Cylinder Head Identification

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

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

Port Shape

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

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

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)