Oil from block vent confirmed.

[cygnusx1]

Tonight, I pulled off the head to replace the head gasket that I had installed incorrectly. It was a record. I had the head off in two hours flat by myself. Anyhow, the PCV hose that delivers blow-by from the block vent was very oily on the outside. On the inside it was even worse. The intake manifold, once removed, was dripping oil out of the runners and you could feel the oil inside the intake ports. The intercooler pipes were dry as a desert, so the only way the oil was getting into the intake manifold is the PCV. Finally I have positively confirmed that I am not burning all that oil from my valve guides and rings. Now what to do.....stay tuned.

[TimZ]

Tonight, I pulled off the head to replace the head gasket that I had installed incorrectly. It was a record. I had the head off in two hours flat by myself. Anyhow, the PCV hose that delivers blow-by from the block vent was very oily on the outside. On the inside it was even worse. The intake manifold, once removed, was dripping oil out of the runners and you could feel the oil inside the intake ports. The intercooler pipes were dry as a desert, so the only way the oil was getting into the intake manifold is the PCV. Finally I have positively confirmed that I am not burning all that oil from my valve guides and rings. Now what to do.....stay tuned.

 

I hate to say it, but that's usually an indicator of excessive blow-by, and that often doesn't end well...

 

Maybe not, though. There is a sort of "pocket" in the block where the crank vent is pressed into, and in that pocket is supposed to reside a flame arrestor - it looks like a piece of screen, folded accordion-style. Then, there is a small sheet metal piece that bolts in over the flame arrestor to hold it in place. If you don't have this stuff installed, then you can get quite a bit of oil splash into the crank vent.

 

Do you see oil trying to squish out of other points, like the oil filler cap, or is it just at the crank vent?

 

Another thing to look at might be any plumbing that would allow boost pressure form the intake manifold to get into the crankcase.

 

Also, when you say the previous head gasket was installed incorrectly, how so? Could that have contributed?

[cygnusx1]

Thanks, Tim!

 

I know it sounds bad but if you saw how clean this motor looks inside the bores and the fact that compression tests are excellent, and the head has just been rebuilt, you would not point to excessive blow by.

 

I have the valve cover vented to atmoshpere which makes it "easy" for the intake vacuum to suck clean air into the valve cover and oil-mist out of the crank case vent.

 

The history of oil getting sucked into the intake through the PCV valve began when I eliminated the AFM and the hose from the fresh air intake pipe to the valve cover. What I think happens now is that since there is ZERO vacuum on the valve cover side, the PCV valve has too much authority; if that makes sense to you.

 

In order for turbo clearance, I also had to mount the PCV valve at about 45 degrees instead of vertical. This, in effect, changed the spring rate of the check function, allowing MORE PCV to happen in the low to mid vacuum states.

 

The combination of things results in a lot more flow from the block vent. There are no signs of oil at the valve cover vent at all. A clear indication that there is heavy flow in the downward direction and out the block vent. As far as the oil mist collector in the block, I have no idea of its condition.

 

What I need to do is to make sure the crank case is mostly always under a vacuum condition, yet still maintain a (controlled) flow direction for case ventilation.

 

I have some thoughts mulling around.

1) Fix the angle of the PCV valve.

2) Use an exhaust scavenge vacuum pipe with a catch can from the block vent.

3) Put a fresh air restrictor (adjustable flow valve) on the valve cover vent to control flow through the crankcase during high intake vacuum.

4) Hook the valve cover vent back to the turbo inlet pipe to create "counter vacuum" to reduce crank case flow.

5) Rig a sealed catch can between the block vent and PCV in combo with point 3)

 

I think all of them have their + and -, and most can be combined with eachother so I will need to experiment. Of course I can just re-create what Nissan did from the factory and leave it at that.

 

Currently, it only smokes visibly when you coast downhill with a DEAD COLD engine for the first few minutes of driving. This is because all of the oil mist from the previous drive has settled into the intake tract, dripped to the bottom of the runners, and is getting sucked into the valve ports. I actually saw this happen when I took the manifold off last night. After about five minutes of driving, the smoke is always completely gone.

 

The bad head gasket install was due to oil from the stud holes (poor prep) leeching in between the head and block during assembly causing a seal failure on the spark plug side. Leading to very slight coolant seepage on that side.

[Chemicalblue]

I have a little K&N filter on both my valve cover vent and the block vent. Never had an issue of smoke or oil leaking out of the block vent. It may help your issue going this way, but if oil is blowing out and not being pull out by vacuum TimZ may be right.

[cygnusx1]

There was a huge difference in the oil I was getting out of the PCV when I went to Megasquirt. I doubt it was a coincedence as I also eliminated the full PCV system designed by Nissan and am only using half of it. I think Proxlamus had the exact same observation if I'm not mistaking. I could try leaving both vented to atmosphere as an experiment but I really like the idea of PCV pulling the nastyness out of the crankcase. Just not as much as I'm getting. Besides, it never smokes under boost. Only smokes on engine cold, high vacuum driving, downhills, for about five minutes after start and then clears up. It doesn't smoke on startup either.

