92 KDX200 OEM Piston Rings

[SpruceItUp]

Hello all, me again haha. I bit the bullet and decided to buy new rings for my KDX. It has an OEM piston in it.

My question: Is the top ring different than the bottom? I bought a new set from Partzilla and when I went to take them out I noticed they are slightly different, with the R on the topside of the ring being different font than the other, and the edge of the ring for one of them was shiny while the other was dull.
When I tried to put the ring that was dull in the top slot, it got stuck and wouldn't move. I then put it in the bottom slot on the piston and it moved freely. The other ring moved freely in the top slot.
I just want to make sure this is correct before I put the bike back together, as the part numbers on Partzilla were the same for both rings.

Thanks!

[SpruceItUp]

Oh, one more thing, sorry I cannot provide pictures until sunday as I'm out of town until then. Sorry about that.

[KDXGarage]

What makes you think the piston is OEM? Just asking, that sounds kind of rough. Ha ha.

[SpruceItUp]

What makes you think the piston is OEM? Just asking, that sounds kind of rough. Ha ha.

You know what, I just realized I looked at the wrong piston online. For some reason I figured partzilla wouldn't have an actual picture, so I looked it up online and must've seen the wrong one, but it looks like the one I have.
Looks like I'm buying a piston! haha.
Found an OEM B size for $73 on ebay. Just gonna bite the bullet and buy it.

Man, I thought I was good at researching this sh*t!

Thanks,
Spruce

[billie_morini]

Spruce, are you talking about installing a cast piston? Cast pistons don't often perform well in KDX 200 / 220. They like to grenade. This is why most of us install a forged piston manufactured by Wössner or Wiseco.

[billie_morini]

Spruce, here's something that may interest you.
viewtopic.php?f=86&t=24789&p=213454#p213454

[SpruceItUp]

Spruce, here's something that may interest you.
viewtopic.php?f=86&t=24789&p=213454#p213454

Thanks for that!!
The piston I have is very similar, but isn't the same. If I remember, I'll upload photos when I get home.

[JimmyB]

Spruce, are you talking about installing a cast piston? Cast pistons don't often perform well in KDX 200 / 220. They like to grenade. This is why most of us install a forged piston manufactured by Wössner or Wiseco.

I know there was a problem with the OEM 220 pistons, was there a problem with the OEM 95+ 200 also? The 2 e-series(90-94) I had the OEM pistons ran forever, really good quality.

[billie_morini]

Spruce & Jimmy, two forum "authorities" clearly indicated in 2011 that KDX 200 cast piston is okay. I'm pasting a screenshot of their back-to-back posts herein.

Screenshot_20240824_154503_Free Adblocker Browser.jpg (259.24 KiB) Viewed 12453 times

[SpruceItUp]

Spruce & Jimmy, two forum "authorities" clearly indicated in 2011 that KDX 200 cast piston is okay. I'm pasting a screenshot of their back-to-back posts herein. Screenshot_20240824_154503_Free Adblocker Browser.jpg

I've heard that as well, but only for the 220. I figured I'm just going to return the rings and buy a Wiseco piston.

Figured I'm already pretty deep into this bike money-wise, whats a little more, yknow?

Thanks,
Spruce.

[KDXGarage]

Just KDX220R with piston concerns

[billie_morini]

Spruce, my preference for aftermarket forged pistons is Wössner. I was roadracing when Wiseco had too many quality control issues (not me, but fellow competitors suffered). Wössner has not incurred a similar experience.

A few years ago, Millennium re-coated my KDX 220 cylinder and mated up a standard sized Wössner piston for me. I also paid a few more bucks for them to check & adjust piston ring gaps and clean the power valves. Money well spent. Upon top end re-assembly in my garage, the renewed engine fired up on 1st kick!

[billie_morini]

KDX-G, Very pleased you'd weighed in because your knowledge about KDX is encyclopedic. Plus, you're a hecka nice guy.

[KDXGarage]

I am no encyclopedia. HA! I try to be nice, though.

Just reading in here helps one learn. I think I have been on forums for over 22 years, so I have read a alot.

[SpruceItUp]

Spruce, my preference for aftermarket forged pistons is Wössner. I was roadracing when Wiseco had too many quality control issues (not me, but fellow competitors suffered). Wössner has not incurred a similar experience.

A few years ago, Millennium re-coated my KDX 220 cylinder and mated up a standard sized Wössner piston for me. I also paid a few more bucks for them to check & adjust piston ring gaps and clean the power valves. Money well spent. Upon top end re-assembly in my garage, the renewed engine fired up on 1st kick!

Thanks for the info! Sadly I already ordered the Wiseco, but whenever I get the next piston I will definitely keep that in mind.

I am no encyclopedia. HA! I try to be nice, though.

Just reading in here helps one learn. I think I have been on forums for over 22 years, so I have read a alot.

And billie is right! Thanks for all your help, it's greatly appreciated

[SpruceItUp]

Sorry- I keep messing up the post somehow whenever I go to submit.

I finally got my new piston and rings (somehow was sent the wrong rings the first time) and I measured the ring gap from where it says in the manual (on the bottom of the cylinder) and got about 0.015" for both rings. The manual says it should be from 0.25 mm to 0.65mm, and 0.015" comes out to about 0.38mm. Does that sound good to run? Or is my cylinder worn out? Physically the plating looks fine, but I obviously don't have the tools to measure a cylinder lol.

I'm used to seeing about 0.012" on a 125, but this is a different bike so I figured I'd ask.

Thanks!

[KDXGarage]

I would take it to a machine shop and let them measure it.

Can you post a picture of the inside of the cylinder?

[SpruceItUp]

I would take it to a machine shop and let them measure it.

Can you post a picture of the inside of the cylinder?

I know it isn't perfect, but nothing can be felt with your fingernails. But I haven't worked with this plating before, so it's probably a good thing I'm getting a second opinion.

I hadn't seen before now on the bottom of the cylinder the plating might be worn where it changes to a slightly darker silver.

[KDXGarage]

I think you should get that measured at a machine shop. That looks kind of worn at the bottom (discoloration).

[Molly's 70]

Take your piston with you to the machine shop also.