Cylinder heads

[Jota Rob]

Just comparing 2 skull heads with the idea of transposing my porting to the new head.

Now I discover that the spark plug hole is in a different location where it enters the combustion chamber.

The angle at which it's drilled ( from the factory, 14mm plug hole) is different. Meaning it's too close to a big inlet valve.

Is this a known aspect of big valve heads? 81 vs 79.
Bit of a downer.

 

[sfcpiet]

Rob,

The 120° engines recieved a very different head, not only in regard to casting execution and quality. The sparkplug angle was changed, along with combustion chamber depth. The shallower chamber (ca. -0.5mm) necessitated the use of 0.5mm shorter conrods to keep CR within the ball park.

The different plug angle can be recognised by the slight scallops in the edges of the top deck of the head to allow a regular tube spanner to be used for plug fitment. The same heads were also used for the later RGS Corsa and SFC1000 with their 40.5mm inlet valves. Because the actual cast iron skull is slightly more substantial (to accomodate seperate valve seat inserts) than the earlier type, cracks between plug hole and seats are rather uncommon.

I'm not aware of any major changes made prior to the 120° introduction.

piet

 

[Jota Rob]

Cheers Piet.

Interesting evolution.

I took some pics from the other side and saw this difference.
I'll have to work with plan B, the original head.
Rob