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[Datsun 1200 encyclopedia]

Cylinder Head Identification

From Datsun 1200 Club

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Categories: Engine Mechanical | Cylinder Heads

At first glance, all A-series cylinder heads look alike. But by careful notice of specific features you can identify the model.

Contents

Overview

For the cylinder head, the best way to tell which head you have is to check the casting number in the valve train area (remove the rocker cover to look for this number).

If the head you are looking at does not have a casting 
number, see the next section: Distinguishing Features.

Once you have the casting number, see Nissan Part Number Prefixes for a table of the different model to part numbers. For example, H23 means the part was originally designed for B110 GX models.

  • A10 may have "180", "H01", "257", "H03" or no markings at all
  • 1971-1973 A12 may have "180", "H10" or "H39". Some have no markings at all.
    3794.jpgAlbum click to view
  • A12 GX may have "H23" or "230"
  • 76 Sunny trucks (A12) may have M30, G25, G61
  • 1974 A13 may have "H62" or "620"
  • A14 could have several different ones, such as G32, H72 (or 728), H74, H75, H77, H78, H85, H92 or H98 depending upon year, country, and emission control design.
    5254.jpgAlbum click to view
  • M24 or 246 is A14T (Hitachi Twin Carb engine)
  • H85 is A12 or A13 (newer engines)


The casting number will be the first 3 digits of the last half of the part number, as all cylinder head part numbers begin with the same 5 digits (11041). For example:

11041-H2300 or 11041-H2301 HEAD ASSY-CYLINDER A12 GX
* 11041 is the base part number for all cylinder heads
* "H23" means the part was first used on the B110 GX vehicle.
* "728" is short for H728x, indicating a B210 "H72" part

references:

ID Marks

You may find many marks/engravings/casting numbers on a cylinder head. Original A12 heads have no marks. Remove the rocker cover to see the key marks.

These are the important marks:
26064.jpgAlbum click to view

For example, this head has rear mark 'H75'
6292.jpgAlbum click to view

Look up the Type mark at A-series Cylinder Heads

The front Mark can sometimes help further identify the head.

Early or Late?

To determine if the cylinder head is from a pre-1974, or 1974-onwards engine, check for the presence of an oil passage, located here:

15689.jpgAlbum click to view
Only pre-1974 engines will have this passage in the cylinder head, from factory. It is, however, possible for this oil passage to be drilled on a 1974-onwards engine. But it is a good indicator nonetheless.

For verification of an original, pre-1974 cylinder head, inspect the cylinder head for the following:
4588.jpgAlbum click to view
Pre-1974: Oil passage boss.

8122.jpgAlbum click to view
1974-onward: No oil passage boss present.

Distinguishing Features

Any A-series cylinder head can be bolted onto any A-series engine block. However, compression ratio, port size (oval port, and round port), and manifold stud pattern need to be taken into consideration. Naturally, it is best to match port type, and size (e.g round port manifold, and round port cylinder head). The most critical difference, is the rocker shaft oil passage. It was relocated in 1974, as part of the A-series engine redesign.

Cylinder head oil passage

An extra oil passage in the cylinder head is required, for some engines. For pre-1974 engines, ensure your head gasket has the corresponding hole! You can punch, or drill, a hole in the head gasket if necessary.

Missing hole
25871.jpgAlbum click to view

A12 head gasket
22067.jpgAlbum click to view

22073.jpgAlbum click to view

Top: 1974, no oil passage. Bottom: 1973, with oil passage.
15689.jpgAlbum click to view

The older 1967-1973 head has the oil passage:
4587.jpgAlbum click to view

Boss, on the exterior, for cylinder head identification.
4588.jpgAlbum click to view

Comparison to 1974-onward cylinder head: no oil passage. The newer, redesigned engine has the oil passage in the engine block instead.
8122.jpgAlbum click to view

Late blocks do not send the oil up through the small passage, so do not need the hole in the gasket. Instead oil flow through the head bolt hole. So late blocks can work with either old or new heads. See Block_Comparison#Head_Oiling

Factory installed brass plug in late block
20443.jpgAlbum click to view

Interchangeability

Any cylinder head old or new can be used with old or new engine.

