Gasket seal material for inlet port

[petertha]

I'm making up the induction tubes for my radial. 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 engage OK. Initially after trying different sizes & hardness of O-rings, I thought I found a good combination. But after closer inspection it still seems hit & miss. The ring wants to kind of flow inside the trumpet even with hard durometer. I noticed that a dummy flat washer I made from aluminum fits very consistently, so I'm thinking the issue is more about the section shape than the durometer. I tried looking online for something that might work, but I have odd ball size, about 11mm OD x 6-7mm ID x 1-2mm thick. I don't have a lot of wiggle room washer thickness wise. Its the induction side so max temp would be the head itself. But I also need something for the exhaust side. I was thinking copper for heat & the gas seal isn't an issue like the intake side so was less concerned about that right now.

Any recommendations or ideas?

I thought about buying a stick of teflon & machining my own washers to size. But would this be soft enough to deform a bit for gas seal with typical tightening pressure? I cant get too rammy on these threads as-is but mostly I didn't want air leak messing up the mixture.

 

[a41capt]

I'm making up the induction tubes for my radial. 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 engage OK. Initially after trying different sizes & hardness of O-rings, I thought I found a good combination. But after closer inspection it still seems hit & miss. The ring wants to kind of flow inside the trumpet even with hard durometer. I noticed that a dummy flat washer I made from aluminum fits very consistently, so I'm thinking the issue is more about the section shape than the durometer. I tried looking online for something that might work, but I have odd ball size, about 11mm OD x 6-7mm ID x 1-2mm thick. I don't have a lot of wiggle room washer thickness wise. Its the induction side so max temp would be the head itself. But I also need something for the exhaust side. I was thinking copper for heat & the gas seal isn't an issue like the intake side so was less concerned about that right now.

Any recommendations or ideas?

I thought about buying a stick of teflon & machining my own washers to size. But would this be soft enough to deform a bit for gas seal with typical tightening pressure? I cant get too rammy on these threads as-is but mostly I didn't want air leak messing up the mixture.

What do you think the max temp for that application might be? I’m printing TPU gaskets that seem to be holding up well on the intake side of my Weber engine, and perhaps I could gin up some of the appropriate size for you. The TPU I’m printing is supposed to have a shore rating of 95A, but I’ve printed thin parts (0.4mm) that are as soft as tissue paper.

However, 1 to 3 mm show compressibility, but not much deformation while sealing.

 

[petertha]

Hi. Subsequent to that post I ended up buying a stick of Teflon (or so they say it is) from AliExpress & machined some washers for both induction & exhaust just so they are the size interchangeable. The induction has to seal properly & see's average head temperature. I have ascertained it is sealing so the material has the right amount of deformation when the flange nut is tightened. Temperature wise (and I'm guessing a bit from RC experience) maybe 350-375F average head temp with air cooling?

On the exhaust side, I've seen flames out the exhaust stack occasionally & seem to recall a temp probe showing 450F on the header/pipe itself. But I also recall 4S (nitromethane) engines ran a bit hotter on the exhaust than 2S. I spent more time around 2S tuned exhaust systems & maybe sucking & reflecting some portion of induction charge cooled it a bit more than straight muffler type exhaust? Anyways, I haven't run my radial yet so can tell you how the Teflon worked out. Waiting on the Great Snow Melt (and I don't mean climate change LOL).

 

[Longboy]

You need to support the inner diameter of the O-ring with an equal or oversized dia. short brass tube so the flare compression doesn't collapse and punch in the O- ring up the port.

 

[petertha]

Thanks. I assume you are referring to my post #1 which was over 2 years ago now. As per post #3, if I wasn't clear, I abandoned O-rings altogether & now have a Teflon washer about 0.050" thick that mates the flange of the pipe flare to the head counterbore face.

 

[Longboy]

Thanks petertha. I see now the OP date. Yes, matching a flat or tapered seal to the flare tube for the intake via Teflon the right solution. Hope it supports the temps. My best guess is a copper seal for the exhaust side.