Small Engines (Lawn Mowers, etc.): craftsman tractor/B&S engine, engine model type, engine numbers

Question
I heard a pretty loud pop the last time I used my craftsman tractor, just before I turned it off.  I was done, so I figured I'd deal with a problem the next time I used it, if there actually was one.  Yep there's a problem...

It starts fine, but there was another loud pop.  I turned it off and checked the oil.  I was shocked to find that there was virtually no oil in it.  A shock because it was fine the last time I checked it a few weeks ago, and there was no sign of leakage.

I filled it with oil, and started again.  Pop!  But it was running, but with less power than usual.  A couple of more pops (snaps?) and I let it run just a bit more (2 or 3 minutes), as there weren't any more alarming sounds.  I drove it about 15 feet until I saw oil leaking.  I stopped the engine immediately and found the oil leaking out of the side of the engine.

I can't find anything on the web that will help me diagnose the problem, but I did find this site...

Any suggestions?

Answer
What is the engine model, type and code number?  I need to look up your engine.  If you have a l-head opposed twin cylinder there is a plate on the back of the engine you can remove to inspect the internal parts.  You will have to remove a few bolts (4-8) to remove the inspection plate.

Send me the engine numbers so I can look up the parts diagram.

Eric