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Old 05-13-2008, 09:08 PM
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Valve Seals

I am wanting to use these valve seals on a pair of sbc heads that I have. Are these good seals to use?

I think the blue one is called a "positive seal", correct?

Is the other an umbrella seal?

I have seen some like this that have an o-ring with it. Do I have the right ones? TIA!
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Old 05-13-2008, 10:25 PM
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Quote:
Originally Posted by stfinney
I am wanting to use these valve seals on a pair of sbc heads that I have. Are these good seals to use?

I think the blue one is called a "positive seal", correct?

Is the other an umbrella seal?

I have seen some like this that have an o-ring with it. Do I have the right ones? TIA!
Which seals do you want to use?

Yes the blue one is a positive seal the yellow one is an umbrella seal. They work differently. The positive seal requires the upper guide be machined to fit it. It clamps rather tightly and the portion that rides against the stem actually wipes the oil off. They are particularly good on the intake where the manifold vacuum is always trying to draw oil down the stem, which can lead to too much oil passing the stem and getting into the intake at the valve.

The umbrella seal isn't really a seal, it catches the oil flying off the valve train parts and diverts it away from the stem and guide area to reduce the opportunity for oil to be drawn down the stem and guide. The umbrella seal works better on the exhaust as there is pressure always trying to push oil out of the guide, since it admits more oil, it provides a greater quantity to the guide.

The O ring that GM uses is to stop oil draining off the retainer and locks from running down the stem into the guide, it is probably the least effective, but works pretty well when the stem to guide clearance is new and not so well as these parts age and wear.

Given all my druthers, I prefer to use a positive seal combined with bronze alloy guides as the bronze requires a lot less lubrication than cast iron against a hard chrome stem. But this is a personal preference not a 'have-to' because somebody says that's the way it is.

Bogie
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Old 05-14-2008, 06:23 AM
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Does that mean my stock heads will have to be machined for these positive seals to work? I just want good seals for my heads. Don't really care what type, just as long as they do their job!
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Old 05-14-2008, 06:27 AM
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The seals shown are the type GM used on factory heads produced from the mid eighties till the Vortec series. The seal with the ring, fits the intake valve side, with no machining and the white nylon type seal goes on the exhaust valve stem. Later factory heads did not use the early type o-rings.
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Old 05-14-2008, 06:32 AM
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Ok, so the seals that I have will work good just like they are? I am trying to learn more about head assembly, so thanks for your help.
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Old 05-20-2008, 10:21 AM
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Well, I am not the only one in trouble chhosing the right seals for the right heads, hopefully good advices like oldbogie and some others are helping a lot!
For instance, about the positive (viton) seals which goe on intakes, I lack the perfect answer about their installation on my 305 (1978)heads (casting 378450). I found these heads are 78/85, and the exhaust guides size seems ok for that kind of seal installation, but I am still not sure, if anyone can help me....
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