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151 ENGINE
6A2-2 1
Fig.
6A2-48
Normal Cylinder Wear Pattern
Fig.
6A2-49
Measuring Cylinder Gage
When honing to eliminate taper in the cylinder ful
1
strokes of the hone in the cylinder should be madein addition
to checking measurement at top, middle and bottom of bore
repeatedly.
When boring, always be sure the crankshaft is out of the
way of the boring cutter when boring each cylinder:
Crankshaft bearings and other internal parts must be covered
or taped to protect them during boring or honing operation.
When taking the final cut with a boring bar, leave .001" on
the diameter for finish honing to give the required piston to
cylinder clearance specifications. (Honing
or boring
operation must be done carefully so that specified clearance
between pistons, rings, and cylinder bores is maintained).
NOTE: Honing finish should not exceed 7 to 15 micro.
By measuring the piston to be installed at the sizing
points (Fig. 6A2-50) and adding the mean of the clearance
specification, the finish hone cylinder measurement can be
determined. It is important that both the block and piston
be measured at normal room temperature.
SIZING POINT
Fig.
6A2-50
Piston Sizing Points
After final honing and before the piston is checked for
fit each cylinder bore must be thoroughly cleaned. Use soapy
water solution and wipe dry to remove all traces of abrasive.
If all traces of abrasive are not removed, rapid wear of new
rings and piston will result.
Intermixing different size pistons has no effect on engine
balance as all pistons from standard size, up to .03OV oversize,
weigh exactly the same.
PISTON
Fit and Replace
Pistons should be fitted in the bores by actually
measuring the fit (measure
O.D.
of piston at sizing point and
I.D. of cylinder bore). See engine specifications for
clearances. If cylinder bores have been reconditioned, or if
pistons are being replaced, reconditioning of bores and fitting
of pistons should be closely coordinated.
If bore has been honed, it should be washed thoroughly
with hot, soapy water and a stiff bristle brush.
Using a cylinder checking gage, measure the cylinder
bore crosswise of the block to find the smallest diameter.
Record the smallest diameter of each bore.
C AUTI 0 N: When measuring cylinder bores and
pistons, it is very important that the block and
pistons
be
at room temperature. I f any or all of the
parts are hotter or colder than nonnal room
temperature, improper fiting will result.
Measure the piston skirt perpendicular to the
piston pin boss (piston pin removed) and at the
sizing point indicated in
F i g .
6AZ-51.
Make sure the micrometer is in full contact.
As the pistons are measured they should be marked for
size identification and the measurements recorded.
If there is excessive clearance between a cylinder bore
and the piston which was installed in that bore, a new piston
should be used.
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