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Old 03-06-2011, 08:32 AM
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SBC Positive Valve Seals

Quick question- I purchased a set of Felpro SS72527 for my SBC, and am installing these on my heads. They fit fine on the guide, but is there some trick to getting the metal band to 'crimp' or lock the seal more securely down on the guide?

THANKS in advance!

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Old 03-06-2011, 02:02 PM
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Rubber seals

Those are specifically for 1981-1993 Chevrolets and are stock replacement rubber umbrella seals designed for the intake valves only. The stock exhaust valve guide boss is not machined to fit those seals.
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Old 03-06-2011, 03:44 PM
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I was under the impression that they were positive seals since they fit tightly over the guide. They don't even look similar IMHO. I'll see if I can upload a shot from my phone.
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Old 03-06-2011, 04:15 PM
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Old 03-06-2011, 04:25 PM
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Don't those valve stem seals require a machined valve stem boss?

Vince
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Old 03-06-2011, 04:47 PM
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They're OEM replacement for my 416 castings is how I understand it....

Here's a shot of the destructions- it just says on the back side to press them over the guide but nothing in regards to securing them further unless its a later model metal design...

Also, the guides already appear to be machined- at least the intakes. Ill pull an intake and exhaust spring and get a shot either tonight or this week.


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Old 03-06-2011, 05:31 PM
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Seal springs

Teflon or Viton positive stop seals are installed on a guide boss that has been machined to 0.530" diameter for a 0.001" interference fit and the seal bottoms on the valve spring locator boss. The stock Chevy spring locator boss is generally about 0.900" OD and must be machined smaller for dual valve springs. The Teflon and Viton positive stop seals has a spring that tightens on the valve stem and a spring that tightens on the valve guide boss and must be used with dual or triple valve springs. The one you have are Viiton rubber umbrella seals and they do not have a spring that tightens on the the valve stem.

Umbrella seals allow a small amount of oil to pass into the stock iron valve guide for valve stem lubrication. Virtually no oil gets past Teflon or Viton positive stop seals and that is why you should install K-Line Bronze Bullet (or equal) phosphor bronze valve guide liners to use those type positive stops seals. Bronze guides or guide liners have "self lubrication" characteristics.
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Old 03-06-2011, 06:06 PM
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There's no additional crimping supposed to be required- they're pressed onto the guide boss on heads that have an OEM machined guide boss upper OD. Just be sure to use the plastic protector over the valve stems to keep the seal from being damaged on installation.

I have heard of these seals being cemented to the guide boss, but have no experience w/doing that myself.

Be sure to use the O-rings in addition to the seals. Install them w/the spring compressed.
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Old 03-06-2011, 06:32 PM
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Those seals are used on the intake side of most SBC's since the mid seventies. They will tollerate quite a bit of variance in stock valve guide OD. They will not fit a .500 OD. guide. They fit a stock quite tightly. I use an install sleeve and a plastic hammer to install. These do not need any glue. The steel expander ring does an excellent job of retention. Use an umbrella seal on the exhaust. The factory continued to use the O-ring seal with these, till the nineties, when the O-rings were no longer used with these seals.
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Old 03-06-2011, 06:47 PM
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Quote:
Originally Posted by cobalt327
There's no additional crimping supposed to be required- they're pressed onto the guide boss on heads that have an OEM machined guide boss upper OD. Just be sure to use the plastic protector over the valve stems to keep the seal from being damaged on installation.

I have heard of these seals being cemented to the guide boss, but have no experience w/doing that myself.

Be sure to use the O-rings in addition to the seals. Install them w/the spring compressed.
What kind of cement? RTV? Im being careful to use the install sleeve each time.

Bob- I have a couple that are pulled off theguide boss easiee than others, but you are correct that they fit pretty tight! So far they've just slid right on no mallet or socket required.
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Old 03-06-2011, 07:29 PM
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What heads do you have and have the guides been cut for seals?

Aftermkt heads and machined heads are usually cut for .500 or .530 seals. The Fel-Pro blue seals are not for these guides.. These guides take seals specifically designed for size. The glue on seals are in this category. Hylomar glue is used on guide/seal surfaces.
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Old 03-06-2011, 08:02 PM
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They're 416 castings. After I ported them, I had them cut for 1.94 intake valve, new bronze guides, and Manley SS Race or Street Flo valves- I don't remember which, just that they're undercut and swirl polished SS.

I honestly don't know if they've been cut for seals- they looked machined, but I didn't mic them, and don't remember if that's something the machine shop did or not.
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Old 03-06-2011, 08:44 PM
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Bronze guides or liners? Bronze repair guides are usually .502 od. Too small for Fel-Pro seals.
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Old 03-07-2011, 09:54 AM
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That's a great question- I'd imagine liners since the valve guide boss is not bronze.

Hopefully I'll get some time out there tonight or next few days where I can pull the I and E springs and get a picture.
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Old 03-07-2011, 10:53 AM
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Quote:
Originally Posted by HawkZ28
What kind of cement? RTV? Im being careful to use the install sleeve each time.

Bob- I have a couple that are pulled off theguide boss easiee than others, but you are correct that they fit pretty tight! So far they've just slid right on no mallet or socket required.
I seem to recall weatherstripping cement being used- but nothing need be used on these particular seals unless they were sloppy-loose. Unless the guide boss was poorly machined from the factory or it was done by a PO, this shouldn't be the case.

As a check, you could simply measure the seal ID and compare that to the boss' OD- the seal's ID has to be smaller than the boss OD. As long as the amount of pressure holding the seal on the boss exceeds the valve stem's friction to the seals, you're good.

If you're careful, on the loose seals you can remove the split bottom band and tweak it to be a little tighter. What you do NOT want, is to crimp the retainer, or make it oval, or to be so tight as to deform the seal.
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