Teflon vs. Viton seals

[Topcat]

I was going to put Viton seals on my list for the re build parts to buy. But then I saw these.

http://cgi.ebay.com/ebaymotors/MOPAR-FORD-VALVE-STEM-SEALS-TEFLON-POSITIVE-STOP-3-8_W0QQitemZ310106335332QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item310106335332&_trksid=p4506.c0.m245&_trkparms=65%3A1%7C39%3A1%7C240%3A1318

Any particular brand name or type recommended for a Hemi? Are the Teflon better?
Also specs/size if possible I should get.

Thanks

[71chally416]

The trouble with teflon seals is they choke ALL the oil off the valve stem. You need a little lubrication in a street car. Unless you have to have a small seal because of your inner valve springs I'd use a rubber Viton seal that lets a little oil into the guides. 

[AMXguy]

Maybe my teflon seals were bad or something but after 2 years of fighting oil burning on my rebuilt 440 I pulled it this winter, we decided the teflon seals were bypassing too much oil so we replaced them with viton. I fired it today for the first time and no smoke at all. I know I must have had some bad luck or something but I'm done with teflon, I'm so sick of fighting this I could scream.

[Chryco Psycho]

we use the steel body seals with the rubber lining

[The Cuda Guy]

So what is the correct answer for his application?

Don

[71chally416]

we use the steel body seals with the rubber lining

Me also too. 

[Changin Gears]

we use the steel body seals with the rubber lining

Thats what I use.

[moper]

There are issues with teflon seals taking the shape of the guide when new, but after some miles on street cars, the sealing surface of the valve seal (the part that rides on the stem) still is fine. But the area that seals on the guide becomes stiff and does not seal well all the way around the guide... So it sucks oil up under the body and the sealing surface has no chance to work. I havent had that. But I've seen it happen. There is no such thing as stopping 100% of oil. with proper guide clearance, you will not sieze a giude. But proper means tight when you're talking teflon. If the valve can move around too much, as I said, the seal can't flex very well to keep sealing. If you're not installing bronze guides or liners, tefflon won't seal for long. Because the clearances with iron guides allows for too much movement for the positive seals to work with long term.
In my opinion, the viton seals are the best bet, but teflon will work fine if the machine work and parts are good.   

[AMXguy]

You might be onto something there. my clearances were up to .002 with steel guides which is well within specs and my teflon seals leaked from day one, when we pulled the headers off the brand new engine at the dyno I could see oil on the exhaust valve stem. the viton seals are doing the job, but they're much softer and flexible than teflon.


 The 906 heads for my next project have silicone seals and bronze guides, but they say silicone isn't very heat resistant so I think I'm going to change them to viton.

[moper]

My bronze guides or liners get .001-.0015" clearance and the guides are honed, not reamed. .002 isnt bad for oil control when the rubber umbrelas are used. But when it's a hard seal like Teflon... they can also crack in use if the valves move around too much. Reaming guides leaves a lot of slop because the hole ends up being tapered like the reamer. You get a lot of seat runout that way too.

[71chally416]

Any machine tool is only as good as the machinist using it. You can have the best equipment money can buy and still screw up a valve job.
I'll bet the majority of automotive machine shops can't even show you their valve seat runout gages because they don't have any.

[AMXguy]

True, the book shows up to .3725 but that would have been with stock umbrellas.  so I guess if you're going with a positive seal and you're not positive you're close to .0015 you better stick to something soft like viton , silicone  or maybe even stay with the umbrella.

 On the subject of teflon seals though I noticed they're not all the same, mine that leaked were a white one that felt more like soft plastic, but the machine shop had some Hastings ones that were much more like rubber, so brand might make as much difference as material type.

[moper]

Any machine tool is only as good as the machinist using it. You can have the best equipment money can buy and still screw up a valve job.
I'll bet the majority of automotive machine shops can't even show you their valve seat runout gages because they don't have any.

Amen Brother!!!!!!

the three biggest BS claims "Yeah, we sonic check everything" (and dont own a tester)
                                     " [insert head manufacturer name here] seats are fine right out of the box" (and dont own the runout gage)
                                     "Of course we will plate hone your mopar" (and they dont own the plate)
All of these happen daily around my area...lol.

[71chally416]

A local machinist (now retired) told me a story about a big engine rebuilder that came to his shop to see his valve grinding equipment. He showed him how he put the mandrel in each guide to pilot the seat cutter and the guy said "We can't take that much time to do this so we don't use mandrels".