Valve Stem Seals

[DRACO A5OG]

I had a brain fart this morning.

I want to swap my valve stem seals "WIAIT" swapping my cams.

Have you guys notice difference in wear from upper to lower seals? I know in the JDM crowd the tend to use different material in the exhaust stems to help reduce heat wear. I am wondering if I just replace the lowers to OEM 964 ones not the white teflon as I read they can be too restrictive of needed oil for the stems?

Any input would be most grateful

This is for preventive measures, as I am consuming oil but I have to attribute at least half of it due to leaking rocker shafts, and failing o-rings. Oh yeah will be doing this with boobies on the heads. Yes, I know not the right way but I really do not want to break the tower to head seal and risk miss-alignment upon install, I do not trust myself.

Will be doing leak down today,

[Trackrash]

I am toying with the idea of leaving off the lower exhaust valve guide seals. I read somewhere here that someone does that. The theory is the exhaust valves need oil, and there is no suction from the exhaust to pull oil into the cylinder. Hell, VW T1s don't use them at all.

Be interesting to hear what the experts have to say.

[DRACO A5OG]

Hmmmm? That makes total sense.

I can leave the old one on the exhaust side and swap the uppers. Love it

The pros must be sleeping or ignoring us :-P

[chris_seven]

Be very careful about deleting the exhaust valve guide seal, it is not something I would consider doing.

The 911 engine uses a positive seal which fits to the valve guide.

Its action is designed to squeegee and wipe and meter oil onto the valve stem as it moves through the seal.

You should also consider that as the exhaust gas leaves the cylinder it does create a vacuum in the guide and will draw oil though the guide and into the exhaust and oil consumption can increase significantly if seals are not fitted and guides exhibit some wear.

[DRACO A5OG]

Noted sir, Thank you so much for posting! Most grateful :-)

[cgarr]

I have seen a small oil passage machined to the exhaust guide for oiling but never tried it, maybe more for race motors. ?


Sent from me

[Trackrash]

Originally Posted by chris_seven

Be very careful about deleting the exhaust valve guide seal, it is not something I would consider doing.

The 911 engine uses a positive seal which fits to the valve guide.

Its action is designed to squeegee and wipe and meter oil onto the valve stem as it moves through the seal.

You should also consider that as the exhaust gas leaves the cylinder it does create a vacuum in the guide and will draw oil though the guide and into the exhaust and oil consumption can increase significantly if seals are not fitted and guides exhibit some wear.

Makes sense to me. IF I can find that other post, I'll link it.

[DRACO A5OG]

Just wondering if any of you have mixed the Stem Seals with Teflon and 964's (OEM) and where you placed them?

[Trackrash]

Originally Posted by Walt Fricke

Why bother with seals at all on the exhausts? Not much negative pressure acting on them, is there? And the oil has to go uphill.

Here you go.

Originally Posted by cstreit

Slighty OT in this thread but...

I used the white teflon ones recently and found that despite the popular opinion of them allowing more oil for better cooling of the valves, they actually dragged on the valve more and appeared to offer less oiling.

In addition this particular motor had a very high lift cam and the taller teflon ones were getting hit by the valve spring retainer... So we had to use the viton ones on top, and used no seal on the bottom... (race motor)

[DRACO A5OG]

Well, that settles that on the white Teflons

[KTL]

I would use the brown, not the white. Saw a picture from a set of heads that cgarr was doing for a local friend of mine. The wear at the end of the valve guide was massive. "Could drive a truck through it" came to mind. Really, the amount of clearance between the valve stem and the guide bore was huge. The end of the guide looked all ratty & "hogged out" it was so worn.

[DRACO A5OG]

Outstanding, ordering them now :-)

[Trackrash]

Found it.

Originally Posted by Walt Fricke

Lubrication of the exhausts can be improved, I think, by omitting the guide seals. No suction in the exhaust port to speak of, and no gravity to help move the oil along. I can't say I have done SAE quality testing, but have not noticed any excessive oiling issues with the motors I have assembled without them.

from this thread, Valve stem finish & valve guide wear

[chris_seven]

When we first started competitive rallying we ran small rear engine 1 litre cars using a Coventry Climax based engine.

