Machining also smooths the surfaces of engine parts by wiping away
scoring or other blemishes to allow gaps between the engine and its
moving parts, and also makes these gaps a consistent measurement. In
this case, the machine work undertaken on a 331-cid overhead-valve V-8
from a 1955 Cadillac will bring the engine back to factory specifications
as closely as possible. This engine will receive new pistons, crank
bearings and camshaft bearings, and a rebuild will be undertaken on the
heads to make them compatible with unleaded fuel.
Boring the block
To make an engine’s internal surfaces even, square and smooth,
material from the engine must be removed in the machining process.
Since engines have tight tolerances for space between parts, the material
that is removed to make a surface flush must be replaced to maintain an
engine’s correct specifications, whether it’s with oversized bearings or
pistons. If not, the parts will move and shift within the engine and it will
be destroyed.
For this Cadillac 331-cid V-8, the machining started with the crank,
because any work on the crank affected the size of other parts,
particularly the crank bearings. After its removal, the crank was
inspected by Troy Herman, an employee of Metal Crafters in Stevens
Point, Wis., where the engine rebuild was undertaken.
Herman began by measuring the diameter of the crank and comparing
it to the diameter stated in the 1955 Cadillac shop manual to determine
if the diameter had reduced through years and miles of spinning. While
the diameter of the crank checked out to factory specifications, small
grooves were found where the crank rode in the bearings. This meant
the crank needed to be turned until the surface was smooth. This work
was sent to another shop that specializes in turning crank shafts, and
after the shop reported that it machined off .010 inches from the
surfaces of the crank that ride in the bearing, Herman ordered oversized
crank bearings. Oversize bearings were necessary because the crank of
an engine spins along insert bearings that are placed between a saddle in
the block, forming the top half of a perfectly round cradle for the crank,
and the crank caps, which are the bottom of the cradle. With some
surface material removed from the crank to smooth out the area in