Any history on the car? Maybe left behind from other owner?

 

Check the oil pick-up tube. There are two 10mm nuts at the pick-up tube and one at the brace. I am not sure if the oil passages are big enough in the head and the block to pass a 10mm nut through but it definitely looks like it got thrown around by the rods and crank at some point. The good news is that it did not come down through a cylinder or the car would not be running good (if at all).

 

I agree with Rampage. Check the oil pickup. That's about the only place inside the engine that uses a 6point hex nut.

 

Well, I'm feeling a little better about the 'find'. The oil pickup tube or brace as the origin of the nut makes sense. I know that the pickup tube nuts are firmly in place but I can not recall actually putting my eye on the brace nut. It seemed plenty sturdy though.
Never having seen a photo of the inside of a Spyder's oil pan I was impressed by the size of the baffle, (aligning the pickup tube with the relatively small triangular opening in the baffle when putting it back on was kind of a trick!). The nut was found on the bottom under the baffle when I was cleaning out a thin layer of sticky sludge from the bottom. It must have been stuck down because I didn't hear it rattle around until I started wiping out the bottom of the pan.
From the look of the nut I assume it must have bounced around above the baffle for a while to be scarred and crushed the way it was. However, when the pan was off I inspected the bottom end with a flashlight and I didn't see any indication of scratches or marks on the crank, or rods.
I don't know much about the history of the car except it had some repairs on the rear bumper area. I'm pretty sure the oil pan had been removed at least once before I bought the car from the looks of the "gasket in a tube" stuff I had to clean off.
Thanks all for the timely responses!

 

I'm late to this party, so all I can say is WTF!!!

 

If it was fine with the nut in the pan, i'm sure your engine is fine with it out!! :lol::lol:

 

I'd be more concerned finding a crushed nut in my briefs.

 

++1 Dang you beat me to it. Maybe the title should say "I found my nuts crushed in my oily pants".
Sorry cant help it!

 

My pants might be a bit oily but MY nuts are fine. However, the suspected origin of the errant hex nut isn't the oil pick-up tube or it's brace. Now I'm back to freaking out a little!


You can see the brace is held by a bolt, (yellow circle), and the tube hex nuts, (arrow), are different than the nut I found in the oil pan. I know, I know. You can't see both of them but the other one is there. I was trying to take a pic of the piston chamber from underneath. And that weird thing in the oil pick-up is a paper towel saturated in oil.

So I'm back to asking for ideas of where this little sucker might have come from.

 

Maybe it was there from the factory?
If surgeons leave swabs and tools in patients, maybe a stray bolt made its way into the assembly line

 

All the 10mm nuts used on the engine seem to be flanged. The one you found does not appear to be so it is most likely foreign to your engine. I have looked at the blow-up of the engine and the only internal 10mm nuts I see are the oil pick-up nuts. Maybe the PO (or his mechanic) dropped it in the oil pan it they had it off. It could have also been dropped in during a timing chain replacement or possibly when installing a new timing chain tensioner. If the engine is running good then it apparently did not do any damage. I do not think it was holding anything in your engine together.

It might even have been in there since the oil pan was manufactured.