I am in the process of rebuilding my 350 motor and have been working on some replacement heads from a 79 , I decided to use these to allow the use of unleaded gas .
These heads had the cap type seals over the valve guides but the new head kit only has the small "O" rings for the groove below the collets.
Will the small "O" rings be sufficient or do I need to source a set of the cap type seals as well ?? .

Mike .

 

There should be nothing wrong with the "O" rings seals if your guides and stems are in dimensional spec.

 

I think the little orings you're describing will be what I end up with on my 67 L79. The engine builder was talking about a newer style of seal that was fixed to the pushrod, instead of being fixed to the head. He said they were more reliable.

Sorry I can't provide more detail than that. I'm still getting into the motor at this point.

 

Better oil control can be had by using the Viton (but never the Teflon versions for street usage) type PC seals on the intake valve stems only. PC seals are inserted over the guide (which must be machined to fit them). These are marketed by Fel-Pro, Perfect Circle, and K-Line, among others. But keep the "O" ring seals on there as well (if the valve stems have the grooves for them).

The main issue with using just the "O" ring seals is the amount of oil flooding the stem/guide is a function of oil splash in the valve train area. The more splash, the more oil flowing down the stems. Adding the PC seal limits this over abundance of oil. Even Chevy changed over to them.

Using the PC seals only on the intakes prevents the typical coking of oil on the backside of the intake valve head. The exhaust valves run much hotter, and will burn off any excess oil, and the exhaust stems/guides can use the extra oil flow.

Stingray1967,

The seals your engine builder was speaking of were umbrella seals that go onto the valve stems (not the push rods). These are better than just the "O" ring seals, but are no where as effective as the PC seals. If the PC seals are of Viton material, they are very long lasting (that is what GM uses). It is the Teflon versions that are cheap and short lived.

Plasticman

 

Plasticman, can you translate the "PC" acronym for me?

 

Thanks for all the info I now have a far better understanding .

Plasticman - you mentioned umbrella seals , are these similar to the pc seals but fit non machined head ? My head has champhered type top to the valve guide in in head with straight sides , would umbrella seals fit and if so is it worth the bother of removing and refitting the valves just to fit them ? my heads are still off the block so now is the time .
Cheers
Mike .

 

Perfect Circle - The Brand name of the seal

 

Mike,

Umbrella seals are slipped over the valve stem and float up and down with the valve. The umbrella portion extends down over the guide boss, but does not seal to it. This is where oil get back onto the stem, and the reason it is not as good as the PC seals. Also, if you are using double springs, there may not be room for the umbrella seals.

Since you have straight guides with the chamfer, sounds like they are set up for the PC seals already. Mic the diameter of the guide boss to see if it equates to the PC seal ID. I am out of town, and don't have the info on what diameters are avalable, Check the K-Line website or perhaps Fel-Pro and see if your guide boss diameter matches to their products.

I would add the seals. It will pay in the long run. Even the umbrella seals would be better than just the "O" rings.

Here is the K-Line web site listing for seals. Notice that seal dia. come in .500", .530", and .562" (for standard 11/32" Chevy stem diameters).

http://guideliner.net/index.php?zeni...eals&x=19&y=12

I see that K-Line is now using a "Special Teflon Sealing Element". I have not used those seals, and will have to make some calls to find out why they changed the design, and how that affects the life of the seals.

Plasticman

 

Heads up guy's!!!

Let me see if I can help clear up some issues in this area. It crosses over the line between OEM units, street/performance units, and "track-only" ones.

I'll go back to the "original" "O" rings from Chevy. These pieces were designed to function ONLY when the guides are in excellent condition.

When the guides are "new" they are able to control the total amount of oil required between the stem and the guide WITHOUT a positive type seal installed directly on the top of the guides to make it all work correctly. The "O" rings only function when the unit's not running. They stop the oil that collects at the top of the lock/retainer area when the unit is parked, the oil that has collected up there CANNOT get past the "O" ring to "run" straight down the stem on to the back side of the valves. The "puff" of smoke that you are seeing, as the guides begin to wear and only have the "O" rings in position, is from this oil that has run down from the stems while parked.....

As any appreciable amount of wear that begins between the guides themselves and the stems, these seals are "along-for-the-ride". They do nothing at this point in time!

Now, "track only", you have the 1 piece teflon "PC's". These were designed to function where the vacuum signal was low, from large camshaft's, or non-existent, at wide open throttle.....the guides are machined for a press fit with the seals. One type of "positive" seal. There ARE many others.

Now comes the "street-n-strip" setup, this is mostly the seals we are using on most of our street builds presently. It DOES have a "Teflon" insert incorporated into a "neoprene" housing that actually "floats" in the rubber surrounding it. These seals are also "pressed" on the guides which means the guides must be machined also. Either for a .500" OD or a .530" OD. There are other sizes but these are the most popular ones. They fit both the .343" SB stems and the .375" BB stems according to the part numbers.....

This is a very unique seal, it has a "built-in" oil control system by design, remember I stated that the Teflon "floats" in the rubber housing on this one. What it does is sense the vacuum signal at the intake stems. The higher vacuum it senses actually causes a tighter fit between the Teflon and the rubber housing, if it senses lower vacuum it allows the Teflon to relax in the rubber housing thereby allowing the correct amount of oil into the guide at the right time. An important factor here to remember with Teflon is that it has excellent wear characteristics. It will not wear away over time AND it will not wear the stems either.

Hope this helps some up here.

Thanks, Gary in N.Y.

P.S. There are MANY other seals and variations in the marketplace, BUT, doing over 300 units per year, we have NO issues with respect to oil control, we don't even pay attention to it anymore! It's pretty much down to a science now!!!

 

If the new heads are like the ones from the 60" and 70S a TRW part number "VP-24" fits over the valve guide boss tightly without machining. They are like a PC seal but you do not have to machine for them. You can run these with the O-rings. You only need them on the intakes because the exhaust do not see vacuum that pulls down the oil. Just run the o-rings on the exhaust. 20 years ago they were only about $ 0.25 each. Just another option.