l20b block pipe

[DATSUN671]

i recently broke a pipe on the l20b block...i was wondering what its for and is it important for the engine...

 

thanks for the help

[JoeCool]

Got a picture of the pipe?

[Jayden71]

:confused:

[datzenmike]

Only pipe on the block I can think of. It's the block vent. The PCV valve in the intake uses a small amount of vacuum to draw corrosive combustion, moisture and gas/oil fumes from inside the engine. Without it the oil is contaminated sooner and needs changing. (of course no one does this) So the motor gets dirty inside and bearings don't last as long. Every effort should be made to keep this system functioning.

 

[DATSUN671]

is it okay to block it off

[racerx]

I think tthere for a reason,a smentioned earlier.  Maybe you can weld another piece to it.

[king bee66]

dont block it off.  if you can get a grip on it, spray some pb blaster on it and work it side to side.  may take some time but it will come out eventually.  you may also be able to wedge a slightly smaller pipe into its place

[DATSUN671]

so where does the pipe connect to....when i take it off what do i do next...theres no where i can connect the pipe....im running side drafts...

 

what will happen if i block it off

[kelowg]

U well pressurize the crankcase,blewing oil out most of the seals. At the very least,fit a valve cover style breather/filter.

[datzenmike]

so where does the pipe connect to....when i take it off what do i do next...theres no where i can connect the pipe....im running side drafts...

 

what will happen if i block it off

 

Answered

 

Only pipe on the block I can think of. It's the block vent. The PCV valve in the intake uses a small amount of vacuum to draw corrosive combustion, moisture and gas/oil fumes from inside the engine. Without it the oil is contaminated sooner and needs changing. (of course no one does this) So the motor gets dirty inside and bearings don't last as long. Every effort should be made to keep this system functioning.

 

 

With nowhere to go the fumes will blow out the valve cover vent hose making a smelly mess. Any inside will condense at night when cooled and mix with your oil..

 

Side drafts are a problem. Put a hose on the vent pipe and run down low beside the block so fumes don't get into the car...  is about all you can do. Change oil more often.

[banzai510(hainz)]

what will happen if i block it off

 

 

Its there to vent the block. Dont BLOCK IT OFF, What you thinking.

 

I just have the tube point out and leave it open. when running sidedrafts. if you motor is really worn out its will stink at idle.(blowby)
 

[racerx]

show us a picture where it broke off....hard to determined what can be done w/out pics.

[Silky_Johnson]

Here's a picture of what I did on my sidedraft setup.  I have found that, per Mike's statements, the oil is staying a LOT cleaner for a LOT longer.  Two months after an oil change, the oil is still so clear that I can barely see it on the dipstick.  Previously, I had no PCV setup, and the oil was always black as night.

 

 

It really all depends on what intake you are using.  I think the SU intake is already tapped for the PCV valve directly, and I'm pretty sure the cannon intakes don't have any ports?  The Mikuni manifold worked out well for me because it has the two ports on top that distribute evenly to all cylinders, which is what you need.  I got all my hose fittings from McMaster-Carr.  I also have a spare L20B block pipe, but shipping to Guam might be cost prohibitive?

[racerx]

I think the pipe is pressed in.  You may be able to try to unscrew it out.  I can be wrong...but what I did whenI installed my L18 is measure the old pipe from L16 and went to Ochard supply and found a pipe that fits and tapped it in.

[king bee66]

seems like if you left it open youd be doing a fair amount more changing oil, as well as leaving a trail of oil where ever you go

[datzenmike]

L16/18 come out from side of the block... L20B come out the top like my picture.

 

 

I know it's easier to just let the fumes dump out but I really like how someone made this PCV system look so elegant. When I see stuff like this I just smile. It's so nice to see nice sensible work. Couple of feet of hose and a few fittings... no excuse for not doing the same.

 

[bonvo]

mike was close very close to your solution

 

early on in the automotive industry vehicles didnt have a pcv system they had what was called a downdraft tube it used vacuum created by the air running under the vehicle to perform the same job as the pvc system 

 

this is my 56 chevys downdraft tube

 

since your side drafts have no prevision for a pvc set up take whats left of your current tube out and make a new one that bends down and out towards the transmission you want the pipe a little lower then the lowest object and cit it level with the frame rails this will solve your issue you will still have to change the oil more often but this is the closest you will get to the stock pvc system

[king bee66]

Bonvo,

I'm pretty sure that that's still how the vent works, its just now the oil and fumes have a place to go. If you disconnect the PCB valve and press the throttle you can see oil coming up from the hose, the valve just puts the fumes back into the mani without and closes when you throttle to keep the oil out.

