Spun Main Bearing?
 

So I have a 96 4.0L Ranger. I let my father use it for about a month while I was at school and now there is a loud knocking sound under the hood and I don't think it's even driveable. I haven't tried nor have I put a stethoscope up to it, which from reading other forums, is what I should do? However, what I'm trying to determine is whether or not my dad's prognosis could be viable. He believes that it is a spun main bearing. SO my question is, what does a spun main bearing sound like? And what does a busted rod sound like? This sound is pretty freaking loud, and there's chemical/burning smell upon disengage.

Thanks

The answer almost seems irrelevant. The engine needs to be pulled in either case to correct it.

Forget the stethoscope and drop the pan.

If the rod or main bearing spins the engine will lock up. If the engine is still running the bearing is going out and the crank is probably bad now.

Your going to have to pull the engine to replace the crank but I would still pull the pan and have a look.

On the other hand it's toast so pull it.