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2 3 1 V6 ENGINE V.I. CODE C
6A3-19
wear of new pistons and rings will result. A satisfactory
method of fitting pistons is as follows:
1. Remove all rings from pistons which will be fitted. It
is not necessary to separate rods from pistons. If an excess
amount of varnish or carbon appears as a ridge at the top of
the cylinder, remove by scraping or sanding.
2. Wipe bores and pistons clean, removing oil or other
foreign material. Select a piston-rod assembly for the bore to
be fitted (or piston and pin if a new piston is being fitted) and
position down into the bore with the top of piston down. See
Fig. 6A3-39. The piston should fall free by its own weight
through the bore when the bottom of the piston skirt is 1/2"
to 1" from top of block. See Fig. 6A3-40. Caution must be
used to insure piston is not damaged when it "falls" through
the cylinder. If it doesn't, the piston fit is too tight and
another piston should be selected until the piston will slide
freely through the bore without any force being applied. Mark
piston and bore for proper assembly.
3. After a piston has been selected, which will slide freely
through a bore, it must be determined if piston fit will be too
loose. This is done by placing a .0025" feeler gage for used
pistons, and a .002" feeler gage for new pistons at least 6"
long and not over 1/2" wide, down into the same bore with
selected piston while holding feeler to top of the bore. See Fig.
6A3-41.
Position selected piston and feeler down into the bore
until the bottom of the skirt is again 1/2" to 1" from top of
block, being sure that the feeler gage is 90 degrees from the
pin. If the piston hangs on the feeler gage and does not fall
free, it indicates that the piston is correctly fitted to that
respective bore. See Fig. 6A3-42 and 6A3-43. Mark both
piston and bore before going to the next bore. If the piston
fell free during this check with the .0025" feeler gage (.002"
feeler gage for new pistons) then that particular piston is too
samall for the bore and a larger diameter piston will be
required.
NOTE: When checking more than one bore, it is very
possible that what may be a piston too small for one bore
will be a correct fit in another. It is very improbable that
any engine will require all 6 or 8 pistons to be changed.
FITTING NEW PISTON RINGS
When new piston rings are installed without reboring
cylinders, the glazed cylinder walls should be slightly dulled,
but without increasing the bore diameter, by means of the
finest grade of stones in a cylinder hone.
New piston rings must be checked for clearance in piston
grooves and for gap in cylinder bores. The cylinder bores and
piston grooves must be clean, dry and free of carbon and
burrs.
With rings installed, check clearance in grooves by
inserting feeler gages between each ring and its lower land
because any wear that occurs forms a step at inner portion
of the lower land.
If the piston grooves have worn to the extent that
relatively high steps exist on the lower lands, the piston
should be replaced because the steps will interfere with the
operation of new rings and the ring clearances will be
excessive. Piston rings are not furnished in oversize widths
to compensate for ring groove wear.
Fig.
6A3-39
Positioning Piston in Bore
Fig.
6A3-40
Piston Fall
Fig.
6A3-4
1
Positioning Feeler Gage
When fitting new rings to new pistons the side clearance
of the compression rings should be .003" to .005" and side
clearance of the oil ring should not exceed .0035".
To check the end gap of compression rings, place the
ring in the cylinder in which it will be used, square it in the
bore by tapping with the lower end of a piston, then measure
gap with feeler gages. Piston rings should not have less than
.010" (compression rings) and .015" (oil ring) gap when
placed in cylinder bores. If gap is less than specified, file the
ends of rings carefully with a smooth file to obtain proper gap.
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