Mystery Nut in oil pan .... (!)

[jethro]

I removed my oil pan tonight. Laying in the bottom in the oil I found a small nut. (nothing else)
It looks to be maybe an M6 (measures .200 inches inside the nut)- it is a nut that has an attached cupped washer
(maybe an antivibration style) which swivels but doesn't come off. It appears to be nickel plated (?)
I looked up under the inside of the engine with a flashlight but I couldn't see anything that could have a nut that size.
I wondered if it could have been from under the rocker covers- but I don't see anything like that in there....
I didn't see anything that size in the front gear case when I did the KDP. Anyone have any ideas where I might look that it might have gotten into the pan from ?

The reason I removed the pan- on the bottom of the pan about 2 inches behind the drain plug there appears to be a small metal screw put in from the outside. The screw seems to be coming through and pushing up the doubler plate on the inside of the pan. It appears to be pushed up about 3/8 inch. My intent was to weld up the hole. What is the doubler plate doing ?
Is it supposed to be spot welded to the inside of the pan so it cant come up ? I think the engine sat outside resting on the pan- so I think the bottom of the pan got slightly distorted which might have broken a spot weld - and maybe why the screw is there. If that is so- I should be able to feel the residue of the spot weld on the underside of the doubler plate....... have to check that tomorrow. Do you think any of that makes me have to replace the pan ? OR do I just work the wrinkles out and weld the hole up ? ( the upper rim looks fine where it bolts on...)

Tim

[PToombs]

I would just tweak the pan back and weld it up. As for the mystery nut, no idea, I don't remember anything that small inside the engine.

[jethro]

Yes, it looks smaller than anything I would think is in the engine proper- It looks like an aircraft anti-vibration nut.
I thought while I have the pan off- I would check the torques on the mains and the rod bolts and whatever else I can reach.
it is very clean in there ...... basically spotless ! The cam surfaces look OK so far- no texture or grooves or chips. I have to rotate it around some to see the other faces.

Looking at the inside to the pan surfaces... It appears that the "liner" might be a thermal insulator maybe- it is a thin sheet metal liner that has stamped coin indentations which hold it off the pan about 1/16 inch- and it looks like it has spot welds done between the indented dimples and the pan metal. It looks like when the pan was pushed up on the bottom a little from the weight of the engine on it- it popped a few of the spot welds. not sure how the tiny hole got there- but I have to get access to the back of the hole to weld it- and that's under the thin sheet thing.
All I can figure is that the thin sheet is a thermal insulator to reduce the heat transfer of the hot oil in the pan to the cold air on the outside of the pan (in cold weather). That would explain why the created the dimples as standoffs to create a gap so that thermal conduction would be reduced. Maybe I can use the dremel to cut out a square or round hole in the thin sheet to get at the hole in the pan.......

Have to get to the back to clean the surface before welding....

So do yall think the loose bolt might not be anything that was from the engine ? (from its small size? )

Tim

PS- another web site thread mentioned this liner - that it was for lowering sound levels... I guess it could do that .....
It is made in two sections - one in the bottom of the sump and another on the rest. I removed the one in the sump.
The hole in the pan indeed was from the broken spot weld where that sheet was installed.
I think I wont put the one back that I removed....