My 261 which is what the 026 evolved into came with a 20" bar. I have buried it in big oak and it handled it. Saves the back when limbing too. I prefer it with a 16" bar. I have my original 026 from 1992 but have only run a 16" bar on that. To answer your question i would say yes to the 18" bar.
Got the pieces I scrounged bucked to length and ready to split. That pile is 2-3 ft tall and close to 8 ft long. Should make close to 1/4 cord I think.
