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Seals for cylinder head ports

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petertha:
I'm making up the induction tubes for my radial from 5/16" OD x .035wt aluminum versatube. The trumpet flaring profile is coming out reasonably consistent. They need a bit of dressing but in the end have ~ 0.030" flat on the end to match the internal port counterbore face. The nut seems to push against the tubing flare OK. Initially I thought I found a good size/thickness/durometer combination of O-ring. But after closer inspection it seems iffy. The ring wants to kind of flow inside the trumpet. But I noticed that a dummy flat washer I made from aluminum fits very consistently, so I'm thinking the issue is more about the rectangular section vs circular O-ring shape & durometer/hardness.

I tried looking online for something off the shelf that might work, but this is an odd ball size, about 11mm OD x 6-7mm ID x 1-2mm thick. I don't have a lot of wiggle room thickness wise. I thought about buying a stick of teflon & machining my own washers to size. But would that material be soft enough to sufficiently deform for gas seal with typical tightening pressure? I cant get too rammy tightening these nuts, the aluminum threads are kind of delicate & the weird entry angle. Mostly I don't want air leak messing up the inlet mixture. Max temp would be the head itself.

For the exhaust side I was thinking copper for higher heat. I'm less concerned with leak there but maybe teflon would serve the same purpose there?

Any recommendations or ideas?

petertha:
Head port closeup. Sorry for the mess, deburring all the sharp edges with rubber abrasive

petertha:
Maybe partially answering my own question. I made some washers out of UHMW & nylon today from scrap rods on hand. Both passed the air seal test. So if teflon hardness is about the same or maybe ideally a bit less, I should be good to go. Its rated at 327 deg C. Also didn't realize was the same as PTFE, so that widens the shopping scope. Have not ford a cheap supply for ~ 0.5" diameter stick.
https://www.nes-ips.com/teflon-vs-ptfe/

Jasonb:
What about a thin copper washer, seals spark and glow plugs OK and won't soften when your head gets hot.

Roger B:
If you can anneal the tubing (250°C in a domestic oven??) maybe you won't need gaskets at all  :headscratch:

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