Makita PM7650H Technical Information page 23

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epair
[4] DISASSEMBLY/ASSEMBLY
[4]-15. Engine block (cont.)
ASSEMBLING ENGINE BLOCK
(1) Connect Piston with Crankshaft complete by inserting Piston pin into place; there is no front/back to Piston.
Note: Be sure to apply a little amount of Makita grease N No.2 to Needle roller bearing.
(2) Secure Piston pin by mounting Ring spring 12 onto each end of Piston pin.
Note: The ring gap of Ring spring 12 can be positioned at any angle to Piston pin.
(3) Install Oil ring in the grooves of Piston; Side rail first, Spacer next, then the other Side rail.
Important: Be sure to fit the three rings with the ring gaps at 120 degrees to one another as shown in the left of Fig. 72.
(4) Install Second ring first then Top ring in the groove of Piston.
Important 1: Be sure to fit the two rings with the ring gaps at 180 degrees to each other as shown in the right of Fig. 72.
Important 2: Second ring has a taper face and must be installed with the large diameter facing Oil ring. (Fig. 73)
Distinguishing between Top ring and Second ring & Discriminating the larger diameter of Second ring:
If both of the two rings are new and unused,
• You can distinguish from their appearances; there is a white marking on the side face of Second ring as shown in
Fig. 74 while not on the side face of Top ring.
• You can face the large diameter of Second ring by placing Second ring with the white marking on your right and
with the ring gap near you as shown in Fig. 74.
If both of the two rings are used and the white marking of Second ring is rubbed off, carefully press the side face of
the two rings to the inner wall surface of Cylinder. You will be able to distinguish the two rings or to discriminate the
large diameter of Second ring through the differences in contact feelings that the different side faces make.
Fig. 72
Side rail
Spacer
Side rail
ring gap
Fig. 73
Top ring, with barrel face
Second ring, with taper face
Side rail
Spacer
Side rail
(4) Apply 4-cycle engine oil to the following portions:
Oil ring, Needle roller bearing that holds Piston pin,
Needle roller bearing of Crankshaft complete.
(5) Remove oil/grease from the mating surface of
Cylinder block and Crankcase.
Then apply ThreeBond to the mating surface of
Crankcase as shown in Fig. 75.
Apply 4-cycle engine oil to the cylinder portion
of Cylinder block, and then while compressing
Piston rings, mount Cylinder block onto Crankcase.
(6) Tighten six M6x30 Hex socket head bolts
in a crisscross pattern.
Oil ring
ring gap
ring gap
Oil ring
ring gap
Fig. 74
Second ring
Fig. 75
Crankcase
Surface where
ThreeBond 1216
should be applied
P 23/26
ring gap
Top ring
Second ring
white marking
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