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[Datsun 1200 encyclopedia]


From Datsun 1200 Club

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Category: Emission Control And Tune-Up

Positive Crankcase Ventilation (PCV) was the very first of the emission controls (1964). It aims to prevent the crankcase from dumping fumes right into the atmosphere. This is a good system, and can actually help power and fuel economy. Before 1964, cars had a 'breather pipe' that led from the block down to the underside of the car. Normal blowby gases were thus simply vented to the air. Worse yet, when the piston rings became worn, a visible trail of smoke could be seen eminating from the bottom of the car. Not only did it pollute, but didn't smell good either.



The PCV system consists of three components:

  1. Simple vacuum-operated valve connected to the intake manifold
  2. crankcase breather hoses:

Upper breather hose connects to bottom side of air cleaner
PCV_upper.jpg 27052.jpgAlbum 27052

Lower breather hose

The PCV Valve threads into the intake manifold
26135.jpgAlbum 26135

Black (lower) hose is the main PCV hose. On the manifold end it connects to the PCV valve. The other end goes to the engine block breather pipe.
4847.jpgAlbum 4847

H39 upper hose contains a "flame arrestor", so generic hoses should not be fabricated. A new hose is available from Nissan. 11826-H3900 was used starting July 1971.
13527.jpgAlbum 13527


As part of your Tune-up, replace the PCV valve if it:

  • oil-soaked or crusted with sludge (sometimes it can be cleaned with ether spray or carb cleaner). The valve inside should open and close when you shake it back and forth
  • Has a broken spring. The valve inside should close at rest, even if you hold it straight
NOTE: A stuck PCV valve is a vacuum leak (if stuck open). It can cause a high idle or uneven idle.


Nissan calls its PVC system the "Crankcase Emission Control System", as it cleans up emissions with no loss of power. PCV system is a good thing.

Fumes are thus routed to either 1) air cleaner when engine speeds are high and so able to 'suck' the fumes in or 2) intake manifold when idling where vacuum is high and so opens the valve slightly and pulls the fumes out of the crankcase. This is where the efficiency comes in. Since at idle the pistons are operating under low vacuum, the PCV valve equalizes the forces in the crankcase, hence less oil is sucked into the cylinders at idle.

PCV system

Datsun 1200 GX engines routed the hoses in a different manner. See A12GX Engine.

Also see:
Breather Tubes
The 1982 Factory Service Manual says:

The positive crankcase ventilation (P.C.V.) valve is provided to conduct crankcase blow-by to the intake manifold.

During partial throttle operation of the engine, the intake manifold sucks the blow-by gas through the P.C.V. valve.

Normally, the capacity of the valve is sufficient to handle the blow-by and a small amount of ventilating air.

The ventilating air is then drawn from the carburetor air cleaner, through the hose connection carburetor air cleaner to rocker cover, into the crankcase.

Under full-throttle condition, the manifold vacuum is insufficient to to draw the blow-by flow through the valve, and its flow goes through the hose connection in the reverse direction.

On cars with an extremely high blow-by some of the flow will go through the hose connection to the carburetor air cleaner under all conditions.

Non-stock Air Cleaner

If you are not using a factory air cleaner, the upper ventilation hose can still be connected.

To retain the positive ventilation:

  1. Buy a hose adapter at your local auto parts store
  2. Drill a hole in the air cleaner, inside the filter area
  3. Attach the rocker cover hose to the air cleaner

Like this white angle adapter included in the Weber 32/36 kits

Some convert to a non-positive fume system, by venting the rocker cover. If the PCV valve is left in place, this acts positively at idle and low engine speeds, but not at high speed.
10871.jpgAlbum 10871

Race Car

Race cars are often required to use an oil/vapor separator instead of, or in addition to, the PCV valve. The main purpose of this racing requirement is not to increase performance, but to control oil spills onto the race track surface. Worn race engine may generate massive amounts of engine blowby and push oil out of the breather and into the environment.

See main article: Oil Catch Can

GX Ventilation

A12GX Engine breather hose routing is the opposite of a regular A12 engine.

