What size piston to buy?

[oic0]

I can buy my own piston for ~$60 cheaper than the plating service will sell me one, but size which one do I buy? I'm new to the plated cylinder thing. Since they add material and the actual cylinder isn't worn down, do I just buy the same size as I had? My bore isn't damaged, just getting shiny around the exhaust port.
*note* yes thats black paint like stuff, its all inside my intake tract and ports. No I don't know why or who did it, maybe thermal insulation for the intake charge or something? who knows*

[Roostmad1]

yes go for standard size,before you put your new piston and rings in scotch brite the cylinder liner to take any glaze of so the rings will seat in properly,but when you do it make sure its in a criss cross pattern,goodluck

[B2]

In the consensus of the group, does the cylinder even need replating?  The cross hatch is visible and does not appear to be flaking. 

I am working on a bike that had a loose exhaust which caused dirt to get sucked into the cylinder.  Looking through the exhaust port, it has vertical striations on the cylinder wall.  I thought I would Scotchbrite it in a crosshatch and see how it looked afterward.  If it appears okay and the piston looks good, why not just re-ring it and run it?  Thanks, Kenny

[oic0]

B2, I don't know. Someone told me it looked like the plating was starting to wear away at the exhaust port? I'm new to the plating thing, ive always had sleeves so I'm a total noob to this.

[bigbellybob]

I can buy my own piston for ~$60 cheaper than the plating service will sell me one, but size which one do I buy?

just another reason why its not to bad to get the piston from the platter. like i said in you other thread they will need the piston to size the bore correctly if you send them an over size piston the jug will get set up for that piston. IMO get the standard size.


I also don?t break the glaze on my cylinder. New rings in the shiny bore tell its time for a replate. And it always seals back up just fine. Didn?t Stewart test deglazed against non-deglased bores sometime back?

[oic0]

Just to verify, it does look like it needs plating right? from the shinyness? (hard to see in the first pictures, but in the third and in person, around the exhaust port is shiny)

[meangreen500]

mine looked like that I took it to a friend we gave it a quick hone and it looked great. I did get the .5 mm over size and have been running it for a while. I wouldnt spend the money on that cylinder unless the chrome comes off in small chunks or is out of round.  

[oic0]

I guess I'll just throw it back together and ride then after I get the mud out of it. Bought some kerosene. Going to fill the bottom end with that. work it all around, flush it, repeat, etc... When it was together it made a little over 165psi compression.
Already cleaned up the reeds and cylinder. Need to do the carb and bottom end, then find the airbox problem that let this happen in the first place! (soon as I get that bird nest out of there, I feel bad though, it has eggs )

[cbxracer30]

The black "paint" inside the transfers & intake is a factory coating they all come with , it will come off and isn't hurting anything.CBX

[oic0]

Guess that means my cylinder must be on the original plating.

Found the culprit that caused the mud ingestion. The plastic ring that clamps the filter rubber tube to the air box was warped, also someone put it back together with a thick washer on only one bolt.... Ordered a new one and also when I put it back together I'm going to use silicone for peace of mind.

Before I start putting it back together, everyone agrees the bore looks safe?
How thick is this plating stuff anyway? Like in my last picture up there in the exhaust port where you can see two colors where its cut away for the port, is the darker color how thick the plating is? is it really that thick?

[cbxracer30]

You should have someone run a hone through it , this should take away the discoloration .CBX

[dave916]

B2, I don't know. Someone told me it looked like the plating was starting to wear away at the exhaust port? I'm new to the plating thing, ive always had sleeves so I'm a total noob to this.

not sure if that it is the pic but it look like there could be a crack  between the RH exhaust subports
may also want to check the kips valves  as the centre valve looks very much to one side
if the barrel is worn you would usual find a lip about 10mm from TDC [where the rings stop] will be worse on exhaust side
not sure if you have seen this http://www.hallbergs.net/kx500/

[oic0]

Yeah the kips rattles all over the place. I rotated the pins and it helped some. Its still noisy though. Tempted to have it welded.  When its out I can't see anything physically wrong with it or worn, not in its place in the cylinder either.

[tschisi]

I?ve got a similar question.
I?m not planning to re-plate my cylinder or change my piston because both surfaces look fine and the bike ran good.
But i measured the gap between cylinder and piston with a feeler gauge like this:
http://img690.imageshack.us/img690/6742/gapu.jpg
(maybe not meaningful, i know) and it is 0,15mm.
Could that be ok?

[oic0]

I'm a noob too but I think you're measuring at the wrong end . I gave up on trying to measure mine and figured if its making good compression and the skirt isn't beat up then its probably alright.