Chevrolet 70 1969 Series, Shop Manual

Page: 686 / 913

E N G IN E 6-15
P IST O N A N D R IN G FITTIN G
General
Pistons must be fitted to cylinder bores by measuring to
assure correct clearance between piston skirt and cylinder
wall. Correct clearance is given in “ Specifications" at end
of this section. Pistons and piston rings are available in
both standard and in oversize dimensions.
W hen installing pistons which were removed at disas­
sembly, the pistons must be assembled on respective con­
necting rods and installed in original pistons in block. Pis­
tons should be stamped with corresponding cylinder n u m ­
ber. On all engines, cylinder number 1 is at front of left
bank and cylinder num ber 2 is at front of right bank, thus
left bank cylinders are numbered from front to rear I, 3.
and 5. Right bank cylinders are numbered front to rear 2.
4, and 6. Refer to Figure 21.
Fitting Pistons in New or
Reconditioned Cylinder Block
1. W hen necessary to select replacement pistons for new
block or for block which does not have a ring-travel
ridge, refer to selection size num ber (fig. 22) stamped
on top of block adjacent cylinder bore. N u m b er is
used to indicate bore size to permit selection of stan­
dard size piston for proper fit. Selection numbers
range from 1 through 7 for production as indicated in
“ Specifications" at end of this section. For service
use, four standard size pistons are available. Size 1
for use in cylinders m arked either 1 or 2: size 3 for
cylinders m arked 3 or 4; and size 5 for cylinders
m arked 5 or 6. Size 7 pistons are also available for
use in size 7 cylinder bores.
2. Oversize pistons are available in oversizes shown in
“ Specifications," at end of this section, and do not
have selection numbers. Cylinders must be rebored
and honed to proper dimensions to provide correct fit
as described below when installing oversize pistons.
C AU TIO N : W henever possible, rem ove crank­
sh aft w h en reboring or honing cylinder bores. If
crankshaft is not rem oved, it must be covered
to keep abrasive a w a y from crankshaft b e a r­
ings. Wash cylinder bores after honing and
w ip e dry before checking piston fit.
3. As piston is fitted to each cylinder, stam p cylinder
num ber on top of piston to assure installation ol pis­
tons on corresponding connecting rod and in proper
cylinder. Refer to Figure 44 for location of numbers
on connecting rod and cap.
P R E P A R IN G C Y L IN D E R B O RES
W H E N R E -R IN G IN G P IS T O N S
Inspect top of cylinder bores for ring travel ridge.
Ridge must be removed completely. If cylinder walls are
glazed, use polishing hone to break glaze. At end of hon­
ing operation allow hone to work free in bore. Do not re­
move while hone is still cutting. Clean cylinder walls with
soap and water and stiff scrub brush, and wipe with clean
cloth or absorbent paper. Apply engine oil to cylinder
walls to prevent rusting.
C H E C K IN G P IS T O N R IN G FIT
Refer to Figures 46 and 47 for type and arrangem ent of
piston rings for each engine model. The flexible steel oil
control rings used on 4 0 1M engines are designed to func­
tion without a gap. and ends of ring butt together firmly
when piston is installed in cylinder.
When overhauling engines, new piston rings should be
installed and the procedures described in following steps
should be followed to assure correct fit of rings in piston
grooves and at cylinder walls.
1. Be sure to use oversize piston rings with oversize pis­
tons. Proceed as directed in step 2. to fit compression
rings in all engines. The same method is used to
check fit of oil control ring for 4 78 1VI engines.
2. Place piston rings, one at a time, in cylinder in which
they are to be used; and push ring at least halfway
down into cylinder bore, using head of piston to posi­
tion the ring squarely in bore. Measure ring gap with
feeler gauge (fig. 22). Each compression ring gap
must be within limits specified in “ Specifications" at
end of this section. If gap is too small, remove ring
and dress off ends of ring with fine cut file or other
tool designed for this purpose.
3. Try fit of each compression ring in respective groove
in piston. Using feeler gauge, measure ring clearance
which must be as specified. Clearance in excess of
specifications indicate worn ring grooves.
4. Keep piston rings with the piston on which they are to
be used. Instructions for installing rings on pistons
are given later in engine build-up instructions.
A SS E M B L Y OF C O N N E C T IN G R O D A N D P IST O N
1. If original pistons and connecting rods are to be in­
stalled, refer to m arks (numbers) on connecting rods
t , , C'-MSHAFT
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Figure 2 3 — R e m o v in g G e a r from C a m s h a f t
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK S H O P M A N U A L