replace piston and rings without replating cylinder?

[moreccsthanlbs]

just curious, i have a 2000 kx500 with 500,000,000,000 hours on it still runs great, good compression, starts up 2nd kick every time, but it is starting to smoke a little bit. i'm guessin it could use a new set of rings just to freshin it up. i figure since i'm gonna be in there, i might as well put a new piston in also. do i need to have cylinder replated? if everything looks good can i just slap a new piston and rings in it? thanx in advance.
p.s..... or should i just leave it alone, like i said, it does run VERY strong still

[kaw rider]

check your compression first.

[Texas Champ.]

If it's smoking it the mix oil/fuel...on 2 stk. engines the rings don't control the crank case oil...that's in a seperate area of the motor...the only way you can get the bottom end oil into the top end is to have bad crank seals or the case to case seal is leaking...km

[KXcam22]

On my 92 I replaced the piston and rings after 14 years of service. Feel at the kick starter told the story and a compression test confirmed it.  The cylinder plating and KIPS wear was fine so all I needed was a piston and rings.  A visual inspection of the cylinder should show if the cylinder needs replating.  Tough bike. Cam.

[adrenalinejunky81]

New piston/rings is never a bad idea. Use some wd40 and a green scrubby to de-film the cylinder liner before installing, but as you probably already know, dont hone it. Just removing the carbon/oil residue is all thats needed if measurements are in spec. Giant piston=large surface area and less wear, probably a big reason 125s get rebuilt every season.

[hughes]

New piston/rings is never a bad idea. Use some wd40 and a green scrubby to de-film the cylinder liner before installing, but as you probably already know, dont hone it. Just removing the carbon/oil residue is all thats needed if measurements are in spec. Giant piston=large surface area and less wear, probably a big reason 125s get rebuilt every season.

There's nothing wrong with properly honing a plated cylinder. Cross hatch in the cylinder is used for oil retention. Honing is the best way to remove the oil glaze in the cylinder and any light scratches. Ball Hone is the preferred tool. Around 300 plus grit. Honing the cylinder is nothing hard to do but experience at doing it goes a long way. Key things for honing is proper sizing of the hone for the bore, grit, properly lubed when using, and speed at which you are turning the hone and the speed at which you move the hone up and down in the cylinder. You need to check for the plating to be worn away or chipped around the port edges. The cylinder would need to cleaned with soapy water and a rag after honing. I use contact cleaner after cleaning the cylinder with soapy water and then light coat of Yamalube 2R.

[moburki]

On my 92 I replaced the piston and rings after 14 years of service. Feel at the kick starter told the story and a compression test confirmed it.  The cylinder plating and KIPS wear was fine so all I needed was a piston and rings.  A visual inspection of the cylinder should show if the cylinder needs replating.  Tough bike. Cam.

I had similar reliability with mine. '95 KX5 ran flawlessly for 12 years without removing a head bolt. Still had plenty of power when I disassembled it. Only reason I had to rebuild was a leaking base gasket. Power valves (KIPS) were very, very gunked however. They were not doing their job. It does run better now with a fresh top end, and properly adjusted (and cleaned) KIPS. I did have to re-plate due to some questionable cylinder markings. Use the top end sticky above for minor port work and as a guide. Great info, and maybe a little extra kick for free! GL