![[Datsun 1200 encyclopedia]](/wiki/upload/wiki.png)
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.
-
- 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.
-
- 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:
- Nissan Part Number Prefixes
- Discussion: Various cylinder heads
- Discussion: A14 head--728-402
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:
album
For example, this head has rear mark 'H75'
album
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 head is for an early (pre-1974) or late (1974-up) engine, check for existence of an oil passage here:
Only early engine have the passage in the head here. Of course, one can have the passage drilled on a newer head, but it is a good sign.
To double-check it is an original early head, look at the outside:
Early head: oil passage boss
Late head: no oil passage boss
Distinguishing Features
Any A-type cylinder head will bolt onto any A-type engine. However compression and intake ports are big consideration, as are the manifold bolt patterns. For best results, match port types (e.g. round-port manifold on round-port head). The most critical difference is the rocker shaft oil passage. It is in a different place between early and late engines.
Oil passage in the head
An extra oil passage in the head is needed for some engines. For early engines, make sure your head gasket has the hole! You can punch or drill a corresponding hole in the head gasket if needed.
Missing hole
Top: 1974, no passage. Bottom: 1973, has passage.
The old 1967-1973 head has the oil passage:
album
Boss on outside identifies the head
album
Compare to newer head: no passage: The newer engine has the passage in the block instead.
album
Interchanging
- Pre-1974 heads fit on all engines with no modifications needed.
- 1974-up block works with any head. But for newer head on older block, an oil passage must be drilled.
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:
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 heads use a wedge-shaped combustion chamber. However most USA model are open-chambered for lower NOx emissions. The 'heart-shaped' combustion chambers have superior power due to their closed-chamber design with large quench area.
- A,B: Heart-shaped high-compression chamber is good for high-octane gasoline
- a.k.a: closed chamber, peanut-shaped, butterfly-shaped or kidney-shaped
- C: 360 degree open chamber for reduced emissions
- D: Bathtub chamber (from 1982 Sunny Truck G61 head)
Any combustion chamber design can fit on any A-series engine.
Comparo - Closed Chamber vs. Open Chamber
Comparo
Chamber Size
Also see: Compression Ratio
- A12 closed chamber: 27-29cc
- A12T: (M08 head) 32 +/- .5 per 1981 Nissan Racing book
- for 11:1 with GX flattop 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: These are best for low-RPM operation
-
- All A12, new 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 good for emissions and fuel economy (H95 head, 1981-1982 USA all engines)
-
- Regular oval (28 mm x 34 mm). These std A14/A15 ports are best for high-RPM operation, or for the bigger engines
-
- NOTE: the top of the port comes up to the centerline of the top bolts
-
- Large oval (GX and A12T, 30 mm x 36 mm). From A12GX Engine and B210 or Cherry A12T engines.
-
- NOTE: the top of the port comes up as high as the top of the top bolt holes (port comes up past the bolt hole centerline)
-
GX Oval vs. A14 Oval Comparo
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.
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
| Ports | Size (mm) | Exhaust | Raised | Note |
| round | 28 | 27x26 | no | 1971 A12 |
| round | 28 | ? | lowered | 1977 GFU |
| Oval - Small | 28x30 | ? | no | 1973 A13 |
| Oval - Medium | 28x32 | 28x26 | no | A14E, A15E |
| Oval - Regular | 28x34 | 28x26 | no | Many A14s |
| Oval - Large (GX) | 30x35 - 36 | 27x29 or 28x26 | Yes | A12GX (1971-1973) |
- GX extra-large oval ports (36 mm tall)
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
Intake/Exhaust manifold bolt pattern
The 1971-1973 A12 differs from the A13/A14/A15 and some A12s after 1973. A12 Wagons and Trucks continue to use the old pattern for some time
Top: New bolt pattern
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.
Bolt pattern
Valve Springs
The following A-series heads had dual valve springs. There is a small-diameter spring inside the main spring.
