Valve Stem Seals

[BlindAmbition]

For a 6.9 motor, what are the best valve stem seals to use? I see threads saying to just put intake seals on the exhaust, I see others saying that ruins valves and to use the umbrella style. I've searched threads on here and FTE, and found more differing opinions than I have toes regarding which style to use. Any input would be appreciated.

https://www.rockauto.com/en/catalog...v8+diesel,1124020,engine,valve+stem+seal,5800 - Here is the rockauto listing for my engine.

 

[XOLATEM]

I would not use polyacrylic seals...lower threshold of damage from heat...Viton would be better...I would have to look up the difference between viton and silicone to make a judgement call on which is going to last longer...

As far as whether to use them at all...remember that you create a vacuum on deceleration and that would tend to pull oil from around the valve stem into the cylinder...bad for a spark ignition engine and probably not noticed in a compression ignition engine...except for oil consumption...which would tend to foul a catalytic convertor...not an issue for older diesels...

What would I do in your situation...? Depends on how much clearance you have at the valve-to-valve guide interface...

The exhaust valve sees only heat...it does not get any cooling air from the intake system...any cooling it can get would help...especially if the clearance is snug...it is a judgment call that I would consult with an experienced engine builder about...

On the intake..? same deal....consult with the guy that is building your heads...because he knows how much oil clearance you have and how much is allowable...

Pretty much the only real advice I can contribute is to steer clear of polyacrylic seals...they were responsible for a lot of burned up clutches in auto transmissions...back in the day...

 

[BlindAmbition]

Viton seems like the best choice for longevity. I am worried about starving the oil on the exhaust valves as I've read about it happening when going to a positive-ring style seal.

I'm the guy "building" the heads, they are still attached to the engine in the truck. I'm putting Comp Cam springs in and the umbrella type seals don't fit well.

 

[Noiseydiesel]

"starving the oil on the exhaust valves as I've read about it happening when going to a positive-ring style seal." is a viable concern.
What came off? Anything?

 

[Kevin 007]

Viton seems like the best choice for longevity. I am worried about starving the oil on the exhaust valves as I've read about it happening when going to a positive-ring style seal.

I'm the guy "building" the heads, they are still attached to the engine in the truck. I'm putting Comp Cam springs in and the umbrella type seals don't fit well.

Following. Did you come up with anything. Im a fan of the umbrella type but as you say, they don't fit well under the Comp 910's. I don't want anything too positive on the exhaust side.

 

[ihc1470]

As far as whether to use them at all...remember that you create a vacuum on deceleration and that would tend to pull oil from around the valve stem into the cylinder...bad for a spark ignition engine and probably not noticed in a compression ignition engine...except for oil consumption...which would tend to foul a catalytic convertor...not an issue for older diesels...

Can you explain how a diesel engine can build vacuum since there is no throttle plate in the intake system.

 

[DaveBen]

Today's diesels have a vacuum pump that is electrically or belt driven. The engine it self can not create a vacuum.

 

[BlindAmbition]

I installed positive seals on all of the valves, posted on the IDI FB group with the same question, Justin at IDI Performance said it's all he runs so I went with it. Still working on truck so I cannot vouch for if they work, so take whatever I say with a grain of salt.

 

[hacked89]

You can run no valve seals on the exhaust valves if you choose. It will just smoke on initial startup.

 

[XOLATEM]

Can you explain how a diesel engine can build vacuum since there is no throttle plate in the intake system.

The engine it self can not create a vacuum.

GUYS...how does the air get into the cylinders...??

Every time an intake valve is open and an exhaust valve is closed and the piston retreats from the head surface the engine is pulling a vacuum...

It is just not as pronounced as a vacuum would be in a healthy gas engine that has a throttle valve...

You two are confusing MANIFOLD vacuum with negative cylinder pressure...which essentially is the same thing as a 'vacuum'...

Isn't it...?

Now...I could be wrong here...and if I am...I am sure you all would speak up and once I 'see' things your 'way' I will admit it...

But...I was towing a 10K trailer pretty much fully loaded and coasting down a hill to the point that 'things' were getting kinda fishtaily...and had to drag the brakes to keep it under control...

But it sure 'felt' like the engine was capable of pulling top-end oil through loose valve stems...if they were loose...which...I don't know...

and... it sure felt like I had some engine braking helping things...which-to me- would have indicated that the engine was pulling a vacuum...more so that if I was just cruising on level road.

" probably not noticed in a compression ignition engine...except for oil consumption..."

Didn't I address your concern already with the above quote from the post of mine that you quoted...?

You can run no valve seals on the exhaust valves if you choose. It will just smoke on initial startup.

I believe his evaluation and belief...so...tell me how the oil got past the valve and into the cylinder to be burned...?

Was it just capillary action...?

Edit...lets do a 'vacuum test'...how about it...

Lets back off the adjustment on all of the valves...let them all be closed against valvespring pressure...and then break loose the injectors at the lines so no fuel will be forced into the cylinders...

and then hit the key and see if you can get the engine to crank over...???

No vacuum...? out of your engine...?

What do you think would happen...?

 

[ihc1470]

GUYS...how does the air get into the cylinders...??

Every time an intake valve is open and an exhaust valve is closed and the piston retreats from the head surface the engine is pulling a vacuum...

It is just not as pronounced as a vacuum would be in a healthy gas engine that has a throttle valve...

You two are confusing MANIFOLD vacuum with negative cylinder pressure...which essentially is the same thing as a 'vacuum'...

Isn't it...?

Now...I could be wrong here...and if I am...I am sure you all would speak up and once I 'see' things your 'way' I will admit it...

But...I was towing a 10K trailer pretty much fully loaded and coasting down a hill to the point that 'things' were getting kinda fishtaily...and had to drag the brakes to keep it under control...

