I have my engine apart to replace the head gasket and timing cover gasket and I noticed today a small pin on the bench.  I'm not positive it is from the engine but I have never seen it before.  On the bench I have had the oil pump, head, timing cover, thermostat housing and the chain tensioner.  It doesn't appear to have an oily film on it but It could have been cleaned while I have been cleaning parts and scraping gaskets.  It has a black coating on it and has one small area that shows wear.  Any thoughts?

Is it metal or plastic? If plastic it looks like the push out center of the plastic interior panel rivets.

https://www.dkhardware.com/datsun-trim-panel-plastic-rivet-cp764361-product-14721.html

 

It looks like it is metal - a roll pin to be more specific. The bottom of the distributor shaft on a 240 would have one. The small gap along it provides a press fit - so not likely it fell out. I can't recall where another one would be located on the parts you have removed. You don't indicate the year or engine you car has but I believe the ZX distributor has a plastic collar at the bottom where the pin is located. Perhaps the plastic broke and the pin fell out. Just a guess, I'm afraid.

Both good possibilities.  Seems like both of those are longer than a dime's diameter though.  Not sure.  Need a better picture and a better description.   Metal, plastic, solid, rolled...

Its a 72 240Z.  Its solid metal and sticks to a magnet.  It appears to have a black oxide finish with some wear down to the base metal.  It isn't a roll pin or a plastic rivet.  Picture attached at a different angle. I saw nothing on any of the parts diagrams that this could be but like I said it just appeared on my workbench.  Thanks!

My vote is on the distributor but it could have just stuck to something and fell off when cleaned.

Your second picture indicates to me that it isn't a piece off of your Z. Perhaps the tool fairy had something to do with its appearance - hence the dime.

Its not the roll pin from the bottom of the distributor.  Thanks for everyone's input.  I'm feeling pretty confident its not from the motor.  I'll take my dime and leave!

Have you checked the ceiling?

I often stare at the ceiling as I lie awake and think of all the money I throw at the car!  

 

Me too! 

Then I put one foot on the floor and it stops. 

I was taught that if one foot on the floor didn't stop it, you should put two feet on the floor and get up. You aren't going to fall asleep anyway.