I Messed Up!

The oil pressure gauge on my 230 diesel has been acting up for awhile now dropping down and coming back up and I've been meaning to change it. Well I found out last week it wasn't messing up. It dropped to 0 and started knocking. I drove it back to the barn and the pressure would come back up and it would stop knocking. Yesterday I put my pressure checker on it and fired it up and 60 lbs of pressure and no knock. Well I let it run for a minute and it fell to 0 and started knocking so I shut her down. The reason I thought the gauge was bad is this engine was rebuilt by a reputable shop here in Memphis about 15 years ago and it sat on the pallet with all of the rest of the tractor until about 2 or 3 years ago when I bought it and put it all back together so I assumed it had a new oil pump in it and that's why I though it was the gauge. What do you guys thing I messed up? could it be possible that all I will have to do is put in a pump? I've never been into a MF before so I need your advice as to what and how to check things. And I was so glad I finally had the 2 stage clutch adjusted so it would work. Thanks for all of you experience and help with this new problem.

well if you can hear the knocking, then you have already engine damage. time to check brgs. also.

If you heard knocking its to late. I would definitely go thru the bottom end before i ran it again.

FIL was less than 3 years old and did the same thing,i dropped the pan and found the oil pump relief spring had broken,replaced it and it hasn't given any more trouble,hopefully you haven't damaged yours.