What could cause a painless chancre type sore on penis, visible for over a month and not having had any sexual activities in the last 8months?

Chancre: The most common source of a painless chancre on the penis would be syphilis and suggest that you be tested for this as well as other STDs. This usually occurs within 21 days, plus or minus, of the exposure, and I cannot explain the long delay of 8 months. Suggest you see a dermatologist. For your interest, the word "chancre" comes from the french and means "little ulcer".