(8) Remove six cap screws in main bearing plate at
take-off end of engine. Pry plate off and remove crankshaft
from that end of crankcase (figure 4-17).
(9) Remove cylinder blocks.
Remove all valve
tappets and withdraw camshaft from crankcase (figure 4-18).
Remove three screws and lock washers and then pry gear off
end of camshaft.
Inspection and Repair.
(1) Cylinder Blocks. If cylinders are worn more than
0.005 inch over size they should be reground and fitted with
oversize pistons and rings. Valve stems have a clearance of
0.0025 to 0.0045 inch in the valve guides. If clearance is 0.008
inch drive out valve guides and replace.
Figure 4-18. Removing Camshaft
(1) Install camshaft gear on camshaft using three
screws and lock washers. The gear has offset mounting holes
to provide accurate assembly for valve timing. The gear can
only be put on the correct way for matching the timing mark
PISTON, RING AND ROD CLEARANCES CHART
PISTON TO CYLINDER
.0052 to .0062"
AT PISTON SKIRT THRUST FACES
PISTON RING COMPRESSED GAP
.025 to .035"
Figure 4-17. Removing Crankshaft
.002 to .004'
.0015 to .0035"
(2) Valves. The valve face is ground at 45 degrees
3rd, 4th Groove
.001 to .003"
to the vertical centerline of the valve stem and the valve seat
insert should also be ground at a 45 degree angle. After
CONNECTING ROD TO CRANK PIN -
.008 to .015"
grinding, lap valves and inserts with lapping compound to
prevent improper seating. Clean valve seats and apply lapping
CONNECTING ROD SHELL BEARING
.0015 to .003
compound to valve face and put valves back into guides. Lap
TO CRANK PIN
valves by rotating them back and forth with a reciprocating
PISTON PIN - TO PISTON
.0000 to .0003"
advancing valve tool. Occasionally lift valves and reseat them
.0002 to .0007"
in a different position to insure a uniform seat entirely around
the valve. After lapping, remove valves and wash them and
cylinder block thoroughly with gasoline or kerosene.
(3) Pistons and Connecting Rods. When replacing
shell bearings, replace a complete bearing (2 halves). The
piston skirt is cam-ground to an elliptical contour. Clearance
between piston and cylinder must be measured at the center of
the thrust face of the piston skirt. Refer to figure 4-19 for
proper clearance. The thrust faces on piston skirt are 90
degrees from axis of piston pin hole.
(4) Inspect clearances of parts as indicated in figure
Figure 4-19. Clearances