  • A pre-1974 cylinder head will bolt onto any engine block, with no modification required.
  • A 1974-onward engine block will work with any cylinder head. But, in the case of bolting a 1974-onward cylinder head to a pre-1974 engine block, a minor oil passage must be created.

27011.jpgAlbum click to view

Method 1:

I took off the head, marked it with the old head gasket, and drilled it on a 45 angle. junior

Method 2: Cut the head gasket between the oil feed hole and the center head bolt hole:
174_59a79dec6c22b.jpgPost click for topic

Method 3:

I have seen a crude system where a 1200 head gasket was placed on the head to determine the position of the oil feed hole in the block. This was centerpunched & a very shallow hole was drilled. [about 1 to 1.5mm] then an angle grinder was used to grind a small trench across the gasket face to provide an oil passage froom this shallow hole to the nearest head bolt hole.

Crude as hell, but it worked. A very steady hand would be a prerequisite.

Personally, I would suggest a milling machine if this method is used.

question about oil blockage

Combustion Chamber

All Datsun A-series production cylinder heads have a wedge-shaped combustion chamber. However, most USA models are equipped with a cylinder head that is open-chambered, for lower NOx emissions. The 'heart-shaped' combustion chamber has a superior power output due to the closed-chamber design, with a large quench area.

3795.jpgAlbum click to view

  • A,B: Heart-shaped high-compression chamber - good for high-octane gasoline.
    Also known as closed-chamber, peanut-shaped, butterfly-shaped or kidney-shaped.
  • C: 360 open chamber, for reduced emissions.
  • D: Bathtub chamber (from 1982 Sunny Truck G61 head).

Any combustion chamber design will work on any A-series engine.

Comparison - Closed Chamber vs. Open Chamber
26426.jpgAlbum click to view th_PICT0370.jpg

20539.jpgAlbum click to view
Comparo

Open Chamber (small CC, high compression, but nevertheless an open chamber)
11417.jpgAlbum click to view

Chamber Size

See also: Compression Ratio
  • A12 closed chamber: 27-29cc
  • A12T: (M08 head) 32 +/- .5 per 1981 Nissan Racing book
    • for 11:1 with GX flat-top pistons, GX headgasket,
    • mill head 0.9mm (0.035 inch) for 25.6 cc
  • A12 GX: 29.1 cc (as per FIA papers)
  • H75: 31cc
  • H89: 29-31cc
  • H92: 31cc (A14E head) 29.1 +/- .5 per 1981 Nissan Racing book
  • H95: 35cc (A15 dish: 6cc)

See CCing

Intake Ports

  • Round - Best for low-RPM operation (more power under 4,000 RPM)
    1233.jpgAlbum click to view 6119.jpgAlbum click to view
    All A12s, later A13s, some A14s, and (reportedly) Vanette A15s.
  • Small oval (28 mm x 30 mm). The 1974 A13 has this design.
  • Small oval, with swirl obstruction. These are better for emissions and fuel economy (H95 head, 1981-1982 USA all engines)
    4444.jpgAlbum click to view
  • Regular oval (28 mm x 34 mm). These standard A14/A15 ports are best suited for high-RPM operation, or for the larger displacement engines.
    26285.jpgAlbum click to view 14888.jpgAlbum click to view 14886.jpgAlbum click to view 12714.jpgAlbum click to view
    NOTE: the top of the port comes up to the centerline of the top manifold studs.
  • ^Regular oval (28 mm x 34 mm) notched for injectors. A14E/A15E 92HP engines
  • Large oval (GX and A12T, 30 mm x 36 mm). From A12GX Engine and B210 or Cherry A12T engines.
    4441.jpgAlbum click to view 9028.jpgAlbum click to view 12131.jpgAlbum click to view
    NOTE: the top of the port comes up as high as the top of the top manifold studs (port comes up past the manifold stud centerline).
^
The cylinder head for the A14 EFI engine has less intake and exhaust resistance.

Datsun Competition Tune-up Manual model N10 Series (March 1982 Pub. No. CT2E-0N10P0)

GX Oval vs. A14 Oval Comparison.
5215.jpgAlbum click to view
Top: GX ports go much higher than A14/A15 ovals.

Port Shape

Early head with oval ports is either an A12GX head, or its twin, the early A12T head from the Nissan Cherry (E10). These are the high-revving heads for the factory Hitachi Twin Carb engines.