These units ran at 10 000rpm and with race cams fitted there was just no room for stem seals on either the inlet or exhaust valves.

On a good day driving on roads you could get an oil consumption of about 500 miles per pint using a 20W/50 such as Valvoline Racing.

On competitive events using all the revs a fresh engine used oil at a rate of 100 miles per pint

They were never particularly smokey but they just used to use oil.

These were wet sump engines and we always fitted large capacity, baffled sumps.

The standard road cars with seals and much lower performance used about a pint between the 3000 mile oil change interval.

The engine was an SOHC unit and we always used to fit an external oil drain from the head/cam carrier.

The engine used to lie on its side on the car and at idle the guide area filled with oil unless there was a drain and if this mod was not carried out they smoked badly.

I would think that a 911 without seals may not smoke but oil consumption is quite likely to increase.

On a race car this is OK but on a road car could be a pain.

[Mark Henry]

Another thing you can do is to cut a small V notch in the seal lip.

[Walt Fricke]

I've always left off the exhaust seals on my race motors. I did so because the engine builder who guided me through my first race motor builds said that was the way to go. It has never caused problems on the race motors. And I can't recall how I approached this when I rebuilt my SC stock/street (though raced) motor in 1999 or so, though it does not have excessive oil loss through the guides (frustrating leaks are a different matter).

Chris has a far better background both by education, professional experience, and race engineering experience than I have (which is none, really), but I have trouble seeing that, on a 911, the negative pressure in the exhaust port you would like to see due to header design to help suck some more air in as the intake overlap develops is going to be anything like the negative pressure in the intake port when you close the throttle (especially when shifting at high RPMs, or jumping on the brakes on a track.

I have on occasion wondered if it would be useful to take a pair of valve covers (like ones with holes where they shouldn't be from engine explosions), and fitting a piece of glass or clear plastic so you could see what the oil was doing on a running engine. I know from this list what happens if you try to look with no valve cover, and what one would learn from that experience is only that it was a mistake. But it would be interesting to know just how much oil accumulates up there, how well the two large return tubes do their job, and whether cornering Gs (here the now cheap cameras would come into their own) tend to fill up one side.

The drilling Craig may be remembering might be the hole in the 935 heads which led oil down to the lower part of the exhaust valve guide. But I think (all I know is from the picture and description in Bruce Anderson's 911 book) that drilling sent oil to the outside of the guide still within the head, and cooling was its purpose. Not clear how a small one way hole would do that, but Porsche did it.

[Mark Henry]

Originally Posted by Walt Fricke

I have on occasion wondered if it would be useful to take a pair of valve covers (like ones with holes where they shouldn't be from engine explosions), and fitting a piece of glass or clear plastic so you could see what the oil was doing on a running engine. I know from this list what happens if you try to look with no valve cover, and what one would learn from that experience is only that it was a mistake. But it would be interesting to know just how much oil accumulates up there, how well the two large return tubes do their job, and whether cornering Gs (here the now cheap cameras would come into their own) tend to fill up one side.

I know for sure the VW bug guys have done this and the valve covers fill 3/4 of the way. Aircooled VW's don't have guide seals, never have.

[Walt Fricke]

Grady Clay once mused about using scavenge pumps to evacuate the excess oil from above the heads. But I don't recall his rationale as to why this would help make more power or otherwise be beneficial. Hard to imagine anything like the pumping losses from the reciprocating and rotating parts inside the case, nor possible ring seal benefits from negative pressure there. But Grady knew a lot, and was very creative.

[Flieger]

I think the GT3 has scavenge pumps in the heads. I think it started with the 962 or at least the GT1. Necessary for sustained lateral g's.

[Walt Fricke]

Now that you mention it, I think that was the rationale. I don't know if you can sequester so much oil over there that you run short on oil fed to the pump, but maybe that much oil does cause too much to get into ports? Or without it circulating as much there is less head cooling?