Valve Stem Seals

The question has been raised as to whether valve stem seals are necessary on only the intakes or if they are needed on the exhausts, too.

The response from MarkLangford was that they are unnecessary on either intake or exhaust valves beyond the and that WW shared this view. His reason was that aircraft engines don't experience the high vacuum situation one gets in a car going downhill with the throttle shut, so it's not a problem in our usage. He left them off his first Corvair engine because of experience he had had with a VW aircraft conversion where they just melted off and ended up in the sump at the first oil change.

RadDavis posted that valve stem seals on Corvair cars help keep oil from oozing into the intake and exhaust ports when the car is parked on an incline and oil pools in the downhill rocker box. Oil in the exhaust port causes a light blue puff at startup from oil down the exhaust valve stems . In extreme cases, enough oil down the intake valve stems can cause misfire due to fouled plugs on startup. There is also the concern that car engine spends a lot of time at idle and light loads where there is a high intake manifold vacuum, and some wear on the intake valve stems can result in a lot of oil being pulled down the intake valve stems and result in heavy restrictive carbon deposits on intake valve heads . A tight clearance between valve and guide is needed and lubrication helps prevent it from becoming loose, and the ValveStemSeal restricts oil flow into this space. It's a particular concern on the exhaust valves, which run much hotter and don't have the consistent strong difference in pressure to pull oil down the valve stem and keep them lubricated and cooled. For this reason he argues that there is no reason to use exhaust stem seals ever - all they prevent is a momentary puff of blue smoke on startup. Rad Davis said that this was why he called the Corvair engine the 'blue smoke six' and that Corvair pilots should accept this part of the engine's character and be grateful it's not a radial or a two-stroke.

Related terms:

IntakePort , ExhaustPort , ExhaustValveStem , IntakeValveHead