Diesel Engine Cylinder Blocks

Diesel Engine Cylinder Blocks
Cylinder Block Design
The cylinder block can be described as the largest
single part and the main structure, or "backbone," of
the diesel engine. It’s primary function is to support
cylinders and liners as well as major engine
components such as the crankshaft and camshaft.
All other engine parts are bolted or connected to the
cylinder block in some way. For this reason block
design must be configured to perform these
functions well having maximum durability under
extreme operating conditions.
piston and rod. Secondary balance is when the
movement of one piston balances the movement of
another. V6's have a secondary imbalance that causes
engine vibration. This inherent balance that translates
into improved smoothness, reliability and fuel
economy.
On major drawback to inline 6’s is the length of the
engine. The length of the engine allows more harmful
torsional twist in the crankshaft, and makes cooling
all the cylinders evenly more difficult. Stiffening the
crankshaft helped reduce torsional twisting.
Dampening harmonic vibration is critical.
Blocks must be designed as compact as possible to
reduce weight and size. Adding ribs and webbing to a
diesel engine block not only adds life extending
rigidity but minimizes engine noise and vibration.
Serpentine blocks or reinforcing plates such as used
by Caterpillar enhance these characteristics.
Below Volvo VED-12
Above: Navistar HT 530 HEUI
Most engine blocks are inline or “V” banked. Inline
engines are preferred in heavy-duty diesel engines
since the crankshaft is supported by more main
bearings. An inline six is also among the bestbalanced layouts for the internal combustion engine
- inherently taking advantage of the power and
compression strokes to balance out opposing forces
at work within the engine block during the
cylinders' firing order. Inline 6’s have both primary
and secondary balance. Primary balance is when the
crankshaft counterweights offset the weight of the
Most engine blocks are manufactured from cast
iron.
The advantage of cast iron is it provides ease of
machining, manufacturing, corrosion resistance and
absorbs vibration. To improve strength, hardness
and corrosion resistance, manufacturers may add
nickel, molybdenum and chromium alloys. Cast
iron is still not as strong as steel therefore machine
threads are often coarse threads pitch to minimize
the problem of “stripping” or pulling out threads.
Casting of blocks requires the removal of sand from
inner passageways. Core plugs – sometimes called
frost plugs are used to cover holes made in the
block to flush sand out of small passageways. After
rough casting blocks tend to warp and are stored or
heat-treated to “season” them. Hardening processes
take place during this time and heating the block
tends to speed up the process. Subsequent to this,
castings are bored, tapped and machined to finish.
Types Of Diesel Engine Blocks
No- Sleeve Block
A parent-bare or no-sleeve block has holes bored
for the cylinder with the pistons and piston rings
inserted directly into this hole. No provision in the
block for or dry-type sleeves is made.
Advantages
¾ The major advantage is the initial cost of
construction in that the machining and fitting of
sleeves is not required.
¾ No provision has to be made for O-ring grooves
and no contact area is needed.
¾ The block can be made lighter because of thin
cylinder wall construction.
Disadvantages
¾ A major disadvantage of this type of block is that
during rebuild or repair of the engine a worn cylinder
must be re-bored or honed.
¾ Reboring requires special equipment and the
engine must be disassembled completely
¾ Reduced engine block life. Since cylinder walls are
irregularly thick, heat transfer differentials cause
varying cylinder dimensions and accelerated wear.
Wet Sleeve
A wet sleeve or liner block is designed with a number
of large holes into which the cylinder sleeves are
inserted. These holes are designed so that the coolant
will be circulated around the cylinder sleeve or liner
The coolant is prevented from leaking into the
crankcase of the engine most often by O-ring seals at
the bottom of the liner At the top of the block a
counter-bore may be cut into the block for the lip or
flange of the sleeve to fit onto and prevent coolant
leakage. The uppermost part of this lip may be
slightly larger than the counter-bore to provide a
sealing interference fit.
