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Hello,

Started to put new rings in my top end today ('01 KDX200) and found that my piston was crack and the cylinder had some gouging. The odd thing was that 7 of the 8 bolts for the head had white corrosion on the shanks, but one was shiny new looking. I bought this bike in Aug. of '09 and am the second owner. The original owner said he never rebuilt the top end, but now I wonder. How can I tell if the cylinder has been worked on? Replated or sleeved? After cleaning the carbon off of the piston the only markings I could find was the letter "B" and and arrow. Is this a factory mark/piston? I also suspended a small magnet in the cylinder and it was attracted to the sides of the cylinder. Does this indicate that it has been sleeved?

Thanks
Sthutch

You should be able to see a distinct line around the cylinder on the top. also if you look close at the ports you may be able to see that they are not lined up prefect. The piston mark sounds like a stock piston. Got any pics?

Here are some pics

The scratches came after I removed the piston.




Note the nice shinny bolt at about the 3:00 position










Hope this helps.
Sthutch

Have it replated and a new piston.

A magnet would stick to the walls if it was sleeved.

Pardon my ignorance, but are sleeved cylinders also plated?

No...

Looks like that piston was a few revolutions short of grenading itself. Just in time.

the corrosion is fine mate, when aluminium and steel touch they pretty much raper eachother, next time you put it together put a little copper slip on them

doesnt look like you have a sleeve.

Agreed. That whole motor looks stock, and untouched, to me. No sleeve. Original piston. The cylinder doesn't look very bad to me either. It might just clean up and be fine.
I also agree with Nick, Just in time!
You will find that stock pistons are offered in A, B, C, and sometimes D sizes. This letter indicates a very slight (0.0001"?) difference in diameter - "A" being the smallest. When you by another one, look for a B or C.

check the inside for scratch and gouges, and see how big is the lip at the top of the cylinder where the ring are a the highest point.
Use a scotchbrite pad to deglaze the cylinder.

Looks to me like the plating is worn off on the skirts, and some of those gouges look to go all the way through. Not sure a scotchbright is gonna do much for it.

Not sleeved.

Needs a replate.

Most likely original piston, or is definitely OEM (Pro-X) replacement.

To get most of cyl, buy an "A" piston, and send with cyl for plating.

http://www.langcourt.com does a fantastic job.

I second langcourt. Fast turnaround, good pricing, and beautiful work!

you need to replate the cylinder,[if your going to run a stock replacement piston].. the piston [cast pistons] will [break off} or crack at the skirts like yours in the pick [lucky] from having to much clearence in the bore. the skirts on the piston is what is taking the most force, and the piston will litarely walk back and fourth in the bore......and will break the skirts......

if your plating isnt wore thru,[cant really tell from the pics] you can have you cylinder clearance checked. see how much clearance you have...and to make sure the bore is round"not egg shaped"..you might be able to run a forged "wiesco" and not have to replate. a forged piston swells when it heats up "normal opperating temp" so it needs more clearance than a stock or cast piston.

Agreed the bike will run without replating.
Also agreed that the cylinder DOES need replating.
The gouges will not clean up with scotch pads and the skirts
look to be worn through.
Do it right and be done with it........

Hello,

Thanks to all for their input. I am a real beginner when it comes to turning a wrenches and motors, but I am learning. You help is greatly appreciated! I will be ordering a new piston and then send out the cylinder for replating.

Thanks again,
Sthutch

sthutch wrote:Hello,

Thanks to all for their input. I am a real beginner when it comes to turning a wrenches and motors, but I am learning. You help is greatly appreciated! I will be ordering a new piston and then send out the cylinder for replating.

Thanks again,
Sthutch

Where do you live in Mi ?

I live in Sanford. It is about 5 miles west of Midland.

sthutch wrote:I live in Sanford. It is about 5 miles west of Midland.

You ride St.Helens or anywhere in that area ?

Merry Christmas!

For a local ride, Gladwin. Its way sandy in the south, but the northern loop is fun. I haven't ridden St. Helen. I ride the Leota and Denton Loops. I have seen the connector to St. Helen, but have not rode the eastern part of the state. I spend quite a bit of time about 20 miles west of Clare in the summer so I tend to ride the Evart/Tin Cup/Little Manistee Loops. How about you?