Hi everyone, long time lurker, and most questions I can get answers from everyone here with a Google search, but I'm a little stumped on this one. I have an i6 200 in a 67 mustang, I had it rebuilt in January by a reputable machine shop, and I'm finally close to installing it. I wanted to paint the block this weekend, so in preparing, I flipped it upside down to get the oil pan off.

I heard a dink dink dink, like something tiny falling inside the motor....the sound did not repeat when rotating again. So I prepped and painted.

After letting the paint cure today, I used a endoscope to look in the log manifold and firing chambers, could not see anything loose that would rattle around. Flipped it upside down again.

The distributor oil pump drive shaft fell out. I looked all over the crank case with a high power flash light and I can't find a loose clip or anything. Everything looks properly assembled.

So...two questions:

1. What could have possibly made that sound? If something is in the log manifold, what's the worst damage? Trashed valve? Or if the clip is in the crankcase somewhere, will it deflect off whatever its stuck to and sit in the pan once the engine starts?

2. Is replacing the oil pump at this point as simple as i think it is? I'm going to check the paperwork and if its the original one it looks as simple as four bolts, i could swap it and get an arp drive shaft.

Now that I'm finally asking questions, I'll have to get my intro post and some pics of the project up stat. Thanks everyone.