XI. Cylinder Block and Piston 92
11.1 Preparing documents 92
Work Instructions
All parts shall be cleaned and blown with high-pressure gas before check.
Function of the cylinder block:
The cylinder block provides space for gas compression, combustion andexpansion, and also guides the piston movement.
It transfers part of heat inside the cylinder to cooling medium around.
Function of the piston:
1．It is able to sustain pressure caused by combustion of mixed combustible gas in the cylinder and transfer such pressure to the connecting rod which drives the crankshaft to rotate.
2．It forms a combustion chamber with the cylinder cover.
Preparing Principles
Unit: mmItem Standard Limit for use
Cylinder Inner diameter 52.40-52.413 52.413 Cylindricity 0.004 0.004 Roundness 0.005 0.005 Flatness 0.05 0.05 Piston Piston ring Piston pin
Marked direction ―IN‖ opposite the intake
valve /
Outer diameter measuring point
52.36－52.37 (7mm below the bottom of the
piston skirt
52.37
Inner diameter of the piston pin
hole 14.002－14.008 14.04
Outer diameter of the piston pin 13.994-13.999 13.97 Clearance between the cylinder and
the piston 0.03-0.053 0.053
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between the piston ring and the ring slot
Ring 2 0.03－0.07 0.10
Joint gap of the piston ring
Ring 1 0.10-0.25 0.50
Ring 2 0.20-0.35 0.60
Oil ring 0.1－0.6 Clearance between the piston and
the piston pin 0.003-0.014 0.03
Inner diameter of the smaller end
of the connecting rod 14.010－14.018 14.04 Clearance between the connecting
rod and the piston pin 0.011－0.024 0.05
11.2 Failure diagnosis
Low compression pressure White smoke from the exhaust pipe
Abrasive, burnt or ruptured piston Abrasive or damaged piston ring Abrasive or damaged cylinder or piston Abrasive or damaged cylinder or piston Damaged spacer or crankcase leakage
Over-high compression pressure Abnormal noise of the piston
Too much carbon deposit in the combustion chamber Damaged cylinder, piston or piston ring Abrasive piston pin hole and piston pin
11.3 Cylinder block
119.1 Disassembly of the cylinder block
Remove the cylinder head, spacer for the cylinder cover and locating pin.
Remove the main chain plate. Remove the cylinder.
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119.2 Cylinder block check
Check the abrasion of the inner wall of the cylinder. If it is serious, replace it.
Remove the spacer and the locating pin.
Remove any residual spacer attached to the cylinder.
（定位销：locating pin 垫片：spacer）
11.4 Piston
120.1 Disassembly
Remove the retainer ring of the piston.
Note: during assembly, do not make the retainer ring fall into the crankcase.
Remove the piston pin and the piston.
（活塞销：piston pin 挡圈：retainer ring）
Check the piston, piston pin and piston ring. Remove the piston ring.
Note:
Do not rupture or damage the piston ring.
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Install the piston ring.
Measure the clearance between the piston ring and the piston ring groove.
Limit for use: top ring: 0.10mm. Ring 2: 0.10mm.
（活塞：piston 测试规：gauge 推入：push in 活塞环：piston ring）
Remove the piston ring and install each piston ring at the cylinder bottom.
Note: Press the piston ring into the cylinder with the piston head.
Measure the joint gap of the piston ring.
Limit for use: 0.5mm.
（测试规：gauge 活塞环：piston ring）
Measure the inner diameter of the piston pin hole.
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Measure the outer diameter of the piston pin.
Limit for use: 13.97mm.
Clearance between the piston pin hole and the piston pin.
Limit for use: 0.03mm.
Measure the outer diameter of the piston.
Note:
The measuring point shall be at 90 degree with the piston pin, and at 7mm below the piston skirt.
Limit for use：52.37mm。
Check whether the inner wall of the cylinder is scratched or abraded.
Note:
It is at 90 degree with the piston pin. Measure the inner diameter of the cylinder at the top, middle and bottom points.
Limit for use: 52.413mm。
Measure the clearance between the cylinder and the piston. Record the maximum value.
Limit for use: 0.053mm。
（测试计：tester）
90°
7mm
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Measure the roundness of the inner wall of the cylinder (inner diameter difference at X direction and Y direction).
Limit for use: 0.005mm。
Measure the cylindricity of the inner wall of the cylinder (inner diameter difference at the top, middle and bottom points of X direction or Y direction).
Limit for use: 0.004mm。
Check the flatness of the cylinder surface.
Limit for use: 0.05mm。
（直尺：ruler 测试规：gauge）
Measure the inner diameter of the smaller end of the connecting rod.
Limit for use: 14.04mm。
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11.5 Piston installation
Install the locating pin.
Apply fuel to each piston ring and piston. Install the piston ring with marked side upward.
Note:
Do not scratch the piston or break the piston ring.
After the piston ring is installed, it shall be able to rotate freely in the piston ring groove.
（顶环：top ring 第二环：ring 2 油环：oil ring）
Open the right cover and remove the starting lever assembly.
Remove any residual spacer attached to the crankcase.
Note:
Do not make any object fall into the crankcase. Install the piston, piston pin and retainer ring. Note:
Install the piston with its top mark ―IN‖ towards the intake valve.
（IN 记号： IN mark）
11.6 Cylinder installation
Install the spacer and the locating pin on the crankcase.
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Evenly apply fuel to the inner wall of the cylinder, piston and piston ring.
Carefully install the piston ring into the cylinder.
Note:
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