Discoloration on piston and sleeve
 

I wouldn't be too concerned with it. The color is about what you'd want. If it were black, it would have been run lean. If the engine runs good, I wouldn't worry about it.

The problem is the engine was sold and the buyer claims it does not run. It ran 5 months prior to the sale when I stored it away. I pinched the fuel line, used after run oil and kept it the same way I did years prior. Over the time I had it I used Traxxas brand fuel and typically ran it on the richer side...

Then the buyer doesn't know what he's doing. Unless the piston/liner fit is bad, it should run. By the looks of the picture, it doesn't look like it was run that much.

http://www.rcuniverse.com/forum/atta...mentid=2133641
This picture was also sent with saying it was hard to turn over by hand. The piston is at two different heights in the picture, but it is seized? Here is what the buyer is saying.
" There is putting in the piston and scorching on the cylinder walls and its seized in the sleeve. That is common for an improperly tuned and ruined motor. I'm a master mechanic of 20 years and understand how engines work as well I own a 1200 hp methanol injected BBF running 10% nitro. I understand as well have a degree don't play bs with meZ I've given you a fair chance tomorrow I will send along my statement from the Hoppy store as well my personal expert analysis. Fact is it doesn't work!"

If this is the case, wouldn't we see more signs of over the metal being over heated and carbonized fuel? Also, I would think a weaker component/ connection would break first. This spot being the connecting rod and most likely around the wrist pin.

Our ABC hobby engines are not built the same way as a 1200hp BBF. They use ring less aluminum Pistons in a tapered chrome plated bore. The bore is narrower at the top, thus the shiny chrome around the top of the inside of the cylinder. It sounds to me like the engine is gummed up from sitting and needs a squirt of fuel in the engine to loosen it up. It sounds to me like the guy is trying to screw you around.

If you sold it on eBay and were paid through PayPal, you might get screwed. I don't know what would be better - sorting it out as it is now or giving the guy a full refund and getting the truck back. It's obvious to me the guy is a douche and doesn't know what he's doing - and those guys are the ones that always "get something for nothing" because PayPal always sides with the buyer.

I would refund his money and take the engine back. Then clean it, start it and resell it to someone who knows what they are doing. Selling USED engines on ebay is never a good idea. There are so many protections for the consumer that it handicaps the seller and gives the consumer who is dishonest, a way to get their money back which has led to much more defrauding of EBAY.
To me this looks like a normal liner for an RC engine. The top as 1Q said is shiny because they work on a pinch basis, so that just indicates that its pinching at the top as it should and shiny and clean is good. Its probably just gunked up with the after run oil and some leftover fuel oil. advise him to return the needles to factory resets and then flush it with Alcohol, make sure its then dried/evacuated thoroughly, then add several drops of oil to the cylinder before trying to introduce fuel and start it.