I dough the pouring to much raw gas in the combustion chamber through the spark plug hole had nothing to do with it other than hydro locking up the piston. If you ran the saw with no mix for more than few seconds or minute then it may of over heated from lack of lubrication in the cylinders and cause the scoring at previous time. Basically you have fuel problem and probably wear problem from years of us. If you have never cleaned the carb since 94, it probably well over due cleaning and rebuild kit,

As for the replacement of the piston if the piston to bore clearance is within spec. the rings gap are within spec. and it easily move up and down with the plug out and builds compression within spec. I say it doing it job of going up and down and building compression. Now all you need it proper amount of fuel mist and correct timing of ignition.

If you want to prime the saw (which is what you attempted by pouring raw gas down the spark plug hole) please us Carb. cleaner in the spray can. The saw will fire off the carb. cleaner, you can control the amount going in the combustion chamber and it evaporates quicker than raw gas , and it does have some lubricating properties. IMO won't hurt as long as you don't run if over few seconds which is all it takes to start sucking mix through the carb. if it's not plugged up and not letting fuel reach the combustion chamber.

Thank you rcmoser for your kind reply.
The ring is definitely gone, so I have bought a new piston and head which I hope to install next week. I will put it back together and give it a quick go and if that does not work look at getting a rebuild kit for the carb. I wish that I could get hold of a online video for the carb WALBRO WT 170 as good as the piston and head video. However the manual I have got seems quite good.

By the way when I put the fuel in, the chain saw ran for about 5 seconds if that...but it was running very fast and that in my inexperienced opinion broke the ring. Maybe it was on the way out anyway??? I will look into getting a re-build kit for the carb.

Thanks again

rcmoser and other Techs, is it time to check the connector rod to crank bearings at this point? I retired an 80s Poulan S25 for parts since I own 3 (med grade saw). I was feeling/seeing too much wear in the stroke away from TDC (during a PM vs throwing a rod and trashing parts). I actually feel it was an accident to spot the wear since I was not looking for it vs spotting it.