Damn Oil!!

[Y33TREKker]

If it's blowby though, isn't the only way that oil could get back up into the intake is if it went through the PCV system? No excess pressure at the oil filler cap would seem to indicate that it's not blowby, although if it was only checked at idle the higher rpm condition described wouldn't have been addressed.

For whatever reason, the PCV systems on individual VX's seem to just be hit or miss as to whether they function correctly. A simple breather filter to replace the PCV valve eliminates even the chance of what's being described as happening though.

If a VX suffers from oil usage because of a problem with the piston rings, oil usage is going to occur anyway, regardless of whether a PCV system is even in place.

[PK]

Yes, a stickey ring. At idle the ring conforms just fine to the cylinder walls. At higher rpm the ring cannot move in the lands fast enough to seal against compression, resulting in blowby, hence your mess...You could try a flushing agent such as Sea Foam in your crankcase and hope for the best, otherwise a rebuild may be in your future. Sorry.

Scott, you are correct. A sticking ring might need a higher load than idle for it to play up. Possibly even more load than just revving the engine while stationary, so it is hard to test that one.
The Sea Foam treatment could work.

If it's blowby though, isn't the only way that oil could get back up into the intake is if it went through the PCV system? No excess pressure at the oil filler cap would seem to indicate that it's not blowby, although if it was only checked at idle the higher rpm condition described wouldn't have been addressed.

For whatever reason, the PCV systems on individual VX's seem to just be hit or miss as to whether they function correctly. A simple breather filter to replace the PCV valve eliminates even the chance of what's being described as happening though.

If a VX suffers from oil usage because of a problem with the piston rings, oil usage is going to occur anyway, regardless of whether a PCV system is even in place.

Trekky, IIRC there are 3 rings on our pistons.
The top ring seals compression in the cylinders.
The bottom ring controls oil on the cylinder walls.
The middle ring is multipurpose - it does a bit of each.

So, it is possible to have excessive blowby without being an oil burner, and vice-versa.

PK

[Ldub]

Trekky, IIRC there are 3 rings on our pistons.
The top ring seals compression in the cylinders.
The bottom ring controls oil on the cylinder walls.
The middle ring is multipurpose - it does a bit of each.

So, it is possible to have excessive blowby without being an oil burner, and vice-versa.

PK

X a factor of 2...

I've gutted my PCV system, & it now flows freely into a catch can, which is vented into the air box, with zero reduction in oil consumption.

[Ebenezr]

X a factor of 2...

I've gutted my PCV system, & it now flows freely into a catch can, which is vented into the air box, with zero reduction in oil consumption.

This is an interesting idea Dub. I thoughtof running my pcv down into a canning jar with some kind of filter and then back out again to the intake. I dea being the oil would be filtered out and fill the jar.

[Ldub]

This is an interesting idea Dub. I thoughtof running my pcv down into a canning jar with some kind of filter and then back out again to the intake. I dea being the oil would be filtered out and fill the jar.

That's what I thought too...

The strange thing is, there is plenty of evidence that there is oil being forced from the valve covers. There is always an accumulation inside the air filter box.
But I've never seen any accumulation in the catch can....

It's either travelling so fast as a mist, that it goes right through the can, or something came loose inside the can, or I need to add more steel wool as a baffle.

Gonna have to look into it come spring...

Lastly...find yourself a nice aluminium container...I think that a glass jar would be kinda sketchy under the hood.

[Y33TREKker]

Scott, you are correct. A sticking ring might need a higher load than idle for it to play up. Possibly even more load than just revving the engine while stationary, so it is hard to test that one.
The Sea Foam treatment could work.



Trekky, IIRC there are 3 rings on our pistons.
The top ring seals compression in the cylinders.
The bottom ring controls oil on the cylinder walls.
The middle ring is multipurpose - it does a bit of each.

So, it is possible to have excessive blowby without being an oil burner, and vice-versa.

PK

Trekky?

Anyway...

I was just going by your original post, and not the additional things you've now brought up. If you guys want to have yet another discussion regarding the various trains of thought regarding oil consumption in VX's, have at it.

But as I said, even if there is blowby, it still has to go through the PCV system for oil to get to the intake, which is what we're trying to figure out for p_justin.

[Scott Larson]

Trekky?

Anyway...

I was just going by your original post, and not the additional things you've now brought up. If you guys want to have yet another discussion regarding the various trains of thought regarding oil consumption in VX's, have at it.

But as I said, even if there is blowby, it still has to go through the PCV system for oil to get to the intake, which is what we're trying to figure out for p_justin.

Further discussion? Don't mind if I do, thanks!

Positive Crankcase Ventilation is exactly that, it allows for the ever-changing volume of air in the crankcase to be expelled and subequently replaced as the volume changes due to the reciprocating pistons in their bores. If you introduce an oil mist into that atmosphere, either due to oil being blown by the pistons rings or too much oil in the sump being contacted by the crank journals, that oil will find it's way out of the pcv system along with the air. A small amount of oil mist is normal, it is when it becomes excessive that you have the problem described...ultimately, it is the function of the pcv valve to regulate or control the volume of air entering or leaving the crankcase, not to separate oil from that air. Provided all internal baffles are in place to impede the flow of normal oil mist, a catch can is not required.

