You'll be amazed at how much having a kid will realign your wants and perspectives. You'll give up stuff, but you wont realy mind, especialy when you figure out how to make the kid laugh so hard it sounds like he's choking on a duck.
It used to be rare to find me at home between the hours of 9 and 12pm on any night. Now I go a month or so at a time withough going out with the guys. Hell I'm too tired to stay up and enjoy adult swim most of the time.
A tip, Fatherhood starts at conception. When the lady is ripe with preggers, she needs you around as much as the baby will. Find a hobby that you can enjoy in the same room as her. I Draw, build models, etc etc
If you think about it, wrenching just gives you something to do. You need somethign to do, you liek doing that, so you do it. When you have a kid, that is something to do, and you will enjoy doing, so all will be well.