Bear with me here...
Last year I offered to adjust a friend's rod bearings in a 1929 Tudor he bought from the guy, who had "restored" it. Boy-howdy, was that engine noisy and rattly ("rattly"?). I was afraid a rod would come loose and go through the side of the engine block if the rod bearings weren't adjusted - and soon. Knock, knock, rattle, rattle. (Can you guess where I'm going with this?) While doing that, I also adjusted the main bearings, which is always a fun job when the engine is still in the chassis. I have adjusted rod bearings maybe 100 times in 50 years, so I kinda know what I'm doing.
Well, after making the adjustments and removing suspiciously few shims, I started up the engine. The rattling/knocking noise was still there! WTF??? I sleuthed around the engine while it was running and determined that most of the noise was coming from behind the valve cover. Off it came. Readers may register horror at seeing the photo of the pieced-together oil pump drive gear spring shown in this thread, but at least there IS a spring! Yup - "Mr. Restorer" had assembled the engine and NOT installed this all-important spring. You could lift and drop the drive housing to replicate the knocking noise as the engine ran. Installing a used spring I had on hand quieted everything down. This was the first time I had encountered such stupidity - and I thought I had seen it all. Jeez - didn't the previous owner wonder where the extra spring belonged after the car was assembled? Why are such morons attracted to our hobby???
I hope I am not the first Model A guy in the history of the universe to have been fooled by a loose oil pump drive gear housing because of a missing retaining spring??? For the life of me, the noise sounded like loose rod bearings. Honest! I could have SWORN that the rods were loose. As a matter of fact, when I finally discovered that this spring was missing, I DID do some swearing! A LOT of it.
Marshall