If melting of the polymer is your main worry, try to find some nylon or possibly PET film instead ? But I guess gradual thermal degradation will probably happen to anything organic. I doubt that cling-film (polyvinylidene chloride, not quite PVC) will last long.

I picked the compressed aluminium foil out apart from an annular ring that I couldn't shift, which had probably been infiltrated with epoxy, which I just tapped through.

I coated the tap with candle wax in an attempt to protect the intact threads. I used a spray grease in the hole, which probably wasn't thick enough for the job, and also meant I could see the tap removing aluminium from the intact threads, which I didn't enjoy, so after a while I gooped it all up with a heavier (I assume molybdenum)grease salvaged from a scrap CV boot.

AFAIK you can't easily get international brands of grease in Taiwan. This is probably because grease (unlike oil) is mostly a pro product, and the pros don't care.

Got quite hard to move when it hit the epoxy, but I elected not to remove it and clean the flutes because I was concerned about further damage to the intact threads. This was probably a mistake.

Plug now runs all the way in, so assuming it doesn't blow out when/if the engine runs, I guess its fixed

HUZZAH!

If I was doing this again (hope not) I might use epoxy-reinforced compressed aluminium as the "filler", though I don't know if any epoxy was retained in the threads and it may be the tap alone did the job.

I would have preferred to try a forming tap first, but that turned out to be another case of Taiwan Unobtanium.

Now I just have to put it back together and hope that cylinder liner doesn’t perforate.

Edited by edlithgow on 25/05/2023 at 00:55

Wonder how much gold leaf is, (for that hidden bling thing.)

It's remarkably cheap, but it's also much thinner than aluminium.

Wonder how much gold leaf is, (for that hidden bling thing.)

It's remarkably cheap, but it's also much thinner than aluminium.

Use more layers. Good lubricant (I'd guess) and electrical conductor.

Unsure about load bearing though..

Gold leaf is about 0.5 microns thick, human hair is 60 microns.

Offhand, the only practical engineering application I can think of is coating for artificial satellites / space suit visors, for reflection of sunlight.