 

I will definitely experiment to see if it is blow-by. Thanks for the tips.

[cygnusx1]

OK I put the L28ET back together with the new head gasket and drove for a couple of days to make sure it's all good. I went back and retorqued the head, adding 5 ft-lbs for a total of 70. I retorqued the exhaust and intakes, which loosened up ALOT. I was still getting smoke puffs after a deceleration with the PCV hooked up to the block vent. Going down hills, I had to hold my breath or take it out of gear to minimize the smell of burning oil.

 

Tonight I plugged the PCV port in the manifold and left the block vent open. I went for a drive. After about 5 miles of driving, the oil smell was almost completely gone. No more smoke on decel, no more smell in the cabin. I even turned off the vent and had the side windows open about two inches. I would say the smell is about 90% better. I got on boost (15psi) took it to about 5000rpms and let off the throttle to coast down to about 1500rpms several times. No smoke, no oily smell.

 

I had visions of oil spewing all over my engine bay from the block vent when I got home. Popped the hood! NOTHING! Dry as a bone. Even put my finger inside the block vent hose and it was clean.

 

I need to do more miles to really test it further, but for now, I have confirmed that smoke on decel is from the PCV suction being too strong. It's not valve guides and it's not entirely blow-by.

 

Now I do want some sort of PCV, but I am DONE with feeding my intake manifold fresh synthetic oil!

[ktm]

Thats odd, because I pull over 20-in. of vacuum from a high rpm decel and my PCV system is hooked up as well. I do not smoke whatsoever.

 

Saying that, I want a catch can myself for the same reasons (blowing oil into my manifold!).

[cygnusx1]

Three things I can think of....

 

1.

Does the L28ET factory PCV valve limit suction? In other words it's a check valve that allows flow into the manifold but when the flow gets too high, does it act as a check valve in that direction as well? I seem to remember where the PCV valve in the L28ET at least, was not just a check valve, it's supposed to control flow in both directions. I could be wrong. If I am right, my PCV valve could be the wrong one, or not functioning correctly. (TONY D rings a bell on this one...I think he had a post talking about this in the distant past)

 

2.

Is your valve cover open to atmoshpere?

 

3.

The "filter/screen" inside my block might no longer be working or could be missing.

 

 

Hmmmmm.

[Careless]

Dave!!!! Daaaaaaaaaaaaaaaaaaaaaaaaaaaave!!!

 

I am fully with you on this one. MAN OH MAN how bad my intake piping was.

 

The previous stoner (I mean, uhhhh.... owner?! hey, his eyes were always red) never changed the PCV valve since the car was bought by the ORIGINAL owner. He said he kept ALL receipts, no matter how big or small the total was. I HAVE all the receipts... NO PCV Valve!

 

When i took my passenger side valve cover off, guess what BLACK SOOT all over the rocker arms and valve springs. ugly dirty scummy carbon deposity soot!

 

When i took the vacuum side/driver side off, guess what. NICE bronzing all over the valvetrain, clean as any whistle you'd put your mouth on! (ever see a referee blow a whistle that fell off their landyard? ewww guy, that's not clean! this valvetrain was KLEEN).

 

And my turbo? Compressor housing FULL of oil. That's how I KNEW it was not the rings. My engine has amazing bores still (like glass, but not a scratch!). My turbo rebuilder even made the comment (before i mentioned anything about my PCV mis-hap) that if the PCV valve is not replaced, the turbo does not suck in the oil properly and under boost it will actually spit the oil out back into the crank case. This is even worse than not using your turbo timer while driving leisurely around town (under hard driving it's SUPER BAD). The oil in there can be heated, but not for too long in the same spot, it has to move. If there is only a slight film of oil, it will wet the seals on the compressor housing and will lock them into an open position when the carbon buildup and heat dry out the oil film and create crud between seal/housing. Another way of oil getting into the turbo and intake pipe... through the turbo seal!

 

I put two and two together and figured that all the pcv valve was doing was washing the intake with oil under vacuum from the turbo at low rpm. Since the previous owner said he NEVER drove it hard, only when he first bought it... it makes complete sense. Stop and go vacuum all the time...

 

OR, my alter-excuse for the oily mess was that it was pressurizing the passenger head so much since there was no release for all that vacuum, that oil started to squirt in from the PCV rather than just blow-by gas. That would explain all the oil ending up RIGHT over the valve train on the intake springs on my car (V6, intake valves are closest to inside of engine, PCV DIRECTLY over intake valve springs, and goes into the intake directly above with an L shaped PCV hose, into the PCV valve right on the intake)

 

All in all, I ended up going from a clutch swap to an exhaust leak repair, to a manifold stud extraction, to a head removal, and now to a turbo rebuild... and you know what... Cost me a lot, but I'm glad I did.

