SBC 350 valve guide seals - what size, modified heads? - Team Camaro Tech
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post #1 of 12 (permalink) Old Sep 14th, 16, 02:06 PM Thread Starter
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SBC 350 valve guide seals - what size, modified heads?

I need advise on what size valve guide seals to use on a modified head.


I have a SBC 350 with a '72 block and '67 heads that I've had since 1982. I have leaking valve guide seals that I want to replace the seals. I removed the valve springs to replace the seals and found out they aren't stock. Somebody pre '82 machined the valve guides to accept the positive seal type on both intake and exhaust valves.


Also the Felpro complete engine seal kit that I bought doesn't have the correct size positive seals that fits my valves. The kit comes with positive seals and umbrella seals. I tried to fit the positive seal onto the valve and it won't fit over the valve stem.


So that's the background, what is the correct size seals for these valves? Here are the measurements for my valves.


Intake valve
.342 Stem
.528 Guide


Exhaust
.342 Stem
.502 Guide


My dilemma is I don't have any info on who built the engine or what mods they did before I owned the car. I don't know how tightly the valve guide seals should fit over the valves or the guides. From what I read, if they're too loose they leak and if they're too tight the valves will wear from lack of oil. And since they've been machined I can't just order seals to fit the part number on my heads.


Any help will be greatly appreciated.

Brian

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post #2 of 12 (permalink) Old Sep 14th, 16, 05:56 PM
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Re: SBC 350 valve guide seals - what size, modified heads?

I would suggest you locate a head shop and ask for the machined valve guide boss seals. Sometimes they are referred to as the PC seal. They are not rare. https://www.summitracing.com/parts/cca-518-16/overview/ I believe this is what your are looking for , you will need an installer also unless you trust yourself using a deep socket that fits.

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post #3 of 12 (permalink) Old Sep 15th, 16, 04:31 AM
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Re: SBC 350 valve guide seals - what size, modified heads?

Agree with Don, and don't be afraid adding a drop or two of oil onto the stem when installing.

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post #4 of 12 (permalink) Old Sep 15th, 16, 06:55 AM Thread Starter
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Re: SBC 350 valve guide seals - what size, modified heads?

Thanks guys for the input. I didn't have any idea how tightly they should fit.

Brian

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post #5 of 12 (permalink) Old Sep 15th, 16, 07:18 AM
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Re: SBC 350 valve guide seals - what size, modified heads?

Quote:
Originally Posted by b17brian View Post
Thanks guys for the input. I didn't have any idea how tightly they should fit.
They are a press fit which is why you need the special installation tool to get them on without breaking them (bending the shell). The installation tool comes with a full replacement set (or used too, I haven't installed them myself in a while letting the machine shop or head porter worry about them).

CompCams sell the milling tool(s) to cut down the valve guide boss to fit Perfect Circle valve stem seals.

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post #6 of 12 (permalink) Old Sep 15th, 16, 08:31 AM
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Re: SBC 350 valve guide seals - what size, modified heads?

Picture of guide?

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post #7 of 12 (permalink) Old Sep 15th, 16, 01:45 PM
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Re: SBC 350 valve guide seals - what size, modified heads?

When I had my heads rebuilt last year I asked the machinist to pull the studs and install threaded studs as I had roller rockers going back on in place of stock ball rockers. Also asked him to cut valve seats so I could install PC seals. He lent me the installation tool and with a couple drops of oil and a light tap or two the seals went on snugly like they were supposed to. Heads went back on and no problems since.

Just to be on the safe side however you should take the heads and seals to a competent head machinist and let him do the work. He will verify you have the correct seals and can cut the guides to fit. Good luck with your project.

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post #8 of 12 (permalink) Old Sep 15th, 16, 02:39 PM Thread Starter
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Re: SBC 350 valve guide seals - what size, modified heads?

This is a picture of the guides. The one on the right is the exhaust.

I don't have a competent machinist to take it to. Sometimes living in a small town is a big disadvantage. Also I'm not wanting to spend much money on this motor, I'm just trying to get by with it until I can replace it down the road.


Brian

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post #9 of 12 (permalink) Old Sep 15th, 16, 03:03 PM
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Re: SBC 350 valve guide seals - what size, modified heads?

If the seal shown is new, it should be pressed down on to the guide boss. That seal looks like it is expandable. Take a 1/2 socket and see if you can force it down.
These are the standard PC seals and any other seal with the same dimensions will work. They do require a special push on tool and remover but sometimes the back yard mechanic can do it in a crude way. I still have my original tool in my tool box.

If you are still confused and can't find the correct seal, either put the stock style O ring on the valve stem grove, the second one and be done with it.

The other thing you can do , is get the Ford type seal "umberella" to fit that valve and inside your spring. The O ring is cheap as well as the Ford seal.

Don
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Last edited by zdld17; Sep 15th, 16 at 03:19 PM.
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post #10 of 12 (permalink) Old Sep 15th, 16, 03:33 PM Thread Starter
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Re: SBC 350 valve guide seals - what size, modified heads?

Quote:
Originally Posted by zdld17 View Post
If the seal shown is new, it should be pressed down on to the guide boss.
Sorry for confusing the situation with the picture. That seal is the old one that was on there. When pushed down over the guide it doesn't "snap" in place. It's loose and can be pulled off easily.

Brian

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post #11 of 12 (permalink) Old Sep 15th, 16, 04:22 PM
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Re: SBC 350 valve guide seals - what size, modified heads?

Quote:
Originally Posted by b17brian View Post
Sorry for confusing the situation with the picture. That seal is the old one that was on there. When pushed down over the guide it doesn't "snap" in place. It's loose and can be pulled off easily.
I thought so, So its simple, just order seals from the link I first sent you , or go down to a part store and look for these seals.

I believe the kit will have the correct installer tool. Worst case, go back to the O ring in the second grove.

Don
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post #12 of 12 (permalink) Old Sep 19th, 16, 08:31 AM Thread Starter
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Re: SBC 350 valve guide seals - what size, modified heads?

Thanks Don for the link and advice. I'll order those seals from the link you sent and try those.

Brian

'67 SS/RS 350, Muncie M20, Black with black interior.

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