Engine
Machining
Decking the Block
• The deck of the block should not be warped
to insure a sufficient head gasket seal.
• Concurrently, block deck should be parallel
to the main bearing bores.
• Block deck is checked with a straightedge
and a feeler gauge at six different positions,
check manufacturers specifications.
(a) Checking the flatness of the
block deck surface using a
straightedge and a feeler
(thickness) gauge.
(b) To be sure that the top of the
block is flat, check the block
in six places as shown.
Decking the Block
• A block that has been “decked” will have
it’s surface(s) sanded parallel with the crank
bore. Pg.446
– Decking the block will raise static compression.
Cylinder Boring
• Cylinders are usually tapered after extensive
usage.
• Most of the wear will occur at the top of the
cylinder, just under the ridge.
– Though not highly advised, the ridge may be
removed with a “ridge-reamer” for piston
removal.
• The engine must be “bored” and new
pistons fitted if the cylinder is out of
specification.
Courtesy of Dana Corporation, Perfect Circle Products
Most of the cylinder
wear is on the top inch
just below the cylinder
ridge. This wear is due
to the heat and
combustion pressures
that occur when the
piston is near the top
of the cylinder.
Ridge being
removed with one
type of ridge
reamer before the
piston assemblies
are removed from
the engine.
Cylinder Boring
• Maximum bore oversize is determined by
cylinder wall thickness and piston size
availability.
• An ultrasonic test may be performed to
determine cylinder wall thickness.
• Cylinders should be machined to the
smallest oversize possible.
Cylinder Boring
Calculating oversize diameter …
• One method is to factor the maximum
amount of taper, double it, and add .010in.
This will give you your piston size.
Cylinder Boring
• A boring bar is used to bore the cylinder
diameter.
• The cylinder must be perpendicular to the
crank-shaft bore before boring is attempted.
• Main bearing caps must be installed and
torqued to specifications prior to boring.
Cylinder Boring
• Cylinders are bored .002” - .010” under the
finish bore size.
• Torque plates should be used on the deck
for bores larger than .030”. Pg.451
• Boring leaves a finish too rough for service.
After boring, the cylinder surface
is rough and fractured to a depth
of about one thousandth of an
inch (0.001 in.).
Cylinder Honing
• The cylinder finish is, in effect, sanded to a
proper finish and/or size.
• Deglazing hone – removes the hard surface
glaze remaining after normal engine usage.
– A flexible hone that follows the shape of the
cylinder wall.
• Ball type
• Stone type
Cylinder Honing
• Sizing hone – used to finish a bore
procedure, straighten cylinder taper and
provide a suitable surface for the piston
rings.
• While size honing, the cylinder must
constantly be checked with a bore gauge to
check for size and taper.
– Cylinders will generally hone quicker closer to
the deck of the block.
Measure the bore diameter
at the top just below the
ridge and at the bottom
below the ring travel.
Take measurements in line
with the crankshaft and then
repeat the measurement at
right angles to the centerline
of the block in each cylinder.
Dial bore gauge
Sizing hone
Torque plate
An engine being honed. The block
is equipped with a torque plate to
stress the block the same as if the
cylinder head was attached.
TECH
TIP
Cylinder Honing
• While honing, it is important to constantly
move the hone in a vertical motion.
• This vertical motion insures that a
cross-hatch finish is left.
– The crosshatch should be between 20 and 60
degrees.
• Too little crosshatch will cause excessive ring wear.
• Too much may effect compression.
The crosshatch
pattern holds oil and
keeps the rings from
wearing excessively.
Cylinder Honing
• Plateau honing – using different grit stones,
in succession, to achieve proper size and
finish. May be done in two or three steps
(different size stones).
• The grit of the finishing stone will be
determined by the ring composition.
– Chrome - #180 grit
– Cast iron - #200 grit
– Moly – #220 grit
Cylinder Honing
• The top edge of the cylinder should be
chamfered prior to honing.
• Cylinders are finish honed to specific piston
diameters to insure proper clearances.
• The finished hone should be within .0005”
of desired size and taper
Piston diameter
being measured
using a micrometer.
Cylinder Honing
• The cylinder must be thoroughly cleaned
after any honing is done to remove dirt and
abbrasives.
– This is done with a brush, soap and water.
– The cylinder can be wiped with a clean, dry
cloth to check cleanliness of the walls.
Lifter Bore Honing
• Lifter
bores are
deglazed
with a
finishing
stone to
remove
wear
patterns.
Lifter
Bore
Sleeve
Main Bearing Bores
• Final machining of the main bearing bores
(align bore) and cam bearing bores is done
with the main caps torqued.
• FOR THIS REASON, MAIN CAPS ARE
NOT INTERCHANGEABLE NOR
UNIDIRECTIONAL.
Main Bearing Caps
• Designs include …
– A Girdle design. (pg. 440 fig. 19-24).
– A two bolt main cap (pg. 439 fig. 19-21).
– A four bolt main cap (pg. 439 fig. 19-22).
• Mostly high-performance and truck
designs.
Girdle-type Cap
Main Bearing Caps
– A six bolt main cap design. (pg. 440
fig.19-43)
– A bedplate design (pg. 435 fig. 1910).
• Attaches to the bottom of the
block and supports the crankshaft.
Bed Plate
Main Bearing Caps
• The main bearings are held into
place by the main bolts and
enlarged areas of the block called
bosses.
Main Bearing Bores
• M.B.B.s may elongate over time and
become egg-shaped (pg. 441 fig. 19.27).
– This out-of-round can be checked with a bore
gauge in 3 different positions. 0.0005 variance
is considered acceptable.
• The main bearing bore not contained within
the cap is called the saddle.
– The saddle will be part of the engine block in
most cases.
Main Bearing Bores
• If the M.B.B. is measure outside of
limits, the saddles can be checked with
a straightedge and feeler gauge (pg.
441 fig. 19-28).
• If the saddles are within limits, the face
of the caps may be block sanded to
compensate for out-of-round.
The main bearing bores of a
warped block usually bend
into a bowed shape.
The greatest distortion usually
occurs in the center bores.
Main Bearing Bores
• The main bearing bores must then be
align honed to restore its symmetry.
(pg 458 sequence).
– Note: the depth of the saddle cannot be
altered because this will alter the
centerline distances between the crank
and cam.
Cylinder Sleeves
• Cast iron or steel sleeves
are installed at the factory
on some aluminum engine
blocks.
– They may be cast or pressed
into the block.
• Silicon-aluminum blocks
have no sleeves installed.
– Pistons with zinc-copperhard iron coatings are used
in this design (Porsche
944).
Cylinder Sleeves
• A dry sleeve is completely supported by the
engine block and does not come in direct
contact with the coolant passages (Saturn,
Ford, Northstar (pg. 434)).
• A wet sleeve is in direct contact with the
water passages. Therefore, they must be
thicker to withstand combustion pressures
(Cadillac 4.1, 4.5, 4.9).
Cylinder Sleeves
• A sleeve may be installed into a cast iron
block if a cylinder is badly damaged.
– Typically, the cylinder is bored to the exact
outside diameter of the sleeve. A ridge is left at
the bottom of the cyl. To support the sleeve.
• The block is then heated and the sleeve
frozen to aid installation.
Crankshaft Grind
• The crankshaft must be ground if not within
specification
– Generally speaking, if the groves on the crank
journal can be felt with your finger-nail, it
should be ground