Bad Valve Seals..?

[Girvin]

So after months of having excessive crankcase pressure and leaky valve cover gaskets I found my problem........or atleast figured out most of it.

The symptoms Im seeing other than the excessive pressure is slow spool and loss of power under boost. I did a boost leak test and found that while pressurizing the intake the valve cover and crankcase were pressurizing as well, I had to plug the valve cover vents to get any boost out of the test.

Thinking that I had bad rings or a headgasket problem I started with a compression test..............the compression test turned out very good with only a max 2psi between all cylinders and was in spec(Im 17,000kms on a rebuild). So the apparent problem should be a valve stem seal, correct? Though Im not buring any oil......or atleast enough to see in the exhuast.

Is it possible that a valve stem seal is leaking only under boost? I would like to get away with just replacing a seal than pulling the head to do the guide as well. Ive been having this problem since the rebuild, its getting progressively worse, could it be the one of the valve seals didnt seal on the initial rebuild?

Tomorrow Im going to do an intake leak test with the valve cover off ..........to see exactly where the leak is coming from.........it should obviously be on the intake valve side..

Any help would be greatly appreciated

 

[turboholic]

Is it possible that a valve stem seal is leaking only under boost? I would like to get away with just replacing a seal than pulling the head to do the guide as well.

-Valve stem seal is different from valve seat, the prior keep oil from going into the combustion chamber through the valve, has nothing to do with compression, the latter keep tight seal between the valve and the head, has every thing to do with compression.

 

[Girvin]

I understand what your saying.........My compression and leakdown tests turned out fine, so there is no problem in the combustion chamber. So there seems to be some confusion here. I just finished an intake leak test but with my valve cover off..

The test made it very clear that one of my valve seals is fubar'd. When I pressurize the intake, via compressor on a coupler attached to the compressor housing of the turbo, there is a LOUD leak on the #2 cylinder left valve. It bubbles any oil that is around the stem. Which in turn is basically pressurizing my valve cover on a 1:1 ratio with intake pressure(boost). Im going to have a shot at replacing the seals tomorrow.

 

[Mike000]

You sure the leak is not coming from the turbo? The bubbling oil noise you hear is normal.

 

[Girvin]

just finished installing new valve seals.........used mitsu ones this time around..........problem fixOrd.

 

[pinknuggit]

The only way you can get pressure through the valve stem seal is if your valve guide is out of spec. The guide can be worn and can cause extra clearance between the valve stem itself and the inside of the guide.
Did you have your head rebuilt when you rebuilt the whole motor? I'd look into that because even with no seals on the valve stem, you should not get any pressure through the guide/valve stem clearance.

 

[Girvin]

yes the head was rebuilt when the bottom end was done......new valves, guides and seals 12,000kms ago.

 

[Defiant]

Delighted you got it fixed. I still have no idea what you had wrong, nor what you corrected with valve stem seals.

In the interest of future clarity, closed.