teflon as a crankcase gasket material?

[petertha]

I've been testing different methods & materials for what will ultimately be my radial engine crankcase sealing decision. I'm not super happy with my test result implications thus far, so was wondering if anyone has experience using Teflon?

The pink line shows a path where oil could migrate externally between 2 mating parts. On the left side is the engine nose chamber which is partially filled with oil for bathing the gears & cam lobes. The designer calls for O-rings as seals between various components, 1mm section diameter. I'm finding that achieving the correct groove depth & nominal O ring diameter (made from cord line stock) is a bit fussy. Too shallow & the parts bind up. Too loose & I doesn't seal.

I think I can handle the radial O-rings ok, but the one on the CC face right by the pink line has me more concerned. I'll only have one shot to make that groove correctly & there will be a lot of machining operations on the CC before knowing for sure. Its also very close to the edge which I don't like.

My first idea was to cheat & bypass the CC face O-ring altogether. I bought Permatex RTV gasket caulking & tried on a test piece. It sealed perfect but unexpectedly stuck my test parts together like glue. Maybe FS auto parts have leverage to crack the seal but I'm concerned about my fickle little model components - there is nothing to grab onto for leverage. I tried some release agent which helps but this seems like a PITA if I have to re-assemble engine many times. I tried another silicone which was weaker but I don't think its intended for oil service like this.

Looks like the thinnest Teflon sheet comes in 0.002" thickness @ inexpensive 3$ for 12x12". Being that thin, it wont require altering dimensions of mating parts to compensate thickness. But I'm wondering if the Teflon itself might be 'hard' relative to softer gasket materials, ie. will it seal? The thinnest conventional (softer?) gasket sheet I can find is 1/64" (0.016"). Silicone sheet comes in 0.005" but its 31$ for 6x8".

Any thoughts or experience?

 

[mayhugh1]

Peter,
I don't have any experience with thin teflon sheet as gasket material, but I have used oiled high linen content stationery. Around here it is sometimes referred to as 'rag' paper. I've been pulling sheets out of a 30 year old university dissertation as it was required for such works because it lasts practically forever. It is about .004" thick and easy to cut with an X-acto knife. I've also cut up new US one dollar bills for small gaskets. I coat them with oil also. Our dollar is also a high linen content paper with other 'secret' ingredients.
If your machined surfaces are clean and flat you don't need much for unpressurized oil seals. - Terry

 

[Jasonb]

I usually use a liquid gasket which sounds much like your RTV one, if you are having a job getting the parts separated again then add a couple of tapped holes around the flange that can be used to take jacking screws. You quite often see these on the cylinder covers of old engines. If it were a hardet material a couple of slots for a lever could be added but being aluminium it will bruise.

Bogs has shown thin Mylar sheet being used for gaskets which would be an option

 

[grapegro]

I find that aviation grade Permatex is a good gasket for mating surfaces, it does not set, does not leak and can always be undone. It is by name, used exstensively in the aero business.
Norm

 

[GailInNM]

Teflon (PTFE) works very well for gaskets. It is doft enough that it flows into the micro grooves from machining to form a tight seal. Although Mylar, as Bogs uses, will work the finish between the parts has to be better as it does not flow as PTFE does and a higher clamping pressure is necessary.

Steve Hucks used PTFE on his Little Demon V8. He used 0.,010 for all the gaskets except the head gasket which used 0.020. I use 0.008 thick for the head gaskets on all my small engines and 0.005 for other sealing gaskets.

I would hesitate to use less than 0.004, or maybe 0.003 for sealing gaskets if //the part finish is good, I think it woudl be too thin to flow to make a good seal or would require more pressure to make a good seal.

Vegetable fiber gasket material is also available down to 0.007 but hard to find in small quanities. It is not as tough as PTFE but works well.

Look for a PM.
Gail in NM

 

[kvom]

I have used teflon sheet as gaskets for my last two engines. I'm sealing air, not oil though.

 

[toolznthings]

I find that aviation grade Permatex is a good gasket for mating surfaces, it does not set, does not leak and can always be undone. It is by name, used exstensively in the aero business.
Norm

I agree on this recommendation. Works very well and requires very little to make a seal. Have used it for years on my LeBlond lathes head stock cover which has a full oil bath on the internals. No leaks.

Brian

 

[platypus20]

I use .020" Teflon gaskets to seal up high pressure steam boilers, running at 230 psi, with no issues.

 

[petertha]

Thanks for all the suggestions guys. I now have some new tricks to try & will report back my findings.

Interesting suggestion on the US$ bill Terry. I forgot about the linen content. I was going to joke that a US$ bill gasket was going to cost me 1.315$C. But it gets worse. With loonies & toonies our bills start at 5$ & they are now high tech plastic. Who knows, maybe Teflon! :thumbup:
https://en.wikipedia.org/wiki/Banknotes_of_the_Canadian_dollar
https://en.wikipedia.org/wiki/Polymer_banknote

 

[Hopper]

Another sealant to try might be Hylomar. It comes in a spray can so you can put a very thin layer on. You let it go dry then bolt the parts together so it makes a sort of formed in place thin gasket. Does not stick as hard as silicone.

 

[petertha]

Thanks Hopper. I have not heard of that brand before. I notice they also make a goop form & the user comment was 'comes apart easy'.

I was translating the engine build instructions & just noticed he also makes reference to sealing the bolts too, so I might need some form of goop anyway. I'm less concerned fasteners because they have something to wrench on & break the seal. But as mentioned, I was quite amazed at the adhesive power of RTV on clean & shiny mating aluminum parts.

https://www.amazon.ca/dp/B003TQ07P0/?tag=skimlinks_replacement-20

 

[gmac]

Peter;

Try ThreeBond 1194 (Japan mftr) - the motorcycle industry has used it to seal cases and covers for ages - non-hardening.

http://www.gwcycleworld.com/threebond-threebond-liquid-gasket-grey-detail.htm?productid=10275615

..... if you're a Yamaha fan ask for YamaBond - basically the same stuff.

Cheers Garry