Author Topic: Seals for cylinder head ports  (Read 1210 times)

Offline petertha

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Seals for cylinder head ports
« on: January 02, 2021, 09:25:23 PM »
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?


Offline petertha

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Re: Seals for cylinder head ports
« Reply #1 on: January 02, 2021, 09:28:36 PM »
Head port closeup. Sorry for the mess, deburring all the sharp edges with rubber abrasive

Offline petertha

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Re: Seals for cylinder head ports
« Reply #2 on: January 03, 2021, 01:23:52 AM »
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/

Online Jasonb

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Re: Seals for cylinder head ports
« Reply #3 on: January 03, 2021, 07:19:05 AM »
What about a thin copper washer, seals spark and glow plugs OK and won't soften when your head gets hot.

Online Roger B

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Re: Seals for cylinder head ports
« Reply #4 on: January 03, 2021, 08:21:14 AM »
If you can anneal the tubing (250°C in a domestic oven??) maybe you won't need gaskets at all  :headscratch:
Best regards

Roger

Offline petertha

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Re: Seals for cylinder head ports
« Reply #5 on: January 03, 2021, 05:18:36 PM »
Thanks for suggestions. I found a stick of teflon (apparently aka PTFE) on Ali for reasonable cost & shipping time. Its just not something very common around my neighborhood. I have a sense this might be one of those trial & error things, so at least I'll be able to make & adapt what is required. Fingers crossed.

Does anyone know what the red 'gasket' material is you typically see on RC engines in a washer like form? Its not rubbery like silicone. It almost seems a bit fibrous, but not super hard either.

While searching Ali I also stumbled on another obscure requirement - oddball OD/ID silicone tube to marry my induction pipe to the manifold (green shade area). Deviating from the plans a bit where the tube was supposed to continue & enter a permanent fitting in the manifold with an integrated O-ring. I had a tough enough time bending the tube right to get this far, so will cheat & just have an short, external flexible sleeve.

Offline petertha

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Re: Seals for cylinder head ports
« Reply #6 on: January 03, 2021, 05:29:23 PM »
What about a thin copper washer, seals spark and glow plugs OK and won't soften when your head gets hot.

That was my exact thinking too. Maybe I'm being a bit overprotective of these head port threads. They enter at the funky angle so have partial engagement for several turns. When fully engaged I have maybe only have 3 threads worth, so not a lot. So bottom line is I don't want to get too rammy with tightening like a glowplug if I can avoid. The design is metric but I'm making IMP. I actually increased the head diameter from original plans a bit for this reason. A bolt on face flange would be so much nicer, but it just didn't play well with the geometry & I didn't want to stray too far off the path. The larger head meant a larger cylinder top so was already becoming a rabbit hole.

Online Roger B

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Re: Seals for cylinder head ports
« Reply #7 on: January 03, 2021, 06:27:07 PM »
Best regards

Roger

Offline petertha

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Re: Seals for cylinder head ports
« Reply #8 on: January 03, 2021, 07:02:14 PM »
That sure looks like them visually. Not super high temp rating but then again I maybe I'm mixed up & they aren't used on the I/O ports. I'll investigate.

This range of red fibre sealing washers are designed to be use on cable gland entry threads.  They effectively maintain the ingress protection rating and are suitable for use in a temperature range of: -60°C to +100°C.  Browse our collection and choose from both Imperial and Metric sized washers.

 

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