Kymco MO GD125, MO GD 150 Service Manual - chap 06 (testa cilindro valvole)

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Page 1

6. CYLINDER HEAD/VALVES

6-0

GRAND DINK 125/15 0

6 .

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CYLINDER HEAD/VALVES

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SCHEMATIC DRAWING ---------------------------------------------- 6- 1

SERVICE INFORMATION -------------------------------------------- 6- 2

TROUBLESHOOTING ------------------------------------------------- 6- 3

CYLINDER HEAD COVER REMOVAL ----------------------------- 6- 4

CAMSHAFT REMOVAL----------------------------------------------- 6- 4

CYLINDER HEAD REMOVAL --------------------------------------- 6- 6

CYLINDER HEAD DISASSEMBLY --------------------------------- 6- 7

CYLINDER HEAD ASSEMBLY -------------------------------------- 6- 8

CYLINDER HEAD INSTALLATION -------------------------------- 6- 9

CAMSHAFT INSTALLATION---------------------------------------- 6-10

CYLINDER HEAD COVER INSTALLATION---------------------- 6-11

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6. CYLINDER HEAD/VALVES

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SCHEMATIC DRAWING

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6. CYLINDER HEAD/VALVES

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SERVICE INFORMATION

GENERAL INSTRUCTIONS

• The cylinder head can be serviced with the engine installed in the frame. Coolant in the radiator

and water jacket must be drained first.

• When assembling, apply molybdenum disulfide grease or engine oil to the valve guide movable

parts and valve arm sliding surfaces for initial lubrication.

• The valve rocker arms are lubricated by engine oil through the cylinder head engine oil passages.

Clean and unclog the oil passages before assembling the cylinder head.

• After disassembly, clean the removed parts and dry them with compressed air before inspection.

• After removal, mark and arrange the removed parts in order. When assembling, install them in the

reverse order of removal.

SPECIFICATIONS

Standard (mm)

Service Limit (mm)

Item

SH30DA

SH25DA

SH30DA

SH25DA

0.10

ææEX

0.10

Cylinder head compression pressure

15kg/cm_

Cylinder head warpage

0.05

0.05IN30.8763

30.8763

30.75

30.75EX30.4081

30.4081

30.26

10.00_ 10.018

10.10

10.00_ 10.018

10.10

Valve rocker arm shaft

9.972_ 9.987

9.9

O.D.EX9.972_ 9.987

9.972_ 9.987

9.9

9.9IN1.2

1.2

1.8

1.8EX1.2

1.2

1.8

4.990_ 4.975

4.925

4.970_ 4.955

4.915

5.00_ 5.012

5.03

5.00_ 5.012

5.03

Valve stem-to-guide

0.010_ 0.037

0.08

clearance

0.030_ 0.057

0.10

TORQUE VALUES

Cylinder head cap nut 19.6N-m Apply engine oil to threads Valve clearance adjusting nut 8.8N-m Apply engine oil to threads Cylinder head cover bolt 7.8_ 11.8N-m

SPECIAL TOOLS

Valve spring compressor Valve seat cutter, 24.5mm 45° IN-EX Valve seat cutter, 25mm Plane cutter 37.5° EX Valve seat cutter, 22mm Plane cutter 37.5° EX Valve seat cutter, 26mm Plane cutter 63.5° IN/EX Cutter clip Valve guide driver Valve guide reamer

Valve clearance (cold)

Valve rocker arm I.D.

Valve stem O.D.

Valve guide I.D.

Camshaft cam height

Valve seat width

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6. CYLINDER HEAD/VALVES

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TROUBLESHOOTING

• The poor cylinder head operation can be diagnosed by a compression test or by tracing engine

top-end noises.

Poor performance at idle speed White smoke from exhaust muffler

• Compression too low • Worn valve stem or valve guide

• Damaged valve stem oil seal

Compression too low

• Incorrect valve clearance adjustment Abnormal noise

• Burned or bend valves • Incorrect valve clearance adjustment

• Incorrect valve timing • Sticking valve or broken valve spring

• Broken valve spring • Damaged or worn camshaft

• Poor valve and seat contact • Worn cam chain tensioner

• Leaking cylinder head gasket • Worn camshaft and rocker arm

• Warped or cracked cylinder head

• Poorly installed spark plug

Compression too high

• Excessive carbon build-up in combustion

chamber

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6. CYLINDER HEAD/VALVES

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CYLINDER HEAD COVER REMOVAL

Remove the center cover. (!2-3) Remove the met-in box. (!2-3) Remove the cylinder head cover four bolts and then remove the cylinder head cover.