Exhaust Ports

All heads have nearly square exhaust ports.


th_469.jpgAlbum click to view

Intake Ports

* Round port 28mm: A12
* Round port 28mm lowered: A14 GFU
* Small Oval port 28x30mm: A13, A12A
* Medium Oval port 28x34mm: A14
* Large Oval port 30x34.5mm: A12GX Engine

Port Sizes

PortsSize (mm)ExhaustRaisedNote
round2827x26no1971 A12
round28?lowered1977 GFU
Oval - Small28x30?no1973 A13
Oval - Medium28x3228x26noA14E, A15E
Oval - Regular28x3428x26noMany A14s
Oval - Large (GX)30x35 - 3627x29 or 28x26YesA12GX (1971-1973)

GX extra-large oval ports (36 mm tall)
DSC04878.jpg

20540.jpgAlbum click to view
Port Comparison

Wet, Dry Intake Manifolds

Coolant passages are below the intake ports (present or not). If present, they can be large holes or small holes.

See main article: Water Ports

4441.jpg 4444.jpg

Intake/Exhaust manifold bolt pattern

Early A12 differs from the A14. A12 changed in 1976, but A12 Wagons and Trucks continue to use the old pattern until 1979-1980.

982_.jpgAlbum click to view

Top: New bolt pattern
18992.jpgAlbum click to view
Bottom: Original bolt pattern

The bolt pattern on the cylinder heads also differ. early A10/A12 heads are only drilled for the older pattern. Newer A12 (1980s/1990s) are drilled for newer pattern. Some newer heads are drilled for both.

4440.jpgAlbum click to view
Bolt pattern

Valve Springs

The following A-series heads had dual valve springs. There is a small-diameter spring inside the main spring.

So dual springs are a good indication of a special head, but not conclusive. You will need to check the intake port sizes and other features to make a final determination.

Valves

All A-series engine use valves with 8mm diameter stem
ValvesIntake Part No.In. SizeExhaust Part No.Ex. SizeLength
A10, early A12, late A12 Van13201-H100035mm13202-1800029mm103.8
A12GX/A12T13201-H230035mm13202-H230029mm103.8
Late A12, A13, A12AS13201-H230035mm13202-H740029mm103.8
A13(1974),A14 & A1513201-H620037mm13202-H6200, 13202-H890030mm103.8
A12A, A14, A15 1981-82 USA13201-H950035mm13202-H950030mm100.0
A12A, A14, A15 1981-82 canada13201-H620037mm13202-H620030mm103.8
Nissan Competition tuliped99996-H110037mm99996-H110030mm103.8

A12GX Identification

A true A12GX cylinder head has all these features:

  • Dual valve springs
  • No casting numbers
  • Large Oval port 30x34.5mm. These ports are raised, and extend above upper intake bolts
  • 27x29 mm exhaust ports
  • closed combustion chamber - heart shaped, large size combustion chamber of 29.1 cm3
  • large water holes (one under each intake port). Each hole is about the diameter of a pencil (non-GX heads have small holes)
  • Seven upper intake face bolts, nine bolt holes (vs only 5 for other pre-74 heads)
  • As with all pre-74 heads, Oil passage on head face (spark plug side), oil boss on side face between plugs 2 & 3 just above head face
  • SAME valve sizes as standard A12: 29mm exhaust, 35mm intake
  • NO bosses on sparkplug side between 1&2 and 3&4

One way to identify a GX, when the head is still installed: Look for the oil passage boss (indicating an early head), and for seven studs on the top of the inlet/exhaust manifold gasket. This combination is a good indicator of an GX (or early A12T) head. Regular early heads have only five studs along the top of the gasket.

  • 5 mm water ports below the intake ports
  • closed chambers
  • oil hole between push rod holes for Nos. 2 & 3 cylinders

Early head with oval ports is either an A12GX head, or its twin, the early A12T head from the Nissan Cherry (E10). These are the high-revving heads for the factory Hitachi Twin Carb engines.

GX and A12T (non-GX) heads have small bulges on the top side (for the raised manifold bolts):
23095.jpgAlbum click to view

Datsun Competition heads have raised ports ceilings visible on the top face.

