Vale timing and clearances - symptoms

[Demetris]

repeated clearance comparison tests between the engine at stone stone cold, and after completing multiple 100-mile motorway trips - that the valve clearance in a P6 four-cylinder GROWS by almost precisely 1 thou, for both inlet and exhaust across all cylinders. To my mind, this indicates that the thermal expansion coefficient of the cast-iron camshaft carrier is greater than that of the valve/shim/bucket assemblies by a difference of +0.001 thou, to the extent that additional clearance is generated. Precisely why the exhausts don't appear to grow by a greater degree than the inlets left me a bit flummoxed, but my initial thoughts were that the valve seat grows to offset the relative growth of the exhaust valve. Or something like that. That's pure speculation, but an interesting point of discussion....

Michael, the conditions under which you made measurements with the engine "hot", after you stopped, opened the bonnet, removed the camshaft cover, etc, have not much in common with the situation when the engine runs at speed, the inlet valves are continuously cooled by the incoming air and fuel, while the exhaust ones are bathed in flames and exhaust gasses.
There's no comparison really.