I am going to replace the valve seals in my 76. I am confused as to what type to get. Viton, positive seal, intake different than exhaust, do I need o rings too? Any info would be much appriciated.

Thanks,

mike

 

Mike -
The stock seals are the simple square cross section O-rings at the top of the valve stems. Unless your guides are worn, these seals work fine when used with all the stock retainers and splash shields.

You cannot install the PC Viton seals without machining your valve guide bosses to accept the seals - the PC seals cannot be installed onto the bare casting bosses.

Lars

 

Thanks for the reply Lars,
The valve job is only 3k miles old valves and guides were replaced so theguides should still be ok. I'm getting an occaisional puff of smoke on start up and going through a qt of oil in 400 mikles. So just O rings? what about umbrella seals as well?
Mike

 

Lars, I thought that the PC seals were Teflon...? I used them back in the 60's and did have to machine the valve guide bosses to install them. Generally speaking the Viton seals will slip over normal valve guide bosses with little difficulty and no machining. Here's a typical PC Teflon seal...


Here's what a typical Viton seal looks like...



If you measure your current valve guide bosses, you can purchase the Viton seals in a number of different sizes to fit most stock guide bosses. Because they are much softer than Teflon seals, their fit isn't nearly as critical as it is for Teflon ones.
http://www.jegs.com/p/COMP-Cams/Comp...22701/10002/-1

I have never personally been a fan of the "O-ring" seals GM used, probably because I've never removed one that didn't disintegrate in my fingers. On the other hand Ford seemed to always use the rubber umbrella seals and while I've found a few that were pretty stiff, they always seemed to do a better job and last much longer than the GM "O-ring" seals. Interestingly the Chevy Vega's came with a very nice Viton seal that worked well on SB Chevy's and I've used them frequently with great success in the past. They seem to be hard to find these days however, although Fel Pro does have a listing for them.

The most important thing is to be sure to use the "valve stem protector" (slips down over the end of the valve stem) when installing the seals to keep from nicking the seal as it slips over the groves in the end of the valve stem that hold the keepers.

Good luck... GUSTO

 

The new PC seals are available in a variety of materials - the "first generation" were Teflon (PTFE) as shown in your photo. The PC seals are now available in the original PTFE design, as well as Viton, Nylon, polyacrylate, and a Dupont Fluoroelastomer similar to the Viton. Additionally, the "umbrella seals" that you show as the black seals in your photos are now also available in PTFE (Teflon), so there is a huge combination of seal types and materials available for the seals. The seals known as "PC" seals are the ones that typically require machining of the guide bosses. The seals that I call "umbrella seals" are the ones that slip over the existing cast guide bosses. These seals come with or without a spring clamp around them (as shown in your photo).

Lars

 

Mike -
If your valves/heads were assembled with only the top, o-ring stem seals, the springs need to have the metal shields installed on them to prevent direct oil splash onto the valve stems below the o-ring. Many builders will delete these spring shields during assembly. If you're having extreme oil consumption, verify that the shields are in place and have not been deleted.

The stock system with the O-rings and shields works just fine if there are no other issues. If all the parts are there, and the O-rings were not damaged on installation, you should not have to Band-Aid the installation with umbrella seals. Look for other issues if all the seals and shields are correctly installed.

Lars

 

Thanks again lars,
I will look this weekend. I Know the springs are comp cams matched to the cam so who knows. I will check this weekend. What do the sheilds look like and can I see them through the spring? If they are missing would you suggest installing new O rings and sheilds?

Mike

 

The shields are installed over the outside of the springs - they cover the top 1/3rd of the springs. If you can see the springs and nothing is covering them, you don't have the shields.

 

Thanks Lars, Now I know what you mean, considering they are aftermarket springs I would say the sheilds are long gone. So what would you do for valve seals at this point if you were me? Its as clear as mud now.