A12GX vs A12T

Datsun B210 twin carb A12 engine (A12T) uses a cylinder head nearly identical to A12GX. Differences include:

  • Block face missing oil passage hole on B210 head
  • Spark side threaded boss for B210 fuel rail
  • Front side threaded boss for B210 high-mounted alternator bracket
  • Rear face: no obvious differences
  • Manifold face: no obvious differences

26105.jpgAlbum click to view 26106.jpgAlbum click to view 26107.jpgAlbum click to view 26108.jpgAlbum click to view 26109.jpgAlbum click to view

Head Front Face

3-bolt
1293.jpgAlbum click to view

5-bolt
776.jpgAlbum click to view 13032.jpgAlbum click to view

Block-off plug for AIS hole
PICT0378.jpg

Block-off plate for AIS hole
23098.jpgAlbum click to view

Spark-side Bosses

Look at the accessory/bracket mounting holes to help identify a cylinder head.

Variations
* No bosses
* One boss (between #1 and #2 near top)
* Two boss (between 1-2, 3-4)
* Three boss (between 1-2, 3-4, plus a front boss)

H85.jpg

The bosses are used on newer engines for the fuel rail and Air Injection/Air Induction (EAI) pipes.

Three boss. Two top bosses and a front boss
8122.jpgAlbum click to view

Three boss with oil passage
22086.jpgAlbum click to view

No bosses. A10 or Early A12
18298.jpgAlbum click to view

No bosses. Early heads used a fuel rail that bolts to the valve cover
4588.jpgAlbum click to view

One boss (undrilled)
15690.jpgAlbum click to view

One boss (drilled):
3640.jpgAlbum click to view

Two boss (example: G25 sunny truck head 1979-1989 and G61 1989-1994)
26231.jpgAlbum click to view

Air Induction (EAI) Pipe Brackets (B310.A13 shown)
AIStubes.jpg

AIStubes_.jpg

Manifold-side Bosses

Variations
* No boss
* Front boss only
* Rear boss only
* Both Front and Rear bosses

In addition, bosses can be present but not drilled & tapped. For example, an H72 casting can be processed either way (drilled or undrilled). The difference merits a different Part Number, for example H72 casting part number 11041-H7200 and H72 casting part number 11041-H7240.

Front Boss location
head_boss_1.jpg

Various fittings can be inserted: Plugs, switches or valves
8226.jpgAlbum click to view

Rear boss location
head_boss_2.jpg

No Boss

Without boss, early A14
469.jpgAlbum click to view

Without boss, 5-bolt face:
2547.jpgAlbum click to view

Undrilled Boss

A12 with boss, not drilled (late B110)
4587.jpgAlbum click to view

A14 with front boss undrilled
5215.jpgAlbum click to view

Front Boss Drilled & Tapped

With boss (fitted with vacuum switch in this photo)
14137.jpgAlbum click to view

Late A12
1233.jpgAlbum click to view

Front and Rear Bosses

Both bosses drilled and tapped (H72 107 industrial A14)
11415.jpgAlbum click to view

With rear boss not drilled, front boss drilled
2983.jpgAlbum click to view

Blank rear boss, tapped front boss
6290.jpgAlbum click to view

With rear boss drilled, front boss undrilled
5249.jpgAlbum click to view

5250.jpgAlbum click to view

Rear Boss Only

With rear boss (no front boss) H89

1234.jpgAlbum click to view

Alternator Mounting

Also see: Alternator mounting

Left Side

Early A-series engine (front distributor) mounted the alternator on the left side of engine, because the distributor and oil pump are on the right side.

  • B10,B110,E10: on left side of engine, down low
  • Upper bracket bolts to front face of head

15170.jpgAlbum click to view 7891.jpgAlbum click to view

Right Side

Late A-series engine moved the distributor to mid-block, freeing up room for a right-mounted alternator.

  • B210, some B310: up high
    • Upper bracket bolts to Upper bolt hole on head

200balt.jpg

  • Some B310: up low
    • Upper bracket bolts to lower bolt hole on head

3265.jpgAlbum click to view

Rear Face

Left bolts, low water outlet
Photo0725.jpg

Mid-bolts, high water outlet
18300.jpgAlbum click to view

Undrilled bolt bosses
IMGP2332_convert_20101014150748.jpg

16432.jpgAlbum click to view

Air passage head casting H72 (air passage might not be drilled)
22084.jpgAlbum click to view

Visual ID

See Cylinder Head Index 

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