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Rebuilding top end and noticed some very slight surface rust on the cylinder walls. There's no texture or pitting from the rust, mostly discoloration. Wondering if I need to have it plated or if there's something I could do. I would upload pictures, but not really sure how.

Any advice would be greatly appreciated.

Thanks

I had the same thing after disassembling my 86 kdx200. I would take a green scotch bright pad and some pb blaster or liquid wrench and scrub her down. She may end up shiny as new. Only after doing this, did I realize that the plating inside the cylinder was in better shape than I thought. I would also do a quick soak spray afterward, coating the whole cylinder wall in your flavor lube of choice of it will be sitting. I do this every couple days, and will be until I put the cylinder back together. Hope this helps. Also look very closely at the edges of the plating around all the port holes, you may notice what no plating vs good plating is. I had a 2mm x 2mm spot near one port where the plating is worn, not a gouge, just worn,and it is toward the bottom, so I'm running it. I paid less for the bike than the cost to replate.

You may only want to do the soak spray if the cylinder is removed from the bottom end, not sure you want penetrating oil sitting in the bottom end.

Good idea nedrowjoe, I'll give er a scrubbin and see if that clears it up. Seems like that should be enough. And yeah shes off the bottom end, working on cleaning the KIPS right now.

Thanks for the help!

I have never seen anything like you describe, but I really don't think its rust as in iron oxide. The cylinder is aluminum with an electrofusion or Nikisil coating.

I would think what you are seeing is combustion by-products deposited in the cylinder's coating porosity.

I would be more concerned with the surface finish and the bore diameter. Take some measurements of the bore in several places and compare the measurements with published limits, and then maybe take a Scotch Brite pad to try to clean up the bore's surface, and see what you've got.

How's the piston? If scored or worn, it may be best to fit a new piston and get a re-plate.

What bike are you asking about?

Did a little work with the scotch pad and it took everything off except a very slight tint of tan. Piston looks almost new, but i have a new one going in anyways. I'll go take some measurement and get back.
Its an 03 kdx220.

I hope it's a aftermarket piston, the oem ones have a tendency to crack!

jjavaman wrote:I hope it's a aftermarket piston, the oem ones have a tendency to crack!

Yeah, Wiseco.