[Eric]

Alright, I've done a quick search and can't find anything immediately relevant, so I will ask a vague question.

Does anyone have any experience with a front-of-engine failure mode involving the balancer / front main seal / front pulley?

The story:
1997 318ti M44, 244,000mi, running well, 4 hours into a highway trip (75-80mph), engine temp normal, outside temps ~40°F, listening to the stereo, no sign of trouble, and THEN...
— "That tractor-trailer next to me is making a funny sound"
[Turns off Stereo]
— "Holy crap, that's this car!"
[Check rearview mirror to pull to side: Billows of smoke from the back of the car]
[Noise gets louder, tiny guy with jackhammer inside of engine]
[Signal, ease off of gas, pull to side, take exit ramp that is right there, coast to stop, engine felt no decrease in power, and still running fine, billows of oil-smoke from under hood now, and coming in the A/C vents]
[Turn off engine, raise hood]
Under hood, it was obvious that about a quart of oil had come out through the front main seal, oil pan is fine, no other visible damage.
Engine restarted easily, idled normally, jackhammer sound was LOUD, flashlight check showed balancer wobbling slightly, serpentine belt is now 1-row off of the balancer pulley.
Never lost oil pressure at any time.

$200 and one day later, the car is back in my driveway, thanks to AAA, and I need to start disassembly as soon as I have some time (looks like the 330ci will get some autumn use this year). Review of parts photos and exploded views makes it apparent that the crank and block may still be intact, and damage could be limited to the front timing case cover and, presumably, the balancer. The jackhammer sound has a bit of a timing chain quality to it, but I can't see how the engine would run if the chain were that loose, so I have to imagine that the chain is still tight.

Has anybody had or seen a similar problem?
Should I be looking for a timing cover and balancer, and some chain guides, or should I ASSume that the front main bearing has damage and start scheming the removal of the (good-running) engine from my parts ti?

Any background on this would be appreciated, so I can plan out the repair, as I won't have a chance to crawl under it and pull the balancer and cover for at least a week, if not two.

Thanks,

- Eric