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Hi,
I’m a little late spotting this post about intake valve seals.
I was thinking that an upper head gasket set only comes with four seals, for a two valve four banger?
I agree that they are not warranted to be on exhaust valves.
The reason they are used on intake stem guides is because of vacuum around the intake valve stem.
This is especially true when the throttle valve is suddenly closed up or even partially closed down rather quickly. The engine spins on while Driving in town and up and down hills.
This will cause the vacuum to continue on into the combustion chamber.
This also pulls oil up past the piston rings when the intake valve opens. Cars can smoke more when shifting as we all know.
Oil burning is contributed more to the piston rings and then it’s valve guides.
Also comes down to the amounts of circumferences!
The pistons are always working four times more to keep the oil down, where the intake valves are only one fourth of those cycle numbers.
I have often thought that the leaning of the cylinders over to one side slightly and having the intakes on the upper side, would help reduce oil exposure, besides, giving up more room for access to the intakes hidden components!
A vacuum cannot happen to the exhaust valves as the intake is never open to influence the exhaust valves because, they, the exhaust valves, open only on the other side of the combustion cycle.
The exhaust manifold causes more of a chance of the exhaust valves ports to be slightly pressurized. This is due to other cylinders firing and back pressure that builds up in the pipes and mufflers.
It stands to reason, with the reasoning above that the likelihood of the exhaust valves being hotter the seal would not last nearly as long.
The intake valves run cooler due to incoming air and fuel mixture flowing by.
Like you said, you don’t want a valve to stick due to lack of lubrication and have it start leaking. This is when the burning a seat ring or valve tulip.
This brings on a “True Heartache” with the way we love our Volvos.
Happy New Year to all!
Just working on being more of an vintage classic, than a has been!
(:-)
Phil
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