A little detailed info on BMW cylinders.

The Nicasil cylinders are finished with a plating process, if the block is bored and/or honed, the plating process must be re-done.

The Alusil cylinders are acid etched, this removes the aluminum from the silicon particles on the bore surface (the piston rings ride on the silicon surface). If the block is bored and/or honed, the acid etching process must be re-done.

The Nicasil blocks do not have a high enough silicon content to allow for an acid-etch process.

The Alusil block can be Nicasil plated, but the etching process is more cost effective.

Any sulfer in the fuel, combined with low operating temps (lots of short trip driving) causes sulfuric acid production, stripping the Nicasil coating.

__________________
'03 X5 4.4 Sport, last of the M62s (8-03 build date)
I believe in deadication to craftmanship in a world of mediocrity!