What am I looking at - spark plug hole #1
 

I have been inspecting my cylinders and pistons with a borescope, but when I tried to do #1 (right side front) I saw this.
http://986forum.com/forums/uploads02...1552935952.jpg
Looks like a washer, the hole in the middle is big enough for the plugs electrode to pass. Is this normal?

The rest of the holes look like this, which is what I would expect.
http://986forum.com/forums/uploads02...1552936069.jpg

Left-Over Washer
 

Maybe a washer left over from a home-made spark plug tube removal tool?

The engine was running fine when I removed the spark plug, whatever it is it is solidly held in place.

If you gently feel around with a brochette skewer or something , can you feel the piece?

Looks to me to be an "oil fouled spark plug saver" type of device. The intent was to have a central port (the hole you see) for the spark plug to fire through, but prevent oil scraped from the cylinder walls from reaching the plug.

Yes I did that, I used a metal rod to more than gently explore the surface and the hole... it is solid.

That sounds like an explanation... I was thinking something like that, but more in terms of controlling the spark. If it is what you suggest is this common on Boxsters or Porsches and why only 1 cylinder?

No, they screw in from the outside just like a spark plug. You'd see the hex shaped area where the wrench fits to it just like a spark plug. What he's got there is bizarre looking. It almost looks like a previous plug broke when taking it out and some piece of it was left in there? Damn, I've never seen anything like that.

That is totally bizarre. So that is at the bottom of the threads for the spark plug!? In other words at the top of the cylinder? And the plug you pulled was properly seated and engine running well? That makes no sense. What could that be? And no, it’s not “normal” for a Porsche engine.

Valve spring retainer?
How...?

So odd.
Compression tester that broke off?
Can you measure the depth of the threads and compare to another hole, so we can get an idea how deep it is? I mean, is it bottomed out in the threads? If not, could we assume it's threaded? If so, Google "internal pipe wrench" or "nipple extractor".

Dunno. Weird.

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does a direct light either around the edges or through the center reveal anything? does this move side to side at all? can the borescope fit through the center>

Is it somehow a reflection of the borroacope itself? Odd explanation....but very odd problem.

that's what i was thinking, as you will encounter some of the pistons at TDC.

did you crank the engine and check it again? Could be the piston top?

Well, I'm glad to know that it is not something obvious. Hare are a couple more pictures.

http://986forum.com/forums/uploads02...1553027715.jpg

http://986forum.com/forums/uploads02...1553027765.jpg


Yes it is below the bottom of the threads and yes the plug was properly seated, looks the same as the 5 other plugs in terms of colour and there is no indication that the electrode was touching the "washer", so the "washer" must be well below the bottom of the threads. The hole is too small for the electrode to protrude through it. Yes then engine ran fine, although I only put about 200 miles on it between buying it and putting it away for the winter.

In the above pictures you can see the piston crown through the hole, the pictures in my first post were with the piston at or near the bottom of the stroke... I turned the engine so it is at the top. No the "washer" does not move, the silver ring around the outside edge of the "washer" looks to me like it could be solder or welding.

I think the fact that piston crown is visible eliminates the possibility of it being reflections. I have other pictures, plus what I saw as I moved the borescope around, that leave me certain that that is the piston we are seeing through the hole.

So, one far out explanation that came to my wildly imaginative mind was that someone was strengthening the head... perhaps a crack around the spark plug hole. That seems ridiculous even to me to do that inside the cylinder.
One other interesting fact, when I did the compression test this cylinder was slightly higher (5%) than the others. I imagine having hardware taking up space in the combustion chamber would contribute to that.
It would be very interesting to drop the engine and remove that head... but if it continues to run well I'm not going to do that.
Anyway, the plan is to get it back together and start it. If it still runs like before it will go back on the road. I may keep my eyes open for a good used engine just in case...

EDIT - I just saw Gilles' question... I did pass a steel rod through the hole and it went a couple of inches before hitting the piston, this was when the piston was at the bottom of the stroke.

Could be that that the previous owner installed a 'spark plug extension'..? those things where used to keep the spark plug from getting fouled with excess oil (when a particular cylinder was burning an exesive amount of oil), perhaps one of the old gear heads here remembers them..

If I remember correctly, you were supposed to thread them on the spark plug threads, then you bolt the spark plug on top of it .

EDIT: If you install a plug back on this cylinder and measure the distance (depth) from the tip of the plug to the valve cover, and then do it again with another cylinder you can see if the plug on this particular cylinder sticks out further than the other plugs, then you have an extension..

Not to state the obvious, but I have looked down more spark plug holes than I'd care to think about, and whatever that is, it is not correct and does not belong there. The next question is what do you intend to do about it?

I note that the threads in #1 look much cleaner than the threads in the other hole without the "gizmo", so if we take the theory that it is to stop oil, it appears to have worked...
Never saw anything like it, and now I want to know what it is...

I figured it out!!! It’s a flux capacitor! Cool!

Looks like a conical trim washer to me. :confused: Other than that, nothing to contribute.