[bonvo]

thats exactly how it works what im saying is that since he no longer has previsions for a pvc system going back to what they had before the pvc system was around could be the solution the the problem he is having

[datsunaholic]

Sort of the same job.  The PCV had 2 functions, as said above:

 

1) The main function was to eliminate Crankcase ventilation emissions, as it all vents through the intake manifold and gets burned.  That's cleaner than letting it dump to the street.  It also maintains constant circulation, though the draft-type dump tube did the same thing as long as you had an upper breather as well.  But by using manifold vacuum, it has  a constant source of vacuum, particularly stopped, so it doesn't rely solely on blowby to increase crankcase pressure above atmospheric.  Instead, the crankcase simply has to be above manifold pressure.

 

2) It also keeps moisture out of the crankcase.  When you shut an engine off, everything goes to atmospheric equilibrium immediately.  But the engine is hot inside.  As it cools, it pulls outside air in.  With a dump tube pointing down at the street, what happens when you park on a rainy night on wet pavement?  Yup, it draws damp air in.  This forms condensation inside the engine.  Condenstation which ends up in the oil, making it acidic. Doesn't even have to be rainy; if it's not Arizona, simple atmospheric humidity will introduce water in.  This is one of the reasons engines prior to the late 60s had a LOT of trouble with erosion/oil burning long before they reached 100,000 miles.  Wasn't the only reason, but the PCV's relatively closed system (plus having the top breather coming from the air cleaner) cut the amount of moisture by a lot.  And having vacuum at one side of the PCV, the reduced pressure inside helps "boil out" the water from the oil much faster than a simple atmospheric dump tube.

[datzenmike]

The PCV valve is spring loaded so gasses can only go one way. That's into the intake. This is only so that if there is a carburetor back fire there is no chance of any flame possibly igniting block vent fumes. As long as there is intake vacuum the PCV is open. It may flutter but is primarily open. Below the block vent is a baffle and a large wad of rolled up fly screen. Any fog of oil droplets is caught in the screen forms drops that fall back into the crankcase by their own weight. Only fumes can rise high enough up the block vent to get sucked into the intake.

 

 

PCVs were installed on most cars around '62. I remember as a kid being down town (near the liquor store) and some guy had flooded his car trying to restart it. It was summer, hot, probably vapor locked... maybe the guy had been drinking. You could hear the starter cranking and cranking, he was probably pumping the gas, when BANG! Smoke pouring from under hood. The gas fumes from the flooded cylinders exploded in the crankcase. Blew the six cylinder valve cover up in a W shape held on by the screws. Bent the oil pan to shit too.

[datsunaholic]

Yeah, you shouldn't have oil coming out the PCV tube.  That's a sign that you've got serious blowby or the baffle is missing (because then the oil is being slung up the pipe by the crank throws).  I've had 2 guys come by with their air cleaners full of oil (from the valve cover vent) and when it's doing THAT, the engine isn't long for the world.  You will see some oil mist, so the tube won't be totally clear, but the cars I have that had serious oiling in the PCV line?  All well over 200,000 on the engines.

[king bee66]

Im on my phone right now so maybe I over looked part of the conversation but having oil in the hose doesn't mean you have blow by because as soon as you press the gas the pressure from the crankcase seals the valve. The crankcase is only venting when the pressure coming up the hose isn't great enough to seal the valve.

[bonvo]

i never said it was a replacement for the pvc i said that since he cant run one due to his intake set up this might be the best option unless he wants the ghetto looking pvc set up on the last page 

[datzenmike]

Im on my phone right now so maybe I over looked part of the conversation but having oil in the hose doesn't mean you have blow by because as soon as you press the gas the pressure from the crankcase seals the valve. The crankcase is only venting when the pressure coming up the hose isn't great enough to seal the valve.

 

 

 

Not how a PCV valve works. Basically its a very small hole like 1/8" with a small ball held against it by a spring. A light spring. You can take the PCV valve off and shake it and hear the ball rattle. When on the intake it is normally held closed by the spring, but when the motor starts, vacuum pulls the ball back against the spring and begins sucking fumes out of the block vent pipe. It's basically open when the motor is running. 

 

The ball and spring are only there to prevent a backfire flame from traveling back down the tube. Positive pressure from a backfire will shut the PCV valve.

 

 

i never said it was a replacement for the pvc i said that since he cant run one due to his intake set up this might be the best option unless he wants the ghetto looking pvc set up on the last page

Jon that is not a getto set up. It's neat and functional.