od of construction won the
flattery of imitation by makers of other nationality.

The cooling system for the cylinders is extremely efficient. After
leaving the water pump, the water enters the top of the front cylinders
and passes successively through each of the six cylinders of the row;
short tubes, welded to the tops of the cylinders, serve as connecting
links in the system. The Panhard car engines for years were fitted with
a similar cooling system, and the White and Poppe lorry engines were
also similarly fitted; the system gives excellent cooling effect where
it is most needed, round the valve chambers and the cylinder heads.

The pistons are built up from two pieces; a dropped forged steel piston
head, from which depend the piston pin bosses, is combined with a
cast-iron skirt, into which the steel head is screwed. Four rings are
fitted, three at the upper and one at the lower end of the piston skirt,
and two lubricating oil grooves are cut in the skirt, in addition to the
ring grooves. Two small rivets retain the steel head on the piston skirt
after it has been screwed into position, and it is also welded at two
points. The coefficient of friction between the cast-iron and steel is
considerably less than that which would exist between two steel parts,
and there is less tendency for the skirt to score the cylinder walls
than would be the case if all steel were used--so noticeable is this
that many makers, after giving steel pistons a trial, discarded them in
favour of cast-iron; the Gnome is an example of this, being originally
fitted with a steel piston carrying a brass ring, discarded in favour of
a cast-iron piston with a percentage of steel in the metal mixture. In
the Le Rhone engine the difficulty is overcome by a cast-iron liner to
the cylinders.

The piston pin of the Mercedes is of chrome nickel steel, and is
retained in the piston by means of a set screw and cotter pin. The
connecting rods, of I section, are very short and rigid, carrying
floating bronze bushes which fit the piston pins at the small end, and
carrying an oil tube on each for conveying oil from the crank pin to the
piston pin.

The crankshaft is of chrome nickel steel, carried on seven bearings.
Holes are drilled through each of the crank pins and main bearings, for
half the diameter of the shaft, and these are plugged with pressed brass
studs. Small holes, drilled through the crank cheeks, serve to convey
lubricant from the main bea