Hope that helps!

[Y33TREKker]

Positive Crankcase Ventilation is exactly that...

When it's working properly of course. Given all the related problems seen to date on this board though, it's still debatable whether the design of the PCV system on VX's actually works the way a PCV system is supposed to work.

[VX KAT]

Yes, a stickey ring. At idle the ring conforms just fine to the cylinder walls. At higher rpm the ring cannot move in the lands fast enough to seal against compression, resulting in blowby, hence your mess...You could try a flushing agent such as Sea Foam in your crankcase and hope for the best, otherwise a rebuild may be in your future. Sorry.

So, it is possible to have excessive blowby without being an oil burner, and vice-versa.

PK

If it's blowby though, isn't the only way that oil could get back up into the intake is if it went through the PCV system? No excess pressure at the oil filler cap would seem to indicate that it's not blowby, although if it was only checked at idle the higher rpm condition described wouldn't have been addressed.

For whatever reason, the PCV systems on individual VX's seem to just be hit or miss as to whether they function correctly. A simple breather filter to replace the PCV valve eliminates even the chance of what's being described as happening though.

If a VX suffers from oil usage because of a problem with the piston rings, oil usage is going to occur anyway, regardless of whether a PCV system is even in place.

Further discussion? Don't mind if I do, thanks!

Positive Crankcase Ventilation is exactly that, it allows for the ever-changing volume of air in the crankcase to be expelled and subequently replaced as the volume changes due to the reciprocating pistons in their bores. If you introduce an oil mist into that atmosphere, either due to oil being blown by the pistons rings or too much oil in the sump being contacted by the crank journals, that oil will find it's way out of the pcv system along with the air. A small amount of oil mist is normal, it is when it becomes excessive that you have the problem described...ultimately, it is the function of the pcv valve to regulate or control the volume of air entering or leaving the crankcase, not to separate oil from that air. Provided all internal baffles are in place to impede the flow of normal oil mist, a catch can is not required.

Hope that helps!

Just curious how this all works.....So when you say "blowby", does that mean the oil or oil mist actually gets PAST the piston ring when it's going up/down, but not fast enough, and is pushed up and out of the cylinder through the PCV?
Why wouldn't that oil/mist combust within the cylinder and result in white smoke?


PK, explain this again.....
"So, it is possible to have excessive blowby without being an oil burner, and vice-versa."


Overall, I'm still amazed at how important that dang $3 part is.....

[PK]

PK, explain this again.....
"So, it is possible to have excessive blowby without being an oil burner, and vice-versa."

Well, this is my understanding of how piston rings work, but I am not specifically a trained mechanic.

The top ring is solid in cross section, and slides hard against the cylinder wall. It has the primary function of keeping the combustion gasses and compression, in the combustion chamber. Excessive blowby occurs if this ring, or the cylinder walls, are worn or scratched. Also, if the ring groove in the piston is worn, the ring can stick so that it is not hard against the cylinder wall.

The bottom ring has special contours in cross section. Its prime function is to take most of the oil (not all) off of the cylinder walls. This oil is thrown up by splashing of the crankshaft etc as it rotates, and also from the oily mist that is always in the sump when an engine is operating. This ring actually guides some of the oil back into the ring groove and back to sump through drain holes in the piston skirt. That is why there has been some talk about the piston drain holes being responsible for the VX burning oil. If the drain holes clog up, or the ring wears or sticks, you have an oil burner.

The middle ring helps restrict any blowby that gets past the top ring, and any oil that gets past the bottom ring. It also covers the "gap" area in the top and bottom rings. But it is not 100% efficient in either role, so if the other rings are worn, some of the excess still gets past.

Depending on what is worn and how much, you can have an oil burner that still has good compression and no blowby. You can also have excessive blowby and not be a large consumer of oil.
However, the normal would be for relatively even wear, and you have both blowby and oil burning.

Note that the rings are never 100% efficient.
If the oil rings took every little bit of oil off the cylinder walls, the top ring would wear very quickly, so a small film of oil is always there to lubricate the top ring.
This is what is considered "normal" oil consumption, and different manufacturers will rate their engines differently.


Now, you guys have to decide if I have blinded you with science, or baffled you with bull scat??

PK

[Monstertrucker]

Positive Crankcase Ventilation is exactly that, it allows for the ever-changing volume of air in the crankcase to be expelled and subequently replaced as the volume changes due to the reciprocating pistons in their bores.

Not quite; it's thermal and gaseous expansion that we're concerned with since the crankcase pressure doesn't change due to mechanical movement; piston ring and stem seal blowby notwithstanding, of course.

As a pair of pistons go up, a pair go down so it's a static volume in that regard.

[Scott Larson]

Not quite; it's thermal and gaseous expansion that we're concerned with since the crankcase pressure doesn't change due to mechanical movement; piston ring and stem seal blowby notwithstanding, of course.

As a pair of pistons go up, a pair go down so it's a static volume in that regard.

Staggered timing negates your theory...no difference between one cylinder or sixteen, sorry!