KDX200 Cylinder questions


16 replies to this topic
  • Sthutch

Posted December 22, 2010 - 05:32 PM

#1

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? Re-plated 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. :excuseme: Does this indicate that it has been sleeved?

Here are some pictures,

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Thanks
Sthutch

Edited by Sthutch, December 22, 2010 - 07:58 PM.
updating with pics


  • hobo99

Posted December 22, 2010 - 08:42 PM

#2

It looks like the piston is cast, not forged. Your cylinder will need a bore, its steel. As far as the crack...thats not good. at least it didn't shatter into pieces while you were ridding.

Im sure more KDX'r will chime in with more through answers

  • basketcasebill

Posted December 23, 2010 - 06:50 AM

#3

I'm not really seeing a sleeve in the crappy pictures, but with that groove you will need to decide to repair/replate or have a sleeve installed

the "B" indicates 65.95mm sizing as a "C" would be a 65.96mm

  • juliend

Posted December 23, 2010 - 07:37 AM

#4

It looks like the piston is cast, not forged. Your cylinder will need a bore, its steel. As far as the crack...thats not good. at least it didn't shatter into pieces while you were ridding.

Im sure more KDX'r will chime in with more through answers


That cylinder is plated, and in need of a re-plate. You can tell from the 3rd and 5th pictures that there is no liner installed.

  • Little Jeff

Posted December 23, 2010 - 09:53 AM

#5

Buy a new piston and send that with the Cylinder to Millinium Technologies for a replate. They can then hone the cylinder to the clearances required on the new piston. Had this done to my KDX 200 and they did a great job.
Jeff

  • hi_im_sean

Posted December 23, 2010 - 03:33 PM

#6

the stud corrosion thing is normal, my kdx's do the same thing, 1 or 2 stay new the rest corrode, has something to do with the coolant passages being so close or more likely they are the more exposed bolts when you wash it. just hit them with a wire brush, the trhreads never seem to be harmed, no pitting or anything on mine, check yours.

  • basketcasebill

Posted December 23, 2010 - 03:42 PM

#7

the stud corrosion thing is normal, my kdx's do the same thing, 1 or 2 stay new the rest corrode, has something to do with the coolant passages being so close or more likely they are the more exposed bolts when you wash it. just hit them with a wire brush, the trhreads never seem to be harmed, no pitting or anything on mine, check yours.


or maybee dielectric breakdown you know steel /aluminum/ steel they tend to not play well with one another:bonk:

  • ziegler408

Posted December 23, 2010 - 04:59 PM

#8

That's crystalization from the coolant...it's normal..def replate and send piston with, to ensure bore/piston gap, don't forget ring gap before putting rings on piston!

  • basketcasebill

Posted December 23, 2010 - 06:02 PM

#9

That's crystalization from the coolant...it's normal..def replate and send piston with, to ensure bore/piston gap, don't forget ring gap before putting rings on piston!


so explain why I see bolts come out like this in a 1970 honda mini trail 50, I cant seem to find where to put coolant in this thing

sorry but I think your wrong

  • juliend

Posted December 23, 2010 - 06:30 PM

#10

Agree with bill, not that the cause really matters anyway. The corrosion on the steel bolts is from being mated to aluminum. Coolant in and of itself would not cause such corrosion. Dissimilar metals however, will.

  • hi_im_sean

Posted December 23, 2010 - 06:39 PM

#11

or maybee dielectric breakdown you know steel /aluminum/ steel they tend to not play well with one another:bonk:


your right im such a retard for not remebering dialectric breakdown. :excuseme: me

  • basketcasebill

Posted December 23, 2010 - 06:48 PM

#12

your right im such a retard for not remebering dialectric breakdown. :excuseme: me


don't feel bad, although I knew what it was, I had to look up and make certain I spelled it right.

but next time it will cost you the kxd200

  • ziegler408

Posted December 23, 2010 - 07:10 PM

#13

Ohh ya...galvanic effect!!! Was thinking about another thread about cylinder jackrts crystalized...and for some dmb reason posted it here...doh!

  • Sthutch

Posted December 23, 2010 - 08:30 PM

#14

Hello,
Thanks for all the information! I am hoping to get the piston ordered the first of the week, and send them out.

Sthutch

  • KDXGarage

Posted December 25, 2010 - 09:03 AM

#15

Someone ran the bike for too many hours. KDX's are reliable, but they should not be ran until they break.

It is a plated cylinder. That is what worn, stock cylinders look like. It needs to be replated to be at its best. As you could tell before you took it apart, it would still run with the current condition and a new piston and rings. No need to do that, though. When you send it off for replating, see if they want a new piston to accompany it for best sizing.

That is the stock piston. Stock pistons have a letter stamped into them and an arrow.

The brown/black patches on the side mean ring blow-by. The rings were ran too long.
As far as the crack, most pistons will disintegrate at some point if one continues to run them. Runnign them causes stress and they can only withstand so much stress before they crack, then later the crack turns into a broken apart piston. This could be a few milliseconds later or weeks. Consider yourself lucky and get it replated and a new piston.

ALSO... make air filter cleaning and oiling a second religion for yourself.

If you feel up to great maintenance, do a pressure and vacuum test after the rebuild, then a compression test after break-in. Use the compression test as a baseline score to compare to future compression tests. It will let you know how things are weraing out in the cylinder.

Another also... clean and inspect the power valve parts. By looking at the piston, I assume someone let the power valves go for a while without a cleaning. Clean all the carbon off them.

KDXGarage... putting Americans to work since, like maybe 10 minutes ago. :excuseme:

  • Sthutch

Posted December 25, 2010 - 09:59 AM

#16

I have had the power valves soaking in mineral spirits to help loosen all the carbon. I have gotten most of it off, man was it a mess. What is the best way to clean the head. It has some build up on it also?

  • KDXGarage

Posted December 25, 2010 - 10:56 AM

#17

Go to the 22nd second and sing along.



DO NOT let it set for more than 10 minutes on aluminum parts. Rinse it off, dry the part and do another cycle.





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