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Serious knock in engine after oil pan change

Hi Ho, I am afraid I know the answer…I have a Ford Ranger 4wd, 2000 120k. Ran well, great shape, reliable and quiet running. Oil pan leaked and I got tired of going under and used Devcon in attempts to stop leak…reoccurring issue. So I dropped the $500 to get new 0il pan. Started it up following morning after driving errands and home from shop and saw a cloud of smoke on start up never seen before, cleared away and didn’t think about it again. Drive round trip for about 70 miles and while driving at slow speeds back in town, the oil gauge started pinging back and forth, and the knocking started. By the time I got home I do not dare to drive it anywhere as while the oil gauge does not fluctuate anymore the rapping has increased. What could have started this chain of events? Can I expect the garage to replace the engine? Vehicle is worth 4k replacing engine probably 3K…while a beautiful useful truck body sits in yard is it really worth it? Bad draw on the cards?

Often, when engines have significant oil leaks, the owners stop changing the oil thinking that the regular addition of a fresh quart is adequate.

On the other hand, some owners use the oil pressure gauge to indicate when a quart is needed.

Are either of those or similar scenarios relevant to the situation?

Yes. This:
"Oil pan leaked and I got tired of going under and used Devcon in attempts to stop leak…reoccurring issue. So I dropped the $500 to get new 0il pan. "

makes me think that there might be some more back story to the whole thing.

Who replaced the pan?
Did they check to ensure the pump pickup was properly positioned with the replacement pan?
Is it even the correct pan?
Was the pickup screen checked for debris?
Is the oil level correct?

The truck sat in a snow bank for a couple winters. surface rust weep leaks slowly formed on oil pan. Does not leak enough to add a quart in three months. Oil changed every 2-3k miles. Started with 76k miles and ran until about 125k with no serious oil leaks or low oil issues. Not significant oil leak, with todays inspections, the oil pan is wet they want to replace it. Devcon usually works for 6-7 months and then new weep or glue separates and old weep starts again. Never showed any evidence of smoke/burning, never checked oil to find needing any more than a small part of a quart. While it is a 4wd it is really used as a road car. No heavy loads or any off-roading. I have never seen the oil pressure gauge pinging back and for erratically until after this oil pan change was done. Bats right back and forth. It is expansive job because I believe the motor has to be jacked up off mounts to get clearance for oil pan. Could the oil pick-up been plugged with sludge? Could it have been started dry and caused the crank connection to seize? Could the pick up tube have been bent/misaligned on oil pan replacement? Local garage did work.

My wild guess is that the height of the oil pump pickup tube was not adjusted for the new pan and the knocking is the main bearings depleated of oil. The pump cannot draw sufficient oil to maintain pressure if the screen is against the bottom of the pan. There should be 1/4" to 3/8" clearance. You can calculate the clearance or check it with silly putty, but it needs to be checked.

If I’m right, you can get some consolation from knowing that you’re not the first to do this. A few years back I was watching a famous customizer show on TV and the pros made exactly the same mistake.