chevrolet truck Light Duty Truck 1994 Series Repair Manual Download

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Figure 33— Checking the Cylinder Bore

• If the engine is at high hours or miles, and cylinder

bore wear is past specifications in all or most cylin
ders, then consider reworking all bores to the ser

vice oversize.

• If the engine is at relatively low hours or miles and

the bore distress is limited to one or two bores,
then the distressed bores are the only ones that

need to be reworked.

• Fine vertical scratches will not by them selves

cause excessive oil consumption. Therefore honing
to remove them is unnecessary.

• Note if the cylinder block has the letters J or K

stamped  on  the  pan  rails.  These  letters  refer  to  the
cylinder  above  each  letter,  and  identify  what  grade
size  piston  goes  into  that  bore  during  the  produc
tion  process  to  ensure  precise  piston  to  bore  clear
ance.

• If a significant area of the bore is polished through

the hone marks, but otherwise serviceable, break
the polished surface lightly with a finish hone and

install new rings. Refer to “ Finish Honing.”

• The pistons should be inspected for cracks, scuff

ing, heavy or deep scratching, ring groove damage,
or other signs of excessive wear.

• Since different grade size pistons may be used in

the same engine, it is important to mark pistons in

reference to their bores.

• Use the smallest possible oversize service pistons

when reconditioning.

• All service oversize pistons are of the same weight

as the production pistons, therefore engine balance
is not affected by using service oversized pistons.

• If honing is not required, prepare the cylinder bores

for reuse by cleaning with a hot water and deter

gent wash. Apply clean engine oil to the bore after

cleaning.

• If boring and honing is required Refer to “ Boring”

or “ Honing.”

The following is general information on the subject of

boring and honing. A detailed description of types of
equipment, speeds, feeds, grid sizes of honing stones,

cycle times, etc. is beyond the scope of this manual.

BORING

• The boring operation is done with a single point

tool  that  leaves  tool  marks  similar  to  those  found
on  a  phonograph  record.  The  speed  and  feed  of
the  boring  tool  should  be  controlled  to  minimize  the

depth of these tool marks.

• In general, the boring operation imparts the founda

tion for the proper bore diameter, taper and round

ness and the rough honing operation removes the
boring tool marks. Refer to “ Rough Honing.”

• Completely disassemble and clean the block prior

to boring.

• Refer to “ Service Piston Specifications” for selec

tion of service replacement pistons and corre

sponding bore diameters.

• The pistons to be installed should be on hand and

marked  as  to  bore  locations.  Install  reused  pistons
in  their  original  bore  locations.  If  the  bore  has  not
been  re-honed,  then  the  original  rings  with  low
hours  or  miles  may  be  reinstalled  on  the  original
pistons  in  the  original  locations.  If  the  bores  are
re-honed  all  new  ring  sets  should  be  used.

• Before using any type of boring bar, the top of the

cylinder block should be “ stoned” using a flat stone
to remove any dirt or burrs. This is very important.

If not checked, the boring bar may be tilted which

would result in the rebored cylinder wall not being
a right angle to the crankshaft.

• Carefully follow the instructions furnished by the

manufacturer of the equipment being used.

• When reboring cylinders, all crankshaft bearing

caps must be in place and tightened to the proper
torque specifications to avoid distortion of bores in

the final assembly.

• When taking the final cut with a boring bar, leave

approximately 0.13 mm (0.0050 inches) on the
diameter for rough and finishing honing.

ROUGH HONING

• Honing stones are most often spring loaded and

therefore  tend  to  introduce  local  out  of  specification
diameter,  taper  and  roundness  conditions  quickly.
Therefore  it  is  important  to  minimize  the  amount  of
time  required  for  the  rough  honing  operation.

chevrolet truck Light Duty Truck 1994 Series, Repair Manual

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