But it sure 'felt' like the engine was capable of pulling top-end oil through loose valve stems...if they were loose...which...I don't know...

and... it sure felt like I had some engine braking helping things...which-to me- would have indicated that the engine was pulling a vacuum...more so that if I was just cruising on level road.

" probably not noticed in a compression ignition engine...except for oil consumption..."

Didn't I address your concern already with the above quote from the post of mine that you quoted...?


I believe his evaluation and belief...so...tell me how the oil got past the valve and into the cylinder to be burned...?

Was it just capillary action...?

Edit...lets do a 'vacuum test'...how about it...

Lets back off the adjustment on all of the valves...let them all be closed against valvespring pressure...and then break loose the injectors at the lines so no fuel will be forced into the cylinders...

and then hit the key and see if you can get the engine to crank over...???

No vacuum...? out of your engine...?

What do you think would happen...?

Easy way to prove it to yourself is install a vacuum gauge on the intake manifold of a diesel and see what you read. Vacuum is created when a there is a restriction in the intake so less air can move into the cylinder when the piston is moving down.

Put a vacuum gauge on a gas engine and you will see the highest vacuum at an idle. Open the throttle and the vacuum drops off as there is less restriction to the air flow.

There is no throttle plate used on a diesel. Some diesel engines such as a Detroit Diesel have an emergency shut off plate in the intake to close off all air in case of a run away, but normally that is open.

You are correct to a point that there is a very slight degree of vacuum as the air cleaner will create a very slight restriction and as it gets dirty that restriction will increase.

The original question was seals on the exhaust valves. As far as pulling oil past an exhaust valve with vacuum how can that even happen? Think about it, when the piston is on the intake cycle moving down the exhaust valve is closed so the stem should not even be exposed to vacuum. When the exhaust valve is open the piston is on an up stroke expelling the cylinder at that point in time the exhaust valve is under pressure.

 

[XOLATEM]

Explained: Why Diesel engines need a throttle body & throttle plate

Explained: Why Diesel engines need a throttle body & throttle plate

www.team-bhp.com

Your post is very well written and explains the basic differences on older engines in a way that would give a student a good picture of the basics...

But...what you are explaining in detail is air movement up to the intake valve and not in the cylinder... and I am referring to air movement after the intake valve on a NA older diesel.

I am not saying that there is any significant vacuum in the intake manifold other than what you pointed out from air filter restriction.

Thanks for the detail about Detroit engines...I did not know that and it was another thing to investigate when I feel inspired to look into it and learn about them.

On my point...

Since the swept volume of a diesel cylinder is...lets say 'X'...when the piston is at the bottom of its stroke...and the speed of the piston is 'X' when it is moving in the downward direction...and the intake valve opening is many times smaller than the swept volume of the whole cylinder...I am talking NA here...not forced induction...then the only way the cylinder can fill is by the piston creating a vacuum in the cylinder.

I believe you are talking about MANIFOLD vacuum...and I am talking about the dynamics of CYLINDER filling...

Which...by the way...there is an overlap period in the cycle where the intake and exhaust valve are open at the same time...although very short in this instance...but I would bet that would explain at least some portion of the oil getting past the exhaust valve past 'loose' valve guides and into the cylinder to create the...

It will just smoke on initial startup.

I believe you are basing your rationale of the unlikelihood of oil being drawn into the cylinders by vacuum from thinking that the intake and exhaust events are seperated to the point that they do not coincide at any given point in the cycle...we would have to take a diesel cam and set up a pair of dial indicators on the lobes and turn the cam one turn and observe the events...

I would be interested in seeing that...and as soon as I get my hands on a cam...I am going to try it...better yet...I need a block, cam, lifters and cam gear...then I will know for myself if any overlap occurs...

Or...we could ask one of the guys that builds the engines or grinds the cams...

The original question was seals on the exhaust valves. As far as pulling oil past an exhaust valve with vacuum how can that even happen? Think about it, when the piston is on the intake cycle moving down the exhaust valve is closed so the stem should not even be exposed to vacuum. When the exhaust valve is open the piston is on an up stroke expelling the cylinder at that point in time the exhaust valve is under pressure.

You have a good question and a good point here...

I want to know, too...and then we can put this to bed and move on...

This reminds me of when Morpheus is trying to introduce Neo to the concept of everything he believed to be true was a lie and created to keep him in a tub...plugged in and generating energy for the Machines...

This also is reminding me of something my Dad told me about him having an argument with a science teacher...he said that...when you draw water through a straw out of a glass...the water moved through the straw by creating a partial vacuum...the science teacher said that the water moved by atmospheric pressure.

Sounds like two ways to explain the same concept...

Waiting to see what come next...this is thought-provoking...

 

[Booyah45828]

You can run no valve seals on the exhaust valves if you choose. It will just smoke on initial startup.

That's what I've contemplated doing. So long as the guide-valve clearance is correct, it will be minimal. These engines seem to chew through guides as is, not sure if you could over lube them. This whole topic has me wondering why the idi's do go through guides as bad as they do. Are the rockers sideloading the valves in some way? Would roller rockers fix this? Or is the solution bronze guides and no seals?

We ran no seals on the race engines. I can say right now the amount of smoke produced at startup was minimal. Unless the engine design submerges the springs in oil, the only time I really see oil consumption past guides is because of loose guides as much as it is failed seals.

 

[Kevin 007]

And many of us, including myself; see less guide wear in 6.9's. Only thing that makes sense is the looser/non existent valve seals.

 

[Booyah45828]

IMO if you're turbocharged, at no time will there ever be a vacuum(pressure below atmosphere) in the engine. Even if you weren't the tiny amount, if any, of vacuum created would be very difficult to measure. Like inches of water small. Not enough to pull oil past a correctly sized guide.