Valve Seals: How Do They Work?

This has been bugging me the whole two weeks AT+T has been screwing me over making me wait to get this dial up line fixed.

Valve stem seals are not actually "seals" because they have to allow some oil flow down to lube the valve shaft in the guide. How are they designed to "leak" the proper mount of oil? As far as I can see, they have a tight fit on the valve stem. I don't see any hole or groove to seep oil. There is just the rubber ring with the spring around it for tension.

Do all valve seals leak a controlled amount of oil?

Is it normal to have some oil seepage down into the combustion chamber (from the valve guide through an open valve) after the engine is turned off?

I would like to understand how the seals are designed to work.

I'd ask at www.aperaceparts.com , www.kzzone.com or www.fastbygast.com These guys rebuild engines and can answer your question better than most people can.

The way I understand it is that they ARE supposed to keep the oil from getting down the stem at all. Any stem lubrication is supposed to come from the incoming charge...
at least for the intakes.
The tolerances are made to take all expansion into account so there's no stem-to-guide seizure and also the fact that there's no lubrication.
I just overhauled a brand H tiddler and the valve stems both looked great....but they were worn below spec. The intake had a seal but no seal is fitted to the exhaust because none
is needed, apparently. The guides were still within spec...barely.
So....new valves and new seal on the intake and away she goes.

Think Gasoline!!!!

It use to be tetraethyl lead that turned into lead oxide as it burned. The layer of lead oxide, would cover the valves and the combustion chamber. The valves hit hard against the valve seats several thousand times each minute. The lead oxide acted as a cushioning agent, and protects the valve and the valve seats. The lead oxide was also a lubricating agent. This reduced wear in the valve guides, as the valves slide inside them.
Now there are other additivies in gasoline that act as lubricating and cushioning agents for the valves, seats and guides.

Or so I've been told.

Buzz

Plus the guides are bronze or brass, against steel they're a good low friction bushing. I've machined brass bushings for things that work just fine over a long term with no lube. For things without a lot of load on the wear surface, like a valve guide, it'll last a long time.

Right T_Dub and in the case of the KZ engine there's very little side loading on the valve stem because there are no rocker arms to push the valve against the guide. The DOHC design with the cam followers directly under the cam pushes the valve straight down.

Buzz

Interesting replies. So, the best seal is the one that seals oil the best?

I was trying to figure out what is the typical "failure mode" for the seals. I have the four old seals (and old valves) from before the last rebuild and three of the four seals still feel pliable and tight on the valve stems... yet, they were all leaking oil like a real sob. I had one seal that was torn at the top so it was REALLY dumping oil, but the others were also leaking down into the combustion chamber and they don't look like they should have leaked.

KruZer wrote:

Right T_Dub and in the case of the KZ engine there's very little side loading on the valve stem because there are no rocker arms to push the valve against the guide. The DOHC design with the cam followers directly under the cam pushes the valve straight down.

Buzz

That's what the machinist who did my head also said. I bought a new set of guides since the engine had 75k miles, and he showed me that all the original guides were as tight as the new ones so they didn't need changing. He said the guides only wear if the valves are set up wrong and they are putting a side torque on the guide.