logskidder

Compression and boost will go past worn or defective valve seals......common problem on the B and C series.

thek0rn

well that will be the next step, i will let you guys know what i find. thanks alot for all your help

thumper549

OK I am game here Please explain how 20 0r 30 lbs of boost will be held back by a valve stem seal ??
Where would it go ?
If a umbrella seal could do that....
Now don't get all in a up roar, just curios ....truly
Compression is inside the combustion chamber, No way will a stem seal stem that ....LOL ( couldn't resist)
A worn guide / valve stem seal will let in oil
A stem seal never sees compression.......unless there is something awfully wrong.
Boost is in the intake port...would have to force its way up past the guide would it not ?
There is not a lot of over lap in the valve / cam timing (being a turbo it cant )
Please read this like we are having coffee together. Just wondering how this works, your turn

logskidder

Its the turbocharger for the most part. When boost makes it way past worn valve seals, the crankcase receives the pressure.....pressure that will force the oil mist out the breather. Trust me when I say I have pulled my hair out over this problem years back. Jeff Mumau 724 354 3994 from Mumau Diesel and the local Cummins Rep helped me figure it out. Im not saying this is the problem, however its something to look for.

thumper549

OK , some one is wa wr wro wrong here...The turbo compresses air say 20 lbs full boost stock eng.
In a perfect world with no leaks from Turbo to intercooler to manifold to inside the intake ports in the head you will see the boost pressure (keep in mind the turbo is capable of much more.)
So lets say the seals are wore out ?
There is 1.5 thou for the boost to climb up the the valve stem and guide...20 to 30 lbs of preasure...the umbrella seal as I see it will not stop this ..for one thing they are designed to "stop" from the top direction.
So if boost is going up the stem...the guides would have to be wobbling around pretty bad..doubt the valves would be landing on their "face" surface every time either..

logskidder

If you have a service manual....check it out. Or call Jeff Mumau (real nice guy) and he will explain the dynamics of this issue. He is an authorized Cummins dealer. Also the seals are designed to "stop" from both directions if you have one handy check it out and you will see why I say that.......turbo boost is the main reason these seals are built so heavy.

Busboy

Not to take sides here but I have to agree that boost pressure is likely causing the problem and there aren't many places that it comes in contact with the case. The intake valve guides and seals is really the only place. With worn guides and/or bad seals all it needs is boost pressure above crank case pressure and you will have flow into the case. You won't see this on a normally aspirated gas engine as there is vacuum on the intake.

logskidder

No taking sides...it is what it is. Years back this topic was not in the B series service manual......Now I think its #2 or #3 in the troubleshooting steps for blowby.

nitrousn

You can throw the valve seals away and not create any more blowby. The guides and valve stems can be worn out and no seals and you wont create any more blow by. Blow by is a direct result of piston ring and possible piston failure. Compression is by passing rings/pistons into the crank case creating the blow by.

Valve stem seals and worn guides will allow oil into the combustion chamber but will not create blow by.

logskidder

Ever watch the breather tube on a high rpm, high psi pull truck?? I guess they all have worn out rings. The problem here is...The guy has good compression with high crankcase pressure........check valves seals. Or should we tell him to just replace the engine??

logskidder

Also.....why are the valve seals in the Cummins troubleshooting steps for high crankcase pressure if it cant happen

logskidder

Had to hit 500

thumper549

OK , So and So says this and So and So says the opposite.
Someone go change out the valve stem seals and see What we get...I would love to know the results.
And I know no one is taking sides..we are having a discussion, all is good !!

thek0rn

while im in there to do a leakdown test, ill check the seals. say a seal did break/crack or is leaking, wouldnt i get some oil running down the stem into the combustion chamber causing a bit of blue smoke?? or could it leak enough pressure past but not be bad enough to let an excessive amount of oil past??

Lil Dog

I have seen valve stem seals cause the same problem on a Cat G379 engine. Borescoped the engine with no liner damage, leak down test showed good seal and compression was good. But the engine would puke oil out of the valve covers and the crankcase pressure was almost 1 psi.. The valve seals were the culprit.

It is not a shot in the dark. If you think about a 24V, thats alot of valve stems on the intake side to hold back.