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ENGINE: CYLINDER BLOCK AND CRANKCASE
31
Reboring Cylinder Barrels.
After clamping the crankcase to the boring
machine table, insert the machine spindle head
with centering device in a cylinder bore (fig. 31).
Fig. 28 • Using dial Indicator to measure cylinder bores.
1. Olal Indicator. - 2. Zero setting Indicator with master gauge A. 95647'
The measurement of cylinder bore must be
taken both lengthwise and crosswise at two heights
(fig. 21).
Set the dial indicator at zero using the
master gauge A. 95647 (fig. 28).
If
barrel wear or out-of-rOWld are such as recon-
ditioning is required, proceed as follows:
- in case little stock must be removed (less
than
.006" - 0.15 nun), honing
will
do;
- in case stock removal exceeds .006" (0.15 rom),
cylinders must be rebored.
Recall that raboring must not go beyond .0236"
(0.6 nun).
Honing and reboring should be made to cor-
respond to piston oversizes (.0019" - .0157" - .0236",
0.2· 0.4 - 0.6 rom) and to the recommended piston
clearance of .0008" to .0016" (0.020 to 0.040 nun).
Fig. 27 - Diagram for measuring cylinder bores.
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First· 2& - Second - Misurazlone _ Measurement
Honing Cylinder Barrels.
As shown in fig. 29, letters are stamped on the
lower face of crankcase to indicate the bore size.
As a matter of fact, cylinders are graded into
classes on the ground of the bore diameter (2.5590"
to 2.5610" - 65.000 to 65.050 nun) with a .004"
(0.01 nun) progression.
Standard pistons, like cylinders, are divided into
classes so that each cylinder and piston should
belong to the same class.
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Gauge the cylinder bores to determine the
diameter to which barrels should be lapped.
Clamp the cylinder block to the hone table.
Lap barrels first with a set of medium-grain
stones, then using very fine-grain stones.
For better smoothness of barrels
I
polish them
with extremely refined emery cloth wrapped around
hone head.
Fig. 29 - Letters showing cylinder bore classes on lower face
Repeat lapping operation at remaining cylinders.
of cylinder block.
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