do i fit expander ring on my new piston with new barrel or not

Eh?

I'd hope that if you were fitting a brand new barrel, you'd treat it to a new piston and ring set at the same time.

yes but do i need the expander ring it came with the new rings

You normally get (on a four stroke) two compression rings and an oil scraper ring - this is sometimes made up of two very thin rings with a springy bit in the middle like this from a Kwak ...





the rings often have a number or letter stamped on one face near to the gap - this usually has to be fitted facing upwards, but check for your bike.

its a two stroke the sprung wire is supposed to go under the second ring but its a bit tight for the barrel which concerns me any ideas

Ah, not seen that before but I've only dealt with pre 80's two strokes. What bike is it? I'd guess if the maker puts one in then it should be used. Have you checked the ring gap in the bore, sometimes it's necessary to file new rings down a bit to get the correct gap.

its a yamaha dt 50 im putting a big bore 60 kit on the old piston didnt have one but in the haynes the dt 80 has one its called an expander but with that on the second ring ill have to allow for it when i sought the gaps outits just getting a bit confusing any suggestions