Rockerbox breathers

[TomoHawk]

Is there anything else than the Spectre Performance cone filters that you can use on the rocker box?   The biggest one in the AP stores only has a 10 or 13mm neck, and the tube on the top of the rocker box has an 18mm (3/4 inch) tube.  I thought a small diameter inline filter would be better than a 2 inch cone, and I don't like piping the oil blow-by into the intake manifold  Check the lawn mower or cycle shop maybe?

 

thxZ

[black gold man]

Unless you got carbs  you should have no breather it is a big vacuum leak. 

[TomoHawk]

plugging the tube makes no difference.

[black gold man]

If you close it up and makes no difference then you have a leak somewhere else.

[TomoHawk]

That's unlikely, as the engine was rebuilt, but it is conceivable.  The throttle is a good place for a leak.

 

Still, the vent tube is unsightly, and a small filter would give it a look of purpose.  Even a short tube with an inline filter would look better.

Edited August 10, 2015 by TomoHawk

[Chickenman]

K&N makes breather filters  that have a 3/4 rubber neck. But, you should not be using a vented filter straight off the Valve Cover on Fuel injected motors.

 

As noted previously, FI motors draw the vent air ( for the PCV system ) from behind the AFM, so it is metered air and the ECU can compensate. If you use an open port or open filter on the Valve cover for PCV venting, you will create a lean condition as air is being sucked in from Atmo, drawn thru PCV system system and into Intake manifold without being measured by the AFM. 

 

Best way may be to add an Oil catch tank or oil separator. That will prevent oil vapors from being sucked into the Intake manifold. If fuel injected, make sure you use a closed Catch can with no vent on the top.

 

Edit: Carbed cars are calibrated with the Valve cover vent open to atmosphere... opposite to EFI. 

Edited August 10, 2015 by Chickenman

[TomoHawk]

Would you include a PCV check valve?  I suppose they make it in 3/4 inch.  I'm still wondering how all that oil got through the hose and into the throttle & intake manifold.  The old breather was soaked with  oil.  There must be a bit of oil vapor sneaking through.

[Chickenman]

Since the normal air flow for the PCV valve is drawing into the Rocker Box  thru the PCV valve and then into the Intake manifold, I would suspect that an abnormal amount of oil in the vent hoses would indicate a malfunction in either the PCV valve itself or a split PCV hose. The PCV hoses love to split on the where it's hard to see, from all the heat from the exhaust manifold.

 

If the PCV system is not working correctly, then you build Positive pressure in the cranckacse and it will push oil out the Rocker Box vent tube.

 

I replaced the stock Nissan PCV hose with reinforced high temperature silicon hose and no more worries about split rubber PCV hoses. 

[Chickenman]

One other thought. Chcek the inside of the Rocker Box. The factory system has a very well designed Oil Baffle plate the covers the vent hole. Some aftermarket companies remove these baffle plate when they are Media blasting the Valve Cover for polishing or Powder coating. If they don't replace the Baffle ( screws are epoxied in from factory ) you can get oil spray being flung out of the vent tube at WOT.

 

At WOT, PCV airflow is reversed ( no vacuum )  and blow-by gases will flow out of the vent tube. Not a big deal as engine is designed for this... but if VC baffle plate is missing then you can get a large amount of oil being pushed through the vent tube.

 

Edit: I had that exact problem ( no baffle plate ) on my 280Z. PO had installed a very nicely Chrome plated VC. But plater's media blasted it and removed the inside oil baffle and never replaced it. Large amount of oil collecting in vent tube and hoses. Got a donor VC, removed the epoxy from screws( not that difficult ) and removed oil baffle plate. Installed the baffle plate in my Chrome valve cover and no more oil in vent tube. Be sure to epoxy or use Red Loctite on screws.

Edited August 10, 2015 by Chickenman

[TomoHawk]

That's probably why the breather was oil-soaked (from the WOT oil-spray.) I will let the plater know about the baffle when I get the thing plated. But for now, I'll stuff a plug in the tube, and  maybe use the old breather for show.

[Chickenman]

That's probably why the breather was oil-soaked (from the WOT oil-spray.) I will let the plater know about the baffle when I get the thing plated. But for now, I'll stuff a plug in the tube, and  maybe use the old breather for show.

 

I wouldn't stuff a plug in that tube ( VC vent tube ). The  PCV system needs to draw air through the valve cover to equalize flow. Plugging the VC vent tube will cause other problems.

 

Dig a bit deeper and find out what's going on. It's a very simple system. At the minimum, temporarily put a K&N style breather filter on it. Not ideal for EFI, but it's better than plugging the vent or leaving it open with no filter.

Edited August 10, 2015 by Chickenman

[Chickenman]

Delete.. double post.

Edited August 10, 2015 by Chickenman