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| <br>One big welch plug | <br>One big welch plug | ||
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| - | + | <br>1994 A12S | |
| = A12GX Identification = | = A12GX Identification = | ||
Revision as of 07:48, 3 November 2009
At first glance, all A-series cylinder heads look alike. But by careful notice of specific features you can identify the model.
Contents |
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
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.
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.
Sizes:
- ?
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
Head Front Face
- 3-bolt
-
- 4-bolt, adds high alt mount
- 4-bolt, adds high alt mount, with air passage
- 5-bolt, adds low alt mount
-
A14T 
H72 head
-
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
- Without boss, early B110
-
- With boss, not drilled, later B110
-
- With boss, drilled
-
X++
- Without boss
- 5-bolt face:
- With boss, not drilled, front boss drilled
-
- With boss, drilled, front boss undrilled
-
- With boss, drilled, no front boss
-
Alternator Mounting
Left Side
- B10,B110: on left side of engine, down low
- Upper bracket bolts to front face of head
Right Side
- B210: up high.
- Upper bracket bolts to Upper bolt hole on head
- 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)