oil change, spring on oil plug Options

[vintage914racer]

So I decided to change the oil on my racecar myself, after usually having my mechanic do it during check ups, and was surprised with a spring behind the oil plug. At first I thought nothing of it, until I let all the oil out and tried to put the plug back in. To make a long story short it took a lot of time, cursing and effort to get the thing back in. What I am wondering if is this something on all 6 cylinders, or is it something special? I've changed oil in plenty of other cars, but have never seen anything like it. I remember my mechanic talking about some kind of oil pressure thingy down there, but right now my memory fails me.

[vintage914racer]

If anyone cars, I figured out the solution to my stupidity. I have an early engine with no drain plug. In order to drain my oil I just loosen the sump plate and the oil drains out. I did in fact erroneously remove the oil pressure relief valve from the plug which I thought was the drain plug. My mechanic says changing the oil the proper way will remedy my problem. Thanks for the help.