im getting a +12 for my f4 but the thing is since im getting a new chain do i need to change the front sprocket too, will the old front sprocket damage the new rear sprocket and the chain?

 

I would get a new one. That way they all wear in together
You cuold prolly get away with using the old one but it will give you more problems down the road

 

front sprokets are pretty cheap anyway, talk to a few people running f4's and see what they run for gearing. my friend just went down 2 in the front up 10 in the rear it goes pretty good but he wishes he went up 12 in the back.