Kymco MO KXR 50 Service Manual - chap 08 (cilindro pistone)

8. CYLINDER/PISTON

8-0

Mongoose/KXR 90/50

8

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CYLINDER /PISTON

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SERVICE INFORMATION (Mongoose/KXR 90)-------------------- 8- 3

SERVICE INFORMATION (Mongoose/KXR 50)-------------------- 8- 4

CYLINDER/PISTON (Mongoose/KXR 90) --------------------------- 8- 5

CYLINDER HEAD (Mongoose/KXR 50) ----------------------------- 8-10

CYLINDER/PISTON (Mongoose/KXR 50) --------------------------- 8-13

8

8. CYLINDER/PISTON

8-1

Mongoose/KXR 90/50

Mongoose/KXR 90

8. CYLINDER/PISTON

8-2

Mongoose/KXR 90/50

Mongoose/KXR 50

8. CYLINDER/PISTON

8-3

Mongoose/KXR 90/50

SERVICE INFORMATION (Mongoose/KXR 90)

GENERAL INSTRUCTIONS

• The cylinder and piston can be serviced with the engine installed in the frame.

• Before disassembly, clean the engine to prevent dust from entering the engine.

• Remove all gasket material from the mating surfaces.

• Do not use a driver to pry between the cylinder and cylinder head, cylinder and crankcase.

• Do not damage the cylinder inside and the piston surface.

• After disassembly, clean the removed parts before inspection. When assembling, apply the

specified engine oil to movable parts.

SPECIFICATIONS

Standard (mm)

Service Limit (mm)

I.D.

47.00_ 47.01

47.1
Warpageæ0.05
Cylindricity

æ

0.05
True roundness

æ

0.05

Ring-to-groove

Top

0.015_ 0.055

0.09
clearance

Second

0.015_ 0.055

0.09
Top

0.15_ 0.3

0.5

Piston,

Ring end gap

Second

0.3_ 0.45

0.65

piston ring

Oil ring

0.2_ 0.7

0.9

Piston O.D.

46.97_ 46.99

46.9
Piston O.D. measuring position

4mm from bottom of skirt

æ

.

Piston-to-cylinder clearance

0.010_ 0.040

0.1

Piston pin hole I.D.

13.002_ 13.008

13.04

Piston pin O.D

12.994_ 17.000

12.96

Piston-to-piston pin clearance

0.002_ 0.014

0.02

Connecting rod small end I.D. bore

13.016_ 13.034

13.06

TROUBLESHOOTING

• When hard starting or poor performance at low speed occurs, check the crankcase breather for

white smoke. If white smoke is found, it means that the piston rings are worn, stuck or broken.

Compression too low or uneven

compression Excessive smoke from exhaust muffler

• Worn, stuck or broken piston rings • Worn or damaged piston rings

• Worn or damaged cylinder and piston • Worn or damaged cylinder and piston

Compression too high Abnormal noisy piston

• Excessive carbon build-up in combustion • Worn cylinder, piston and piston rings

chamber or on piston head

• Worn piston pin hole and piston pin

Cylinder

8. CYLINDER/PISTON

8-4

Mongoose/KXR 90/50

SERVICE INFORMATION (Mongoose/KXR 50)

GENERAL INSTRUCTIONS

• The cylinder head, cylinder and piston can be serviced with the engine installed in the frame.

• Before disassembly, clean the engine to prevent dust from entering the engine.

• Remove all gasket material from the mating surfaces.

• Do not use a driver to pry between the cylinder and cylinder head, cylinder and crankcase.

• Do not damage the cylinder inside and the piston surface.

• After disassembly, clean the removed parts before inspection. When assembling, apply the

specified engine oil to movable parts.

SPECIFICATIONS

Item

Standard (mm)

Service Limit (mm)

Cylinder head warpage

æ

0.10

Piston O.D.(3mm from bottom of piston

38.960_ 38.965

38.90

Cylinder-to- piston clearance

0.035_ 0.05

0.10

Piston pin hole I.D.

12.002_ 12.008

12.03

Piston pin O.D.

11.994_ 12.0

11.98

Piston-to-piston pin clearance

0.002_ 0.014

0.03

Piston ring end gap (top/second)

0.10_ 0.25

0.40

Connecting rod small end I.D.

17.005_ 17.017

17.03

Cylinder bore

39.005_ 39.01

39.05

TORQUE VALUES

Cylinder head bolt 0.8_ 1.2kg-m
Spark plug 1.1_ 1.7kg-m

TROUBLESHOOTING

Compression too low, hard starting
or poor performance at low speed Abnormal noisy piston

• Leaking cylinder head gasket • Worn cylinder and piston

• Loose spark plug • Worn piston pin or piston pin hole

• Worn, stuck or broken piston and piston rings • Worn connecting rod small end bearing

• Worn or damaged cylinder and piston

Compression too high, overheating
or knocking Abnormal noisy piston rings

• Excessive carbon build-up in cylinder head • Worn, stuck or broken piston rings
or on piston head • Worn or damaged cylinder

8. CYLINDER/PISTON

8-5

Mongoose/KXR 90/50

CYLINDER/PISTON
(Mongoose/KXR 90)

REMOVAL

Remove the cylinder head. (Refer to the
chapter 7)

Remove the two dowel pins and cylinder
head gasket.

Remove cam chain guide and then remove
cylinder.

Remove the cylinder gasket and dowel pins.
Clean any gasket material from the cylinder
surface.

Remove the piston pin clip.

Press the piston pin out of the piston and
remove the piston.

Dowel Pins

Gasket

Cam Chain Guide

Cylinder

Dowel Pins

Gasket

Piston

Clip

Piston Pin

Be careful not to drop foreign matters
into the crankcase.

°Ø

Place a clean shop towel in the crankcase
to keep the piston pin clip from falling
into the crankcase.

°Ø

Towel