- A12GX
- early A12T
- late A12T
- A14T
- A14E, A15E
- Heads retro-fitted with dual springs
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
| Valves | Intake PN (13201) | In. Size | Exhaust PN (13202) | Ex. Size | Length |
| A10, early A12, late A12 Van | 13201-H1000 | 35mm | 13202-18000 | 29mm | 103.8 |
| A12GX/A12T | 13201-H2300 | 35mm | 13202-H2300 | 29mm | 103.8 |
| Late A12, A13, A12AS | 13201-H2300 | 35mm | 13202-H7400 | 29mm | 103.8 |
| A13(1974),A14 & A15 | 13201-H6200 | 37mm | 13202-H6200, H8900 | 30mm | 103.8 |
| A12A, A14, A15 1981-82 USA | 13201-H9500 | 35mm | 13202-H9500 | 30mm | 100.0 |
| A12A, A14, A15 1981-82 canada | 13201-H6200 | 37mm | 13202-H6200 | 30mm | 103.8 |
Nissan Competition
VALVES (A-SERIES)
4 of each required * 13201-H2300 35MM/1.38" INTAKE VALVE A12, A12GX * 13201-H6200 37MM/1.46" INTAKE VALVE A14, A15 * 99996-H1100 COMPETITION 37MM/1.46" INTAKE VALVE * 13202-H2300 29MM/1.14" EXHAUST VALVE A12, A12GX * 13202-H6200 30MM/1.18" EXHAUST VALVE A14, A15 * 99996-H1110 COMPETITION 30MM/ 1.18" EXHAUST VALVE
Competition Valves are "Polished and tuliped for improved flow characteristics".
Reference: 1984 Nissan Competition Catalog
A12GX Head Identification
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 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):
Datsun Competition heads have raised ports ceilings visible on the top face.
Head Front Face
- 3-bolt original type for left-mount alternator
-
- 4-bolt, adds high right-side high alt mount
-
- 5-bolt, adds right-side low alt mount
-
- 5-bolt with Air Pump air passage
-
A14T
H72 head
Adapter
Spark-side Bosses
Look at the accessory/bracket mounting holes.
No bosses
One boss (undrilled, 1973?):
One boss (drilled, 1973?):
Three boss (late 1970s):
Manifold-side Bosses
Variations * No boss * Front boss, undrilled * Front boss, drilled * Rear boss only (no front boss) * Rear and Rear bosses
Front Boss location
Various fittings can be inserted: Plugs, switches or valves
album
Rear boss location
No Boss
Without boss, early A14
album
Without boss, 5-bolt face:
album
Undrilled Boss
With boss, not drilled, later B110
album
A14 with front boss undrilled
album
Front Boss Drilled & Tapped
With boss (fitted with vacuum switch in this photo)
album
Late A12
album
Front and Rear Bosses
With rear boss not drilled, front boss drilled
Blank rear boss, tapped front boss
album
With rear boss drilled, front boss undrilled
album
Rear Boss Only
With rear boss (no front boss) H89
album
Alternator Mounting
Also see: Alternator mounting
Left Side: early A-series engine (front distributor)
- B10,B110,E10: on left side of engine, down low
- Upper bracket bolts to front face of head
-
-
Right Side: late A-series engine (mid-distributor)
- B210, some B310: up high.
- Upper bracket bolts to Upper bolt hole on head
-
- Some B310: up low.
- Upper bracket bolts to lower bolt hole on head
-
Rear Face
11041-M0800 early A12T
This head has a factory plug in the heater hose outlet.
One big welch plug
1994 A12S
A12GX Identification
A true A12GX cylinder head has all these features:
- Dual valve springs
- No casting numbers
- Large Oval port 30x34.5mm
- 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 (newer 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)
- Boss on side, between plugs 2 & 3
- SAME valve sizes as standard A12: 29mm exhaust, 35mm intake
- NO bosses on side between plugs 1&2 and 3&4 (that indicates a newer head)