Some interruptions for holiday aside, we're in the middle of swapping the heads.
It was unexpected to find that the Contour and Mondeo pistons are quite different:
The Contour engine piston tops have machined cut outs for the valves – 2 “D” shaped ones for the exhaust valves and one angled trough for the 2 inlet valves. And the centre of the piston heads is raised so that, at top dead centre, it's about 2mm above the top of the block. The Mondeo ones are completely flat and are very slightly above (too small to measure) level with the top of the block at TDC.
On the basis that we're doing this change because the heads are different, I have to say that the heads do look remarkably similar side by side on the bench. I haven't facilities for detailed measurement but the only notable visual difference is in the inlet valves: Mondeo inlet valves faces (the part you see looking at the valve from the piston) are flat with a small aprox 10mm diameter concave zone in the centre; Contour ones are concave over almost the complete area of the face. The exhaust valves of both engines are the same and similar style to the Mondeo inlet valves.
Whether this is of any significance I don't know. Does it suggest that the compression ratio difference is due to the pistons being different?
Any contributions gratefully received.
