I have looked at the various options and I wish to stay away (for the moment) from machining guides. So I bought these from Crane last autumn. Now I am confused. From what I have read there are umbrella and positive seals. These look like they fit on the valve stem but apparently are umbrella seals. Is that correct? Do they just ride up and down on the stem? Do they work? I thought the ideal would be a positive (stem-mount) seal that would not require machining. But I cannot find those. Finally, GM just used o-rings in 1979 so I do not know why this is all necessary. I do have an oil consumption problem and that is the basis of my question.

 

I just ordered a set of Crane Cams street umbrella seals. They don't require any machining. http://www.jegs.com/cgi-bin/ncommerc...517&prmenbr=76 I'm not sure how they work though. You did yours not work?? There the same part number I ordered.


[Modified by Aaron-74, 8:49 PM 2/20/2002]


[Modified by Aaron-74, 8:50 PM 2/20/2002]

 

OK, in various years GM has played around with valve stem seals....earlier cars sometimes had 'umbrella' stem seals and most later one's do....but sometimes just on the intake valves....leaving just that O ring under the keepers wedged into the retainer .....
the exhause umbrells seals ride up and down onthe exhaust valve stem...apparently....but the intake valve similar seal just lets the valve stem slide through it, while fastened/clamped to the cyl head/guide....
I think it has something to do with valve stem temps and cooling/melting the seals....

I just know that most engines without BOTH unbrella seals and of course the O rings up top....will burn oil or startup at minimum ...as soon a guides get a bit worn....50k miles or so....

so when I build heads...use all 3.....sometimes they only ship the intake umbrella seals, with O rings....8 and 16 count.....instead of 16 and 16 count..
cheap illegitimates....

GENE

 

Those are umbrella type seals that ride with the valve and shield the guide from oil running down the stem like a.. uh.. well ...umbrella :smash:

 

Does that mean the exhaust and intake seals are different? Or for the Crane examples shown above (all 16 are the same), you let the exhaust ride on the stem and for the intake, you push it over the guide? And you use o-rings for additional insurance?

 

You see the two metal snap type rings around the seals? These seals slip down over the cyl head at the valve stems and are held in place by the spring clips. They do not ride up and down on the valves at all.

 

Yea, that's what I thought also, but Crane says no machining so that means they'll fit any size guide? :confused:

 

MasterDave's right on this. There are three basic types. Stock is the "O-ring" type that fit inside the valve spring retainer, under the keepers. They form a seal to keep oil from running down the guide into the engine. The second type (which you have) are "positive" seals that slide over the guide and do not move up and down with the valve. Some of these are just rubber, some have springs at the bottom, some have teflon inserts in the seal itself. These are the best. The third type is the "umbrella" seal that fits tight to the valve and rides up and down with it. As a rule of thumb, as the engine ages, the oil is consumed through the intake guides (thats where the vacuum is) while running, and runs down a loose guide when shut off. If the stock O-ring seals are hard and cracked, or the guides are worn, it allows oil to do this and causes that puff of light blue smoke at cold start-up (usually after sitting overnight). When I build stock street engines, I use o-rings and positive seals on the intakes, and just the o-rings on the exhaust valves. I actually like a slight amount of lubrication on these. There is always positive pressure on the exhaust side anyway. On a used engine that has loose guides and smokes on start-up, I use both types on intake and exhaust.

You mentioned "machining" the giudes for seals. I used to use that type of positive seal (made by Perfect Circle, among others), exclusively, but now only on high performance engine that get frequent tear-downs. These are teflon and are driven on the machined guide. A very tight fit.
Hope this helps.

Hans

 

I believe Crane assumes a standard/stock guide size. The seals shown are sold as 11/32" which is the valve stem diameter. For oversize valve stems, there are other offerings.

 

Ok so these are for stock size guides, springs etc...gotcha :cheers:


[Modified by yellow 72, 10:41 AM 2/21/2002]

 

In many applications there are no valve guide seals on the exhaust valves because of the exhaust heat on the seals the seals wouldn't last long at all.Which is possibly why they use an umbrella seal that rides up and down instead of a fixed seal.

