Disassembly And Reassembly Of The Piston And Piston Rings - Hitachi CM 75EAP Service Manual

13. Disassembly and reassembly of the piston and piston rings

[Tools required]
• Long-nose pliers
• Jig J-381 (Code No. 6600412) (Piston pin extractor ass'y)
• Hex. socket hd. bolt M6
• Round bar about 11.8 mm in diameter (Borer 12 mm in diameter, etc.)
(1) Disassembly
• Remove the two Cir Clips [171] by using long-nose
pliers.
• Fit an extra hex. socket hd. bolt M6 to the pushing
end of the Piston Pin [173]. Turn the pin extracting
bolt of the jig J-381 to push out the Piston Pin [173].
NOTE: Be careful not to damage the Piston
(51.5) [172].
• Pull out the two Piston Rings [170] by widening
their closed gap portions.
NOTE: Do not widen the gap too much. Doing
so runs the risk of breaking the ring.
(2) Reassembly
• Be careful not to damage the peripheral surface of the Piston (51.5) [172] when disassembled.
Remove carbon dust from the top of the Piston (51.5) [172] and clean the piston with gasoline.
• If the two Piston Rings [170] do not move smoothly, remove carbon dust from the ring grooves of the
Piston (51.5) [172] and the two Piston Rings [170], and fully clean the parts with gasoline.
• Follow the steps below to insert the Piston Pin [173]. See the following figure "Reassembly of the
piston."
(a) Mount the jig J-381 on the Piston (51.5) [172] and fit an extra hex. socket hd. bolt M6 into the
pushing end of the Piston Pin [173].
(b) Mount Needle Bearing (A) [2] on the connecting rod small end and cover it with the Piston (51.5)
[172]. Align the triangular arrow on top of the Piston (51.5) [172] with the direction of the exhaust
port of the Cylinder [146]. Insert a round bar about 11.8 mm in diameter (a borer 12 mm in diameter,
etc.) into the Piston (51.5) [172] opposite the side where the Piston Pin [173] is inserted, in order to
prevent Needle Bearing (A) [2] from becoming misaligned.
(c) With a round bar 11.8 mm in diameter inserted, turn the pin extracting bolt of the jig J-381 clockwise
and push in the bolt just before the circlip mounting groove of the Piston (51.5) [172], being careful
not to slant the Piston Pin [173].
• Do not reuse the two Cir Clips [171].
• Fit the tips of the two Cir Clips [171] into the grooves of the Piston (51.5) [172] by using long-nose
pliers, and fit the entire clips into the grooves by turning them along the grooves.
• Align the openings of the two Piston Rings [170] to the knock pins of the Piston (51.5) [172].
• Apply a small quantity of two-cycle oil to Needle Bearing (A) [2] after mounting the Piston (51.5)
[172].
• Disassembly of the piston
Hex. socket
hd. bolt M6
-20-
Jig J-381
Pin extracting bolt