how much extra oil in crank case will damage engine?
Make/model/year/how many quarts does it take as per owners manual?
Depends on the engine. We need to know what vehicle we’re talking about to give you a good answer.
Typically I wouldn’t go above a qt extra. Beyond that you risk the crankshaft whipping the oil into a froth.
Why do you ask?
it can vary depending on if the lower end of the engine starts a lot of foaming and the oil pump can’t pick up foam and deliver it as oil where and when it is needed. A small engine won’t have a lot of extra leeway and baffling is a factor.