Deburring inside of cylinder

I do this with .049 cylinders with a 80% success rate. Source a piece of tubing that fits fairly snug into the inside of the piston. If it's too loose, wrap tape around the tubing and force it into the underside of the piston. Take the piston and tubing and insert it upside down in the cylinder. Use Mothers Polishing compound or similar and pull the piston up to the point it begins to bind. Place a Q-tip full of Mothers into the the exhaust port and twirl. Don't be aggressive as it will jam the piston in the cylinder. Twirl the tubing while moving it slightly up and down. Eventually the burr will subside and allow the piston to come up higher in the bore. If the burr is very large, initially removing it can be done with a X-acto carefully using a jewelers loop to see it. Wash with hot soapy water to remove all traces of compound. I have used other forms of polishes and grits to speed this up if needed. Currently, if I have a problematic cylinder that won't tolerate finer compounds to fix, I use rottenstone mixed with oil and make it into a paste. Brasso works but is less aggressive . Powdered cleanser like Ajax works but you have to be very careful not to get carried away.