Scientific American Supplement, No. 717, September 28, 1889 | Page 3

the
crank shaft bearings heated very considerably, and continued to do so,
rendering the duration of life of the crank shaft a short one; and though
they were never what is termed out of line, the bearings could not be
kept cool without the use of sea water, and occasionally the engines had
to be stopped to cool and smooth up the bearing surfaces, causing
delays, worry, and anxiety, for which the engineer in charge was in no
way responsible. Happily this state of what I might call uncertainties is
being gradually remedied, thanks being largely due to those engineers
who have the skill to suggest improvements and the patience to carry
them out against much opposition.
These improvements in many instances pertain to the engine builder's
duties, and are questions which I think have been treated lightly;
notably that of insufficient bearing surface, and one of the principal
causes of hot bearings, whereby the oil intended for lubrication was
squeezed out, and the metal surfaces brought too close in contact; and
when bearings had a pressure of 200 lb. per square inch, it has been
found that not more than 120 lb. per square inch should be exerted to
keep them cool (this varies according to the material of which the

bearing is composed), without having to use sea water and prevent
them being ground down, and thus getting out of line. I have known a
bearing in a new steamer, in spite of many gallons of oil wasted on it,
wear down one-eighth of an inch in a voyage of only 6,000 miles, from
insufficiency of bearing surface.
Several good rules are in use governing the strength of shafts, which
treat of the diameter of the bearings only and angles of the cranks; and
the engine builder, along with the ship owner, has been chary of
increasing the surfaces by lengthening the bearings; for to do this
means increase of space taken up fore and aft the vessel, besides
additional weight of engine. Engine builders all aim in competing to
put their engines in less space than their rivals, giving same power and
sometimes more. I think, however, this inducement is now more
carefully considered, as it has been found more economical to give
larger bearing surfaces than to have steamers lying in port, refitting a
crank shaft, along with the consequences of heavy bills for salvage and
repairs, also the risk of losing the steamer altogether. Proportioning the
bearings to the weights and strains they have to carry has also been an
improvement. The different bearings of marine engines were usually
made alike in surface, irrespective of the work each had to do, with a
view to economy in construction.
In modern practice the after bearings have more surface than the
forward, except in cases where heavy slide-valve gear has to be
supported, so that the wear down in the whole length of the shaft is
equal, thus avoiding those alternate bending strains at the top and
bottom of the stroke every revolution. Another improvement that has
been successfully introduced, adding to the duration of life of crank
shafts, is the use of white bearing metal, such as Parson's white brass,
on which the shafts run smoothly with less friction and tendency to heat,
so that, along with well proportioned surfaces, a number of crank shafts
in the Peninsular and Oriental Co.'s service have not required lining up
for eight years, and I hope with care may last till new boilers are
required. Large and powerful steamers can be driven full speed from
London to Australia and back without having any water on the bearings,
using oil of only what is considered a moderate price, allowing the

engineer in charge to attend to the economical working of both engines
and boilers (as well as many other engines of all kinds now placed on
board a large mail and passenger steamer), instead of getting many a
drenching with sea water, and worried by close attention to one or two
hot bearings all the watch. Compare these results with the following: In
the same service in 1864, and with no blame to the engineer in charge,
the crank shaft bearings of a screw steamer had to be lined up every
five days at intermediate ports, through insufficient bearing surfaces.
Sea water had continually to be used, resulting in frequent renewal of
crank shaft. Steamers can now run 25,000 miles without having to lift a
bearing, except for examination at the end of the voyage. I would note
here that the form of the bearings on which the shafts work has also
been much improved. They are made more of a solid character, the
metal being more equally disposed round the shaft, and the use of gun
metal for the main bearings