if your putting in a new set of rings or a new piston , you must hone the cylinder to break the glaze. This will put a nice crosshatch pattern in the cylinder walls. The crosshatch pattern will hold oil and help lubricate the piston and rings as the rings wear in to the cylinder.
To Hone a Yamaha YBR 125 cylinder is easy . Just stick the hone in the cylinder, add some oil and Move the hone back and forth in the cylinder to produce a cross hatch pattern and in a minute or so your done.
look after your stones , the biggest problems i see with this job is using old tired abused stones.
do not use your honer on Nikosil'ed barrels as it will damage your stones and will need replacing .
you can buy honing tool on Ebay UK here
or Amazon UK here .