XII Cylinder Block and Piston

Preparatory data 12.1

Fault diagnosis 12.2

Cylinder block 12.3

Piston 12.4

Preparatory Data

Function of cylinder block:

Cylinder block provides the space for gas compression, combustion and expansion and guides piston movement. It also transfers part of heat in the cylinder to surrounding coolant.

Function of piston:

1. Piston can bear the pressure generated by combustion of mixed combustible gas in the cylinder and transmit the pressure to connecting rod to drive crankshaft to rotate.

2. It forms a combustion chamber with cylinder head.

Precautions on Operation

All the components shall be cleaned before inspection and test, and purged with high-pressure air.

Table of standard values of baseline projects and allowable limit

Item	Standard Value	Service Limit
Cylinder	ID	60-60.013	60.063
Cylindricity	0.005	0.025
Roundness	0.004	0.025
Flatness	0.03	0.05
Piston OD(measuring point)	59.94-59.95	-
Piston pin hole ID	15.002-15.008	15.04
Piston pin OD	14.994-14.999	14.976
Clearance between piston and piston pin	0.003-0.014	0.064
Clearance between piston ring and ring groove	Top ring	0.03-0.07	0.12
Second ring	0.03-0.07	0.12
Joint clearance of piston rings	Top ring	0.15-0.3	0.4
Second ring	0.25-0.4	0.5
Oil ring	0.15-0.6	-
Connecting rod small end ID	15.01-15.018	15.068
Clearance between linkage rod and piston pin	0.011-0.024	0.092

Fault Diagnosis

Low compression pressure White smoke from exhaust pipe

Worn, burnt or broken piston Worn or damaged piston ring

Work or damaged cylinder and piston Worn or damaged cylinder and piston

Broken washer, air leakage between crankcase and gas

Higher compression pressure Noisy piston

Too much carbon deposited in the combustion chamber Damaged cylinder, piston and piston ring

Worn piston pin hole and piston pin

12.3 Cylinder Head

Removal

Remove cylinder block

Inspection

Inspect wear of cylinder inner wall.

If it is seriously worn, replace it.

 

 

Remove washer and location pin.

 

Piston

Removal

Remove piston pin retainer.

Attention: Please do not drop the retainer into crankcase during removal.

Take out piston pin and remove piston.

Remove piston ring.

Inspect piston, piston pin and piston ring.

Attention:

Please do not break or hurt piston ring.

Remove deposited carbon inside the piston ring.

 

Install the piston ring.

Measure the clearance between piston ring and piston ring groove.

Allowable limit: First ring: 0.12 mm

Second ring: 0.12 mm

 

Remove piston ring and install all the piston rings onto bottom of cylinder.

Attention:

Compress piston rings into the cylinder with piston head.

Measure the joint clearance between piston rings.

Allowable limit: First ring: 0.4 mm

Second ring: 0.5 mm

 

Measure piston pin hole ID.

Allowable limit: ¦µ15.04 mm

 

 

Measure piston pin OD.

Allowable limit: §¶14.976mm

Measure the clearance between piston pin hole and piston pin.

Allowable limit: 0.064mm

 

Measure piston OD

 

Attention:

Measuring position forms a 90Ўг angle with piston pin, about 11mm below piston skirt.

 

Allowable limit: ¦µ59.93mm

Inspect wear and scratch on inner wall of cylinder.

 

Attention:

Measure cylinder ID at three positions, i.e. upper, intermediate and lower positions. The position forms a 90Ўг angle with piston pin.

Allowable limit: ¦µ60.063mm

Measure the clearance between cylinder and piston. Take the maximum clearance as standard.

Allowable limit: 0.07mm

 

Measure the roundness of cylinder inner wall (internal diameter difference between X direction and Y direction).

Allowable limit: 0.01mm

Measure the cylindricity of inner wall of cylinder (internal diameter difference of three positions (upper, intermediate and lower) along X direction or Y direction).

Allowable limit: 0.01mm

 

 

 

 

Check flatness of cylinder surface.

Allowable limit: 0.05mm

 

Measure Connecting rod small end ID.

Allowable limit: ¦µ15.068mm

 

Installation of piston

Install location pin.

Apply engine oil evenly on each piston ring and piston. Install piston to its place with bevel upward.

Attention:

Piston shall not be scratched and piston ring shall not be broken.

When the piston ring is installed, it can rotate freely in the piston ring groove.

 

 

Scrape the washer attached to the crankcase.

Attention:

No foreign matters can be dropped into the crankcase.

Install piston, piston pin and piston pin retainer.

Attention:

The larger side of the groove at the piston head should be installed towards the intake valve.

 

 

Install Cylinder

Install washer and location pin onto the crankcase.

Apply evenly engine oil on inner wall of cylinder, piston and piston ring.

Install carefully the piston ring into the cylinder.

Attention:

Do not hurt piston ring.

XIII Crankcase

Preparatory data 13.1

Fault diagnosis 13.2

Crankcase 13.3

Clutch 13.4

Gearshift mechanism 13.5

Bent axle connecting rod assembly 13.6

Variable speed chamber 13.7

Preparatory Data

Function of crankcase:

Crankcase is the force bearing part of engine. It is mainly used to support crankshaft, clutch, transmission, cylinder block and cylinder head. It bears impact from combustion and inertia force from movement of crankshaft connecting rod; and forms a partial enclosed space (for air and oil).

Suspension hole is set on the crankcase, which can be connected with the suspension hole in the vehicle block so that the engine can be linked together with frame and other parts.

 

Precautions on Operation:

Crankcase is a thin-wall casting part. Avoid impact on it during operation in case it may be distorted or broken.

Clean carefully all the components before inspection and test and purge them with high-pressure gas.

Drain the lubricating oil from crankcase before working on it.

Table of standard values of baseline projects and allowable limit Unit: mm

Item	Standard	Allowable limit
Bent axle connecting rod assembly, clutch	Clearance between the left and the right of the big end of the connecting rod	0.1-0.35	0.5
Connecting rod big end radial clearance	0.008-0.018	-
Jump	-	0.03
Thickness of friction plate	2.8-2.9	2.5
Flatness of running friction plate	0.04	0.2
Length of pressure spring	30.4-31.6	29.7
Thickness of surface needle roller	1.88-2	1.8
Gearshift mechanism	Outer diameter of shifting fork axis	9.98-9.995	9.96
Diameter of bore of shifting fork	10-10.018	10.05
Thickness of shifting fork	4.8-4.9	4.6
Outer diameter of gearshift hub	41.8-42	41.75
Width of gearshift hub locked groove	5.45-5.55	5.7

Fault Diagnosis

Low compression pressure

Crankcase air leakage

Engine overheat

Clutch clipping

Poor lubrication

Failure in gear

Gear shift fork broken or deformation

Shifting fork guide pin broken

Wheel gear convex claw worn

Auto-off gear

The joint claw is worn with the edge into a fillet.

Force of return spring of the speed shifting mechanism is weakened.

The spline tooth of spline shaft and the spline groove of sliding gear are worn, resulting a greater axial force in the gear while working.

Gearshift hub and shifting fork are worn.