Thanks to a post by Kirbert I now have a source of Teflon stem
seals. However I see that some people are talking about using
Viton which supposedly lets some oil down the stem. These are also
available through the same supplier, silver-seal
Is there any more information out there regarding the best
option.–
Mark Brown 71 S3 Etype
Ohope, New Zealand
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In reply to a message from 42southern sent Sun 31 Oct 2010:
IMO, I favor a stem seal that allows some oil down guide, its
better than wearin out stems or guides. some yrs back teflon
was all the rage, but like anything improvements come along.
that said, the type seals that have a good flexable contact
and havw a small circumference spring, IMO are best today!–
The original message included these comments:
seals. However I see that some people are talking about using
Viton which supposedly lets some oil down the stem. These are also
available through the same supplier, silver-seal
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
3
42southern wrote:
Thanks to a post by Kirbert I now have a source of Teflon stem
seals. However I see that some people are talking about using
Viton which supposedly lets some oil down the stem. These are also
available through the same supplier, silver-seal Is there any more
information out there regarding the best option.
I can report that I drove my '83 for thousands of miles after
installing those Teflon stem seals and had no problem with them.
Didn’t burn oil at all, ever. If I were doing the job again, I’d go
with the Teflon stem seals again.
I did apply some graphite to the valve stems during installation,
dunno if that did anything. My figuring was, if no oil ever came
down the stem, maybe the graphite would stay put, and if oil did come
down the stem the graphite wouldn’t be needed.
One thing is definite, though: You won’t be using any high-lift cams
with the Teflon seals. They are taller than the OEM seals, and leave
just barely enough clearance for the standard 3/8" lift. If you’re
planning more lift than that, you’ll have to use the viton seals.
– Kirbert
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
In reply to a message from Kirbert sent Mon 1 Nov 2010:
Thanks for the info Kirbert.
Could you comment on the seals available from the following website
They seem the right size, and a smaller build which may stop the
problems people report of the seal hitting the spring retaining cup.
If anyone knows a better supplier I would be very pleased.–
Mark Brown 71 S3 Etype
Ohope, New Zealand
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Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
5
OK, those look sweet! Y’all know I’m a big fan of Viton. And the
little coil springs around the lip will address the problem my OEM
nitrile seals had, namely that the opening had grown considerably
larger than the stem – a situation that cannot be the result of
wear, it had to indicate swelling of the rubber itself.
The only question I would have: Can they be used on the exhaust
valve stems. The OEM nitrile seals cannot, they’re fitted to the
intakes only. The Teflon seals can, I fitted seals to all 24 valves
on my '83. I know Viton is good for more heat than nitrile but
probably not as much as Teflon, so whether or not these seals would
survive on exhaust valves is a question. It’d be nice to be able to
hear from experienced engine builders on this issue to learn how
often valve stem seals are used on exhaust valves – of any type
engine – and if so, what types of materials are used. In this
particular case, the seals may actually be immersed in oil, so the
temperatures probably don’t get too extreme.
You could, I suppose, go for these Viton seals on the intakes and the
Teflons on the exhausts. Or for the Vitons on the intakes and
nothing on the exhausts. I just really don’t like the idea of the
exhausts being unsealed myself.
– Kirbert
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
In reply to a message from Kirbert sent Mon 1 Nov 2010:
Thanks again Kirbert, I have been doing some research and found the
following article from an engine builder. http://www.enginebuildermag.com/Article/2522/valve_stem_seals_materi
alsdesigns.aspx
It appears Viton can take around 450F and Teflon around 600F. I
read that the american V8’s can get to around 300F, but I’m not
sure about the V12.
Can anyone enlighten us further.
Please excuse my persistance but I only want to do this job once.–
Mark Brown 71 S3 Etype
Ohope, New Zealand
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When I tried to buy some of these the Summit racing site said they require machining of the valve guide with a special tool. Is this true for the V12 HE engine?
My car is a pre HE , so I can’t comment on the He.
Try posting on the forum
Cheers
Mark
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
9
The listing itself says this:
AFAIK, the valve guides on a Jaguar V12 are .500" to begin with, so I’m not sure why they’d need machining. But those seals look nothing like the ones I installed on my car, so I don’t really know what I’m talking about.
These are what I used on my V12, but not without an issue. The guides are the right size to begin with and the seals fit so snug they had to be pressed on, which is a good thing, they won’t be coming loose. The issue I had may be due to the cams I chose, Isky XM2s. These have a lift of .406, just a bit more than the stock .375. My problem was that I had to trim the bottom of the seals .040 ~ .060 (the bottom portion is steel, BTW) to prevent the valve spring retaining piece from touching the top of the seal. I did not test against the stock cam so it MIGHT not be an issue in that case.
Bottom line here is that they are performing fantastically without so much as a wisp of oil smoke at any time, including cold startups.
I chose Viton after using Teflon for a short time. The Teflon seals, as advertised, do NOT let ANY oil get past them. This was evidenced by one of my valves getting temporarily stuck in the a slightly down position long enough for the adjusting shim to get cocked up at an angle and stuck in that position. I found this after a teardown looking for a reason for the very low compression on that cylinder. Hence, I do NOT recommend Teflon for a street machine.
Just my 2CW, YMMV.
2 Likes
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
11
So, do these Viton seals allow any oil past to lube the valve guide? If so, is there a deliberate pinhole somewhere?
I believe it’s just due to the fact that they don’t fit as tightly around the valve stem as the Teflon seals. The Viton is very flexible and allows a thin film of oil to get by, unlike the much firmer Teflon which scrapes the stem clean.
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
13
Yeah, I find that explanation unconvincing. Those viton seals have little springs around the seal to hold them securely against the valve stem. In other applications for lip seals of similar design, you expect no leakage at all. Even if they did leak, there’s no way a designer would rely on each of 12 or 24 seals to leak enough to keep those valves lubricated; just our luck, one or two of them would actually seal and a valve would run dry. If there’s no distinct feature such as a pinhole or orifice designed to allow oil past, a designer has to presume that the valve guides will be dry.
Fact is, the same could be said for the original nitrile seals. Sure, they are garbage and don’t hold up to exposure to oil, but their intention was to seal the valve stems. Not mostly or kinda seal the valve stems, but to totally seal the valve stems. Conclusion: The valve stems are designed to run dry.
I still like my idea of applying dry graphite inside the guide and on the stem prior to assembly. Can’t hurt.
OK, well maybe my explanation is not convincing and I could be totally wrong on the mechanism at work here, but the fact that the Viton seals DO allow a small amount of oil through whereas the Teflon do not, was the basis for my choosing Viton. The difference between the two is fairly well known. Just check with anyone who does high performance head work.
Looking forward to a progress report.
Mind you, I don’t believe seals are used on the exhaust valves. I see two reasons, but others with more experience may chime in with insights.
The temperature on the valves could be a reason.
More likely because only the intake valves would allow oil from the leaking valve stems and guides to be sucked into the engine under certain conditions, mainly when the car is under engine braking towards a stop or going downhill.
