Is it bad if i have a erection lasting more thn 4 hrs?

Yes: A continuous erection lasting more than four hours not only is painful but causes ischemia parentheses (low blood flow) to the penis resulting in potentially permanent damage to the erectile chambers.

Yes : When an erection lasts more than 4 hours (aka priapism), there is stagnation of blood in the penis leading to oxygen depletion to the cells leading to cell injury and death and subsequent tissue damage, scar formation, and impairment in the ability to obtain or maintain an adequate erection (erectile dysfunction). This is a medical emergency requiring prompt intervention.