A12 single: rocker cover to air cleaner
            block breather tube to manifold
A12 twin:   rocker cover to manifold
            block breather tube air cleaner

The GX engine has a reverse flow block ventilation system, compared with the standard A12 engine. In the GX, the block breather hose goes to the air cleaner, while the rocker cover hose goes to the intake.

8995.jpgAlbum 8995 18250.jpgAlbum 18250

Block "pipe connector" (breather tube) connects to the air cleaner
14541.jpgAlbum 14541

A10 Ventilation

A10 Engine in the Datsun 1000 did not have a PCV system. Instead, it relied on passive breathing — as did all cars before the positive system was developed.

A10 engine block breaths through the oil filler cap. The cap is ventilated (not sealed like the A12 oil cap).
15099.jpgAlbum 15099

This system did not draw the air out during idling, so over time the fumes got sludgy inside the engine. Even so it was not a big problem. At higher engine speeds, the airflow into the carburetor pulled air out of the block.

No breather tube — A10 from Datsun 1000
17129.jpgAlbum 17129

One improvement to be made is to connect the rocker cover via a hose to the air cleaner. In this way air is drawn up out of the engine. (J15 engine pictured)
15633.jpgAlbum 15633

Back of rocker cover connected to air cleaner
6547.jpgAlbum 6547


Same as all Datsun (L/A/VG/U/R/CA/Z/E/J), many Nissan (including GA) and Subaru 1998-2002 2.5.

Part Numbers

26135.jpgAlbum click to view
1.64 in. height
0.69 in. outlet
0.75 in. O.D.
NPTF thread pitch
* Purolator PV1019
** Purolator PV1016 has same dimensions but flow differs
Aftermarket buy at
* FRAM FV263 
* Standard Motor Products V184T or V184 $2.19
* Beck/Arnley 0450031
* Airtex 6P1056 or PCV2 $2.93
* AcDelco CV1016C or 25173530 

PCV Valve, from $2.00 - $7.50. Available everywhere

PCV Valve: FRAM FV263 $1.73
           BECK/ARNLEY 0450031 $2.24
Infiniti 1993-1997 J30
Subaru 1998-2002 FORESTER 2002 IMPREZA
1971-1973 1200
1972-1979 620 PICKUP 
1966-1970 1600
1974-1977 710 
1968-1970 2000 
1980      720 PICKUP
1977-1986 200SX
1983-1986 720 PICKUP
1979-1982 210
1977-1981 810
1970-1973 240Z 
1974-1978 B210
1975-1977 280Z 
1986-1989 D21 PICKUP
1979      280ZX 
1976-1978 F10 
1990-1996 300ZX
1982-1984 MAXIMA
1979-1982 310
1987-1989 PATHFINDER
1967      411
1983      PULSAR 
1968-1973 510
1983-1990 PULSAR NX
1978-1981 510
1982-1990 SENTRA
1965-1968 520 PICKUP
1982-1986 STANZA
1969-1972 521 PICKUP
1988      VAN 
1973-1976 610 

FRAM FV263 interchange
* Nissan 
* AC-Delco CV941C

Nissan 11810-A3500 <2> 11810-A3501
* 1983-1983 B11 with E15S/E16S engine 
* 1979-1981 N10 with A14S/A15S engine
* 1983      N12 with E16S engine
Nissan 11810-A3501
* 1982-1988 B11 with E15S/E16S
* 1988-     B12 with GA16I
* 1986-1988 B12 with E16S/E16I
* 1989-     KN13 with GA16
* 1987-1988 KN13 with E16
* 1988-1989 KN13 with CA18D
* 1987      KN13 with CA16D
* 1983-     N12 with E16S


Emission Control Part Numbers

11826-H1900 HOSE-ROCKER COVER TO AIR CLEANER 1070- <> 11826-H1000
11826-H3900 HOSE-ROCKER COVER TO AIR CLEANER 0771- <x> 11826-H1900
* for use with ATC heated Air Cleaner


8710_56e620500cb63.jpgPost 477180 

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This page has been accessed 37,655 times. This page was last modified 23:05, 27 November 2021. Content is available under Datsun 1200 Club.