Advantagcs
¾ The major advantage is the contact of coolant
directly with the sleeve, enabling rapid and positive
heat transfer from the combustion chamber to the
coolant.
¾ Sleeves are easily removed and installed during
engine rebuilding to restore the engine to original
specifications.
¾ Cylinder sleeves may be replaced individually if
they become worn or damaged prematurely
Disadvantages
¾ The major disadvantages are the problems
encountered in maintaining a coolant seal between the
bottom of the sleeve and the block. The seals used (O-
ring and crevice seals) often do not have the same
longevity as might be expected from the engine.
¾ This seal leakage generally occurs at the bottorn
of the sleeve and contaminates the lube oil.
¾ Additional and careful maintenance of the
cooling system is required in wet sleeve engines to
prevent cavitation.
Cavitation
Since diesel engines have long strokes and a sharp
increase in combustion chamber pressures they
experience a unique problem from pitting of
cylinder liners from the outside in. This condition
known as cavitation is caused by the implosion of
vapour bubbles into the liner.. As the liner vibrates
and flexes due to combustion forces (or is bulged
by the side thrust of the piston against the cylinder
wall) vapour bubbles form along the outside of the
liner in the region where the liner moves out and
back the most. Negative or low pressures enhance
the formation of the bubbles much like liquids boil
out of an A/C system during evacuation. After the
bubbles form and pressure is normalized again the
bubbles implode or collapse with explosive force
against the cylinder wall. This phenomenon is
something like the sound heard when a pot is
heating on a stove. Loud popping sounds are heard as
hot steam vapour rises into cooler water and
collapses. All diesel engines are afflicted by this
phenomenon however engines with thinner more
flexible liners have the greatest problems.
Dry Sleeve Block
A dry sleeve. block is designed with a bored or honed
hole in the block that allows no coolant contact with
the cylinder sleeve, The sleeve is inserted into the
bored hole or it can be either a "slip or press fit." A
counter-bore is bored into the block to accommodate
the liner flange.
Advantages
¾ The dry sleeve type does not have coolant in
contact with the cylinder sleeve, since the sleeve is
fitted into a bored hole in the block. This is a major
advantage in that sealing the sleeve at the bottom is
not required.
¾ There is no lube oil contamination as a result of the
leaking of coolant by the sleeve seals.
¾ The block can be brought back to like~new
condition easily by the installation of new sleeves.
¾ Cylinder sleeves may be replaced individually if
they become worn prematurely or damaged.
Disadvantages-Dry Sleeve
¾ Since the coolant is not in direct contact with the
sleeve, heat transfer from the combustion chamber
to the coolant water is not as rapid as it would be
with a wet-type sleeve.
¾ This slow heat transfer may result in short engine
life and cylinder damage.
¾ Extra machining and weight as with a wet
sleeved engine add to the expense of manufacturing
Below: 2-Stroke Dry Liner Counter bore
Cylinder Liners & Sleeves
The cylinder liners (or sleeves) are basically
“replaceable cylinders walls" which are used to
restore the engine cylinders to their original
condition.
Cylinder Liner/Sleeve Problems:
Liner-to-Cylinder Block fit -The fit of a liner
to the cylinder block plays an important role in how
well or how poorly other components (such as
pistons and rings) wear in the course of an engine
lifetime. A liner with an excessively loose fit will
not transfer heat within the cylinder to the block as
effectively as a liner with the correct fit. Heat not
transferred then becomes heat build-up, which can
cause scuffing, scoring and, eventually, seizure of
the piston. An excessively tight-fitting liner
(exceeding specifications) will collapse and distort,
reducing the piston-to-liner clearance, causing hot
spots. Consequently, the piston and liner can
become scored, which could lead to eventual
failure.
Piston-to-liner/sleeve fit - Sufficient skirt
clearance must be maintained between the liner or
sleeve and the piston to allow for normal expansion
of the piston when running at operating
temperature.
Insufficient skirt clearance will reduce the running
clearance and could lead to scuffing or scoring.
