The original engine in my 94 pickup 22RE sounded very much like a diesel. I was sure it was the timing chain but it actually turned out to be a spun bearing. The original owner didn't believe in routine maintenance and when they finally did change the timing chain they did not bother to clean any of the debris out of the oil pan. Therefore the oil pickup was blocked and starved the bottom end of oil.

4crawler.com has a really good tutorial of changing the timing chain without removing the head if you find that is the problem. I'll be using it later this year (when it gets warmer) to do the T chain on my 88 runner.

Good Luck!! Jim