 

Maybe it's just me but those look like positive seals to me. That means that you WOULD need to machine the guides in order for them to work correctly. If you have the heads off of the car, that isn't a bad thing to do and isn't that expensive. If the heads are on the car, you need the umbrella type which require no machining. I think Crane sent you the wrong part (positive instead of umbrella).

I could tell you for sure if the pic was bigger or if I could hold one in my hand. :jester

Hope this helps.

dl


Revision: Upon looking at those seals on the Jeg's link above, they do look like umbrella seals although I have never seen any with the snap rings around them. All the ones I have seen were just rubber with no metal parts. The ones you have should fit on the valve stem with no modification to the guides at all and will ride up and down with the valve. They sure did go out of their way to make them look like positive seals though.

dl


[Modified by dladd74roadster, 1:09 PM 2/21/2002]

 

Not wanting to consume oil, last buildup I did this:

1. Machined the valve guide ends. It's really quite easy with a bit and drill motor.
2. Installed teflon PC seals.
3. Installed umbrella seals (on intake valves only).
4. Installed the O rings under the keepers.
5. I vow to use only Mobil 1, which doesn't sludge, in my engine.



Yep. Two different types of seals at the same time + O rings. The umbrella seals just slip over the teflon seals and inside my 3 piece springs. I believe they go up and down with the valves and keep the majority of the oil off the teflon seals, which keep the majority of what hits them out. Seems to work.



Considerations:

Intake valves operate in a negative pressure environment (i.e., manifold vacuum). Thus the need for better sealing on the intakes, lest oil be drawn into the guides.

Exhaust valves are HOT. Rubber umbrella seals on them might cook.

Sticking valves occur due to deposits forming on the valve stems or in the valve guides. I use only Mobil 1 synthetic oil, which is known to form very little sludge.

-Noel


[Modified by Noel Carboni, 7:31 PM 2/21/2002]

 

Here is a close-up.
http://temp.corvetteforum.net/c3/pau...mseals_003.jpg

 

Noel,
I appreciate your post but there must be a solution without taking the heads off.

 

No problem Paul. I wasn't posting an end-all answer for you so much as just info to help enlighten the huddled masses. :)

Be careful when taking the springs off that you don't lose a valve down the hole.

Just thinking... You *might* be able to cut the guide down if you carefully turned the crank to let the valves recede part way into the guides. The guide end of the cutter isn't all that long, as I recall. Of course, you'd have to be really careful where you let the metal fragments go.

-Noel

 

No worries Paul. You can do it on the car. Those seals will snap right down on the stock head with no machine work. I have done it enough times to know. You ought to try it in C4 with a TPI manifold, EGR tube, and everything else in the way.

I use a long magnet, spring compressor, home made hose from a ant-foul spark plug kit and standard air comrpessor hose and quick disconnect.

I pull the valve covers, pull the plugs and rocker arms with push rods. One at a time, screw the air hose into the plug holes, then quick connect about 75-100 psi of air on the line. As soon as the cylinder is pressurized, use the compressor tool to compress the valve spring, and the magnet to grab the retainers.

Now pull the spring off, clean around the valve stem, removing the old crunchy O-ring. Install the new seal with plenty of lube and if you want, use a 1/2" or so deep socket to tap it into place. Return the spring, install the clips, and release the spring pressure. Now, gently rap on the valve with a hammer to make sure the retainers have snapped into place. Move on to the next valve. Then, release the air from that cylinder.

Just do this 16 times and you are finished. I usually install the hard cone type umbrellas on the exhaust, and the rubber with two rings on the intake. However, I have seen where both intake and exhaust have the same seals.

Good luck.

 

Thanks. But with the Crane seals pictured, do they go on the guide or just sit on the valve stem?

 

Paul,

They just kind of pop onto the stub that comes up from the head where the valve stem goes through. When you tap them into place, they stay put.

It will look kind of strange at first, but no worries.

I am not sure Crane really makes those anyway. Do they have a PC stamped on them? If so, they are the same that you will find in Felpro, G.M., etc.