Broken Circlip on oil pan drain magnet

[patrickt]

I have seen engines get pulled and disassembled for pieces of "stuff" found in the oil pan that were never traced back to a broken piece of something in the engine itself. OTOH, there are a lot engines out there still running strong where the owner found something in the oil pan and decided "well WTF it's been in there this long, what harm can it do?" If your Blackstone report comes back with an abundance of wear particles then it's hard not to pull the engine and take it apart. But if your oil comes back fine and you can't come up with a clever way to inspect all the interior circlips without pulling the engine and taking it apart then you're faced with a tough decision.

[Gaz64]

Looks like a wrist pin circlip. An internal circlip. Rocker shafts are likely to be outside circlips.
Wrist pin circlips can dislodged and fall easily into the oil pan, more easily on a non-full skirt piston.
I would pull all the spark plugs and borescope all cylinders with each cylinder at BDC.
A wrist pin walking out will start to mark up the bore. A compression test of the whole engine may reveal a difference large enough to inspect a low cylinder first.

[patrickt]

Uhhh, couldn't you just run the engine really hard and see which bore seizes up first?

[Steve1979]

To add on to what Gary said. This happened to me a long time ago when I built a Z code 390, bored 0.080 over with a borrowed 406 tri-power setup for the top. The engine was going into a 1957 Ford short tail. During the build, when I was getting ready to put the pistons together, some friends came by with some beer to help (what could go wrong). The pistons were assembled, put into the block and the rest of the assembly seemed to go well, It ran really strong for about a month and a half, until I developed what seemed to be a miss. During a compression test, coolant came shooting out of one of the spark plug holes. After pulling the head on the problem side, I found a big gash in the cylinder wall. On disassembly, the problem was the wrist pin was hitting and eventually broke through the cylinder wall. I couldn’t find the internal snap ring or pieces of it anywhere. So either it was left out during the build, put in backwards or not installed all the way into the groove. When I read and saw your picture, it brought back some memories.
Hopefully you caught this in time before there is any visible damage. But you may have to pull this engine apart to be sure where that piece came from.
Best,