 

I am SO Getting rid of that PCV system and running it to a catch can (Which I just made yesterday from a thermos )

 

The flame arrestor also shows up in the Nissan FAST for Z31's. Flame sounds like fire prevention, and back-fire arrestors are for oxy-acetalyn welding setups to avoid explosions, so it might be wise to find a new set of them and pop them in.

 

As for the PCV valve being a check valve.... YES. in the Z31 PCV valve (which makes it easy to see, since honda's and such are L shaped). There is a small ball bearing type moving piece inside that is spring loaded and under vaccum it is loose enough to be sucked in and mostly likely reveal small orifaces that would limit oil and send out just the blow-by gases. Under boost, the spring and intake pipe pressure force it closed.

 

At least that's how i think mine works from seeing it.

 

All this milarky happening with my car, but I'm learning a lot from seeing the ugliness that it once was :'(

 

Sure it's just going back to stock with a slight drivetrain upgrade and all new parts, as well as some head porting, but man... the small things create the biggest problems! I even found a friggen CARB JET lodged into the actuator vacuum line. No wonder this car was a rocket when I drove it (for 10 measly days! just enough for a taste of boost from my own vehicle...)

 

[Careless]

Now I do want some sort of PCV, but I am DONE with feeding my intake manifold fresh synthetic oil!

 

I solved that. (maybe? anyone else with turbo catch can experiences?)

 

Made a catch can. Pressure side of pcv system goes to intake on catch can. catch can goes turbo piping. Z31 turbo PCV valve on the line that goes to the turbo (so that under boost it closes).

 

catch can inlet has a tube on the inside that goes 1 inch above the bottom of the can. outlet side does not have a tube (keep them at different levels so oil doesnt just whisk around at the top or bottom and get sucked in easily.

 

bottom of can has a drain-cock with a large steel brake line that I am routing to an easy spot to fit a drain pan under so it doesnt drip on my engine bay.

 

inside of can also has a divider with perforations in it, and on the outlet side, the divider is stuffed with stainless steel wool, the curly ball kind not the #0000 Fine Grade polishing type. This stops soot or oily deposits from traveling up the side of the can and going to the turbo.

 

I think it's gonna keep my engine so clean, that I am going to go for a drive-clean test just to see how well my 87 gets compared to my friend's cars which are much older, even though my car is more than 20 years old and doesn't ever need to do emissions... I think having more power and keeping the environment cleaner is something to brag about !

[Careless]

and hey, at least you fed it synthetic instead of dyno oil. I mean, the engine probably likes the taste of the newer stuff, not the 65 million year old stuff. There should be an expiry date on it!.

 

My engine is going to have to ration whatever it can get from the catch can if it wants to eat oil this time around.

[cygnusx1]

I am going to go shopping for an aluminum can, some hose, some fittings, steel wool, clamps, a new PCV valve, and fab up a bracket for a catch can where the windshield washer bottle used to be.

 

I bought a catch can off of ebay a while back but it's too big.

[WizardBlack]

IMHO blowby on turbo cars is the nature of the beast. Just as you guys are doing, I'd suggest throwing a catch can on it and keep going. All the turbo 4 bangers I've tuned use them. You'll know when it's something else blowing oil that shouldn't. Heck, some of the fastest 4 cyl. turbo cars blow a quart of oil in one single digit pass.

[Tony D]

On a high revving N/A 3.0L engine, a 0.63" orifice in the block hole to the manifold vacuum log was more than enough evacuation (with a K&N Filter on the top of the valve cover, or ducted to the intake filter housing for fresh-air makeup).

I think this is the same size JeffP put into his turbo car after we discussed it. Jeff went with a catch can/oil separator to prevent buildup in the intake as well.

 

If you look at the Z32TT, they are notorious for a poor PVC oil vapor separator. It's not uncommon for them when run under boost hard and often to puke the intake full of oil to the extent that it starts damaging things---if not looking like mosquito abatement in the third world.

 

For any pressurized / vacuum system, the larger area of capicitance the smaller vacuum or pressure source you need to bring it to a given pressure vacuum.

 

Usually when setting one of these up, you will put in a coalescant to knock down the vapor to droplets that won't be entrained in the airstream back to the intake manfiold. This lets you use a non-restricted vacuum line for maximum evacuation when it's needed.

 

The Mitsubishi PCV's (some of them) use a restricted PCV, but not the datsun.

 

Coincidentally, the .063 Orifice for the Mitsu PCV is pretty close to the same idea GM used on the Corvair---it's tube has a .100" hole in it down the tube, and it fed to the air cleaner and the base of both carbs.

Adding volume in the form of a separator tank will give you more time on-boost before pressure comes to a level where it causes leaks or pukeover, and will take slightly longer with a restricted vacuum source to recover to true vacuum.