125-200cc Cylinder Seized, What Caused This And How To Treat The Cylinder?

I know that it's a known problem for cylinders like these to seize on the exhaust bridge, the thing im more concerned about are the marks on the intake side of the cylinder. What could've been the thing causing those? Is it just the fact that the engine was running too hot/lean or could there also be a more specific reason? Also, is there something I should do to the cylinder before installing it again? I cant feel the marks with my nail at all so if I've understood correctly the cylinder should still be good to use? All help is appreciated.

I just bought the bike so I'm not sure about the old pistons size but the current piston is a B size. Not sure about the ring gap either but don't think that's the problem either. And yes there were 2 small holes drilled on the piston on the exhaust side. Is the black mark on the cylinder piston coating and if so I've heard that you should ve able to clean it off somehow correct?

there is an entire procedure for setting the "squish" which sets the correct compression, if you raise or lower it, increase or decrease you timing curve, increase or decrease your fuel oil ratio all these things can change the performance as well as heat transfer in your cylinder
since you said you recently acquired it, go stock on all settings then tune from there, baseline is always a good starting point

Thanks for the reply. I'm pretty sure that the piston was one from Vertex. I literally just bought the bike used for cheap and knew that the piston was most likely ready to be changed. That being said, I haven't really had a chance to look at the squish or anything like that. I mainly just wanted the information on how to prevent this happening in the future.
While taking off the cylinder I also noticed that the exhaust metal gasket had a piece broken off of it. Pretty sure the piece would've just flown out of the exhaust, and there shouldn't be a way for it to have ended up in the cylinder though, correct?

Thanks for the advice, I'll have to take a look at the whole procedure of measuring the squish as I'm not too familiar with it. I know how to tune a carb tho so that shouldn't be a problem.

Clean the bore with muriatic acid on a paper towel (swimming pool acid). If any aluminum has been transferred from the piston to the bore, this acid will dissolve it out of the bore surface. Muriatic acid dissolves aluminum but not the Nikasil bore surface.

Then clean with soap and water and a green scotchbrite.

Do not hone this cylinder. Nikasil should only be honed professionally with a diamond hone. Clean it with scotchbrite and leave it alone.

Notice how the blowby marks line up with all the port bridges? I've seen this on super high hour bikes when the ring finally starts losing its surface coating. I'd love to get that ring in my hands for inspection.

OK FINE!! (jk) Technically, yes, you can use an AO ball hone to deglaze Nikasil. But here's why I said don't do it:

Brush Research is where I get all my hones. Unfortunately, I've only seen Brush Research really address this use in NON-ported Nikasil cylinders. If the Nikasil has any thin or potentially damaged spots, an AO hone should not be used. Port edges are the other problem. It is possible to chip the Nikasil from the edges. While Nikasil is "harder" than aluminum oxide, this a bonding problem not a hardness issue. And while deglazing MIGHT be OK, trying to resurface a damaged Nikasil surface is not OK. Sounds like you are doing it correctly for deglazing, using the proper AO material, with slow speeds, and under flow. Otherwise, you wouldn't have had the luck you have.

I was going to say CH goddess.

setting the squish is actually in the owners manual

A word of caution to anyone using muriatic (hydrochloric) acid or any other dilute acid. Please follow all safety instructions such as wearing acid resistant gloves, eye protection, etc. and use with extreme caution. Anything that can dissolve metal also burns bare skin. Dangerous stuff!