The blob from the black CHT lagoon

I'm fitting 4*CHT thermocouples to monitor the new motor in my PA-12. Cylinders #1 and #3 installed just fine, but the probe fitting wouldn't catch in #2 and the whole hole felt too short and too wide, the same probe went into #4 just fine. I tried again with #2 using the probe from #4 and it still wouldn't fit, which obviously pointed to the cylinder and its CHT mounting hole.

I removed the oil tube and intake pipe from #2 and managed to get this photo of the CHT mounting hole



there's obviously something shiny and blobby lurking in the CHT hole!!!! My theory is some molten weld or similar has dropped into the hole at some point whilst the cylinder was lying on a bench or floor, or something was in the hole when the cylinder went through some kind of heat cycle?!!

Measuring past the blob, the hole depth is 1.250 and the thread is correct at 3/8 32. Lycoming have suggested drilling out the blob to probe diameter, but being v.careful to not deepen the hole, so the CHT probe can snug up against the face at the end of the hole and get a proper reading and we're doing this tomorrow, so all will be fine, it's just a mystery of what it is and how it got there!!!

Has anyone ever seen something similar before!!! :roll:

Looks like metal from fabrication or repairs. Use a thin punch and smack it a couple of times. That is usually enough to dislodge it.

Web

wireweinie said:

Looks like metal from fabrication or repairs. Use a thin punch and smack it a couple of times. That is usually enough to dislodge it.

Web

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sounds like you’ve come across THE BLOB before Web?!!

Plenty of times, although this is the first time I've seen this in a CHT well.

Web

wireweinie said:

Plenty of times, although this is the first time I've seen this in a CHT well.

Web

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This one was clinging on tightly Web :roll: so we used a smooth tube with a drilling bit on the very end to get rid of it!!

Ibefore



and after!!