Topic: Where did this come from? Nut in oil pan

[90blacknight]

Hello all,

I've got a 78 550k and upon removing the oil pan to inspect/clean, I found a nut sitting at the bottom of the pan. This has me concerned. It came from somewhere. The engine runs great with great compression across all cylinders. No mysterious noises or the like. Where did this nut likely come from? I'm I having to tear into this motor?

Thanks!

[Gordon]

Make a couple more posts and you should be able to add a picture, or tell us the size. 

My first thought is a valve adjuster nut.  Remove the valve adjuster covers and check to see if they're all there. 

[90blacknight]

Yes, same size as a valve adjuster nut except they are all in place. Perhaps somebody previously dropped a nut and then replaced it. Anywhere else this could have come from?

[69cb750]

This has me concerned. It came from somewhere.

I agree, it came from somewhere.

[HondaMan]

Yes, same size as a valve adjuster nut except they are all in place. Perhaps somebody previously dropped a nut and then replaced it. Anywhere else this could have come from?

The only other nuts inside the 550 that I can think of right now are the rod bolts' nuts. You'd sure know if one of those came loose! It it was a valve adjuster's nut, one side (at least) will have a flat surface that almost looks like a washer, where it is precision-ground flat to hold well. Many have this feature on both sides. Rod nuts are similar. They are fancier than ordinary nuts.

[PeWe]

No marks on the nut as it can get if enter the gearbox?

A std nut with no marks, no rod bolt nut means a happy ending

[Jerry Rxman Griffin aka MuthaF'er]

Do adjuster nuts and rod nuts have the same threads?

[bryanj]

Nope

[Don R]

Check the adjuster nuts to see if one appears different. If it does, someone lost one in the motor and replaced it. If the PO used a proper matching nut of course, that can't be proven.
  I lost a 1/4 X 3/4" bolt in a big block chevy that cost $3500 to repair. When we shut it off I heard it go tink in the windage tray. You may have gotten lucky. 

[90blacknight]

At first glance they all appeared to be the same, with the same blackened look, whereas this one is shiny; perhaps from sitting in the oil? I can verify the threads to see if this is indeed a valve adjustment nut. I'll post back later with some pictures.

[PeWe]

If same adjuster screw as CB750, fine thread not std nut.

[90blacknight]

Here is a the nut:

[HondaMan]

That sure looks like a tappet nut!

[Jerry Rxman Griffin aka MuthaF'er]

Coarse threads??

[flatlander]

yes, looks like a tappet nut.

[90blacknight]

So, given that the nut doesn't appear damaged, I should consider myself lucky and carry on? Thanks all!

[flatlander]

you may have gotten lucky.
of course, if you're the paranoid type, you'll ask yourself: what else may be in there?
but if the engine ran fine so far, it may have been sitting in that pan for decades already without anything else being wrong.

[90blacknight]

Yes running just fine prior to starting the mild restoration. Agreed, that nut may have been there for decades.

[754]

If its coarse thread its from the cam cap stud..