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Old 10-25-2009, 07:41 AM
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Positive stop Teflon Oil Seal question

Greetings all,

I have a question about using positive stop seals. I have an Olds 455 that I am building and have gotten into a situation where I need to use Positive stop seals. I am using stock heads and I'm getting ready to have the valve guides machined to accept the seals. The question I have is whether I need to install the seals on both intake and exhaust or just intake. I spoke with a local machine shop/ engine build shop and they recommended using the seals on the intake only. That putting the seals on both would restrict to much oil from the valves and potentially burn the valves up. This sounded a little odd because I thought the purpose of these seals was to keep oil from getting into the combustion chamber. However, I am a novice at building engines and figured there were more folks out here that might know the answer. The set up I'm running is stock heads with double springs, which is why I've been driven to the positive stop seals. Any insight would be greatly appreciated.

Thanks,
Rob

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Old 10-25-2009, 10:01 AM
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First you have to understand that there is Vacuum present on the intake guides that tends to draw oil down into the combustion chambers. But, on the exhaust side there is pressure. This tends to try to blow the oil back up the guide.

On older style engines I tend to use positive seals on the intakes and Umbrella or deflector seals on the exhaust. This allows better oiling to the exhaust. There are lots of arguments on this subject. Most citing the modern engines that use positive seals on both intake and exhaust. But, these engines were engineered for such use and have different exhaust and intake guide/valve materials. Not just plain old gray iron like the older stuff.
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