Excessive clearance will result in piston knock or
slap
Flange Breakage - Flange breakage is usually
caused by excessive flange loading because of
excessive pressure that was used on the flange when
installing the liner. Flange breakage can result from
any/all of the following:
•Improper torquing of cylinder head after rebuild.
•Unequal flange height above deck
•Uneven wear in cylinder block flange counterbore,
not uniform in depth, or out of parallel to the top
surface of the block
•Worn inner edge of flange counterbore seat (in
cylinder block), causing seat to tilt downward
•Improper positioning of fire ring
Liner counterbores can be repaired by cutting and
machining the counterbores.
A liner with
inadequate protrusion can be raised with the
installation of a shim beneath the liner flange.
Liner Damage
From Valve
Contact – Due to
Worn Valve
Guides
Above: Counter-Bore Problems
Liner protrusion should be measured after installing
and clamping the liner in the block. Very little
variation between liner heights is acceptable and
even less variation in height around the
circumference.
Liner &
Counterbore
Shim
Above: Dial Indicator & Sled Used to
Measure Liner Protrusion.
Above: Liners should be clamped in place
and measure at 4 points to detect variation
Mid-Stop/Wet-Dry Liners
Since wet type liners with an interference ft
between the flange and counter bore are prone to
problems, new liner designs have emerged in the
1990’s. These include Mid-Stop or Wet /Dry
Liners.
The advantage of these liners are several. First, the
counter bore is half way or mid way down the liner.
The ledge or counter bore is much stronger in this
region. Using a ledge in this area eliminates the
need for a “O” ring to seal coolant. The possibility
of breaking the liner instead of a flange is greatly
minimized. Secondly, these liners are used to
minimize engine block weight by requiring smaller
limited cooling jackets.
Above: Cat 3176 Liner
Cylinder Reconditioning
Cylinder walls have the greatest amount of near
the top at the end of compression ring travel. This
tendency for the cylinder to wear into a taper is due
to:
• Higher cylinder pressures near the top part of
piston travel which increases ring unit loading of
the cylinder walls. (Gas pressure behind the rings is
greatest there).
•Higher cylinder temperatures which make the
cylinder wall “softer”.
•Lack of upper cylinder wall lubricant.
Above: Cylinder ridge removal to prevent
ring damage
To measure the amount of cylinder taper within a
cylinder several methods can be used. One is to
measure the amount of piston ring end-gap in a
The ridge that is formed from carbon deposits and
“untravelled” cylinder wall surface above the top
ring will leave a ridge which must be removed prior
to piston removal if ring and piston damage is to be
prevented.
Due to the thrust angle of the piston against the
cylinder wall near BDC, the cylinder may develop a
bell like shape near the bottom.
cylinder after “squaring” the ring inside the cylinder
with a piston. By measuring the end gap at the top
– near the ring turn around area, the middle and
bottom, cylinder taper can be calculated.
Cylinders can also be measured using dial
bore gauges. - Below
• Highly polished liners will not allow residual oil to
cling to the cylinder walls causing scuffing and piston
wear.
• Highly polished liners indicate worn cylinders. Lack
of a crosshatch will prevent oil from clinging to
provide lubricant for the piston. Scuffing and wear
results
Cylinder crosshatch is produced when an engine is
manufactured and during reconditioning
Above: Cylinder Cross Hatch
Above: Microscopic Finish on Cylinder walls
to retain oil and assist ring seating.
In order to reduce the time for engine break-in,
manufacturers use a process called “plateau honing”.
This involves limiting the depth of the cross hatch
with the use of specialized cylinder tools.
The presence of crosshatch on the cylinder wall is
important to provide a surface to seat piston rings
and to retain oil for piston and ring lubrication.
Above: Crosshatch is produced by moving
the hone through the cylinder at a rate of
2 strokes per second. Lubricant may or
may not be used.
Above: Brushes Used to Produce Plateau
Honing
Plateau honing reduces break-in time and oil
consumption during break-in.
Above: Ball hone used for cylinder cleanup.