David Billington wrote:

..A lot of earlier VW beetle crankcases are magnsium.

So for a time were the gearboxes of Bristol engined buses!
After a fire when one was on a milling machine in the factory, extra
flood coolant was installed,
and special fire-fighting equipment around the machine shop.

From then on, all Bristol-engined buses and lorries with the magnesium
boxes were identified externally by different
- hexagonal - wheel hub centres - just so that fire crews etc could
idenify them in an accident.

Dave.

Bristol, UK