree keeping the eye on the jetting once finished.

Edited by jim1234

Looks like you should change your piston more often. You run it that long, it starts banging around in the cylinder. Wear and even damage may occur. Toss a new piston in the hole nad run it again. Expect to change it sooner, maybe 40 hours. At that point you should see no additional wear so you will toss another piston in and run another 40 hours. Running them to the brink of destruction, even though it did not fail, does accelerate wear of the cylinder (which is the expensive part).

Edited by 1987CR250R


Edited by JRod4928

Looks pretty good, IMHO. I don't think you heed to hone nikasil, and at 130 hours, I don't think it would need replating unless the nikasil is gouged. You said the piston had scratches. Did you mean cylinder??

I would clean the cylinder with warm soap and water, scotchbrite it to get the glaze off and install a new piston kit in there.

My 05 200 is still out there (I know who bought it) still running great on the original nikasil plating with well over 500 hours on it. Not saying it doesn't need it, but saying it is not an issue unless it gets damaged.

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