Top End Wear results

Dec 29, 2002
I've had my KDX200 for about 3 years now. In Jan 02, I did a top end job and put in a Pro-X piston and rings. I measured the ring gap and all that and wrote it down in my shop manual. Cleaned a BUNCH of carbon off the KIPS main valve (you can see the pictures in the "Tech section". Today, I took the top end off again, to see what what going on in there. Oil used was Yamalube 2R at 32:1 and my jetting is a little on the rich side. I ride several times a month for about 600 miles/year (according to my Trail Tech speedo....).

Here's what I found:

1) ring gap of new rings: 1/02 = .305 mm, 2/04 = .425 mm. Service limit = .650 mm. The rings wore .120 mm, and the difference between new and the limit is .345 mm. .120 is just over 1/3 of the service limit. I basically could've gone about 5 years between rings instead of 2, providing that wear stayed the same.

2) the piston, a Pro-X "A" size measured as new.

3) Although the ring wear wasn't much, there was enough carbon build-up on the KIPS main valve to make the teardown worthwhile, IMHO. I had to scrape some carbon off the exhaust port before I could pull the main valve out and one of the sub-valves didn't want to come out because of carbon on it.

4) there was just a little bit of carbon on the piston crown, and the piston itself looked great. With a Pro-X in one hand and a stock OEM piston in the other, there are some obvious differences. The Pro-X port is larger and rounded and the oil holes are smaller. The OEM has a smaller and sharper edged port and the oil holes are a little larger with beveled edges.

I could probably just stick the current piston back in and keep running it, but it's an "A" piston and my cylinder is a "B". I have a new OEM "B" piston in hand, so I'm going to run that instead. In the future, I'll probably plan on tearing down the top end every 2 years, installing new rings, and cleaning the KIPS.