CAMSHAFT REMOVAL

Turn the A.C. generator flywheel so that the “T” mark on the flywheel aligns with the index mark on the crankcase. Hold the round hole on the camshaft gear facing up and the location is the top dead center on the compression stroke. Remove the two bolts attaching cam chain tensioner and the tensioner.

First remove the two bolts between the cylinder head and cylinder. Then, remove the four cap nuts attaching the cylinder head.

Remove the camshaft holder and dowel pins.

Cylinder Head Cover

Bolt

Cam Chain Tensioner

Round Hole

Camshaft Holder

Bolts

• Diagonally loosen the cylinder

head cap nuts in 2 or 3 times.

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Camshaft Holder

Cap Nuts

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Remove the camshaft gear from the cam chain to remove the camshaft.

CAMSHAFT INSPECTION

Check each cam lobe for wear or damage. Measure the cam lobe height.

Service Limits:

SH30DA

IN: 30.75mm replace if below

SH25DA

EX:30.26mm replace if below

Check each camshaft bearing for play or damage. Replace the camshaft assembly with a new one if the bearings are noisy or have excessive play.

CAMSHAFT HOLDER DISASSEMBLY

Take out the valve rocker arm shafts using a 6mm bolt. Remove the valve rocker arms.

Cam Chain

Camshaft Gear

Camshaft Bearings

6mm Bolt

Valve Rocker Arms

Rocker Arm Shafts

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CAMSHAFT HOLDER INSPECTION

Inspect the camshaft holder, valve rocker arms and rocker arm shafts for wear or damage.

Measure the I.D. of each valve rocker arm. Service Limits: IN: 10.10mm replace if over

EX: 10.10mm replace if over Measure each rocker arm shaft O.D. Service Limits: IN: 9.90mm replace if below

EX: 9.90mm replace if below

CYLINDER HEAD REMOVAL

First drain the coolant from the radiator and water jacket, then remove the thermostat water hose. Remove the camshaft. (!6-4) Remove the carburetor and intake manifold. Remove the bolt attaching the thermostat housing and the thermostat housing. Remove the cylinder head.

Remove the dowel pins and cylinder head gasket. Remove the cam chain guide. Remove all gasket material from the cylinder head mating surface.

Bolt

Intake Manifold

Cam Chain Tensioner Slipper

Camshaft Holder

If the valve rocker arm contact surface is worn, check each cam lobe for wear or damage.

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Be careful not to drop any gasket material into the engine.

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Rocker Arm Shafts

Cylinder

Cylinder Head Gasket

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CYLINDER HEAD DISASSEMBLY

Remove the valve spring cotters, retainers, springs, spring seats and valve stem seals using a valve spring compressor.

Remove carbon deposits from the exhaust port and combustion chamber.

Valve Spring Compressor

Cylinder Head

• Be sure to compress the valve

springs with a valve spring compressor.

• Mark all disassembled parts to

ensure correct reassembly.

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Be careful not to damage the cylinder head mating surface.

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Exhaust Port

Combustion Chamber

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INSPECTION

CYLINDER HEAD Check the spark plug hole and valve areas for

cracks. Check the cylinder head for warpage with a straight edge and feeler gauge.

Service Limit: 0.05mm repair or replace if

over

VALVE SPRING FREE LENGTH Measure the free length of the inner and outer

valve springs. Service Limits:

Inner (IN, EX) : 29.3mm replace if below Outer (IN, EX): 32.0mm replace if below

VALVE /VALVE GUIDE Inspect each valve for bending, burning,

scratches or abnormal stem wear. Check valve movement in the guide.

Measure each valve stem O.D. Service Limits: IN: 4.925mm replace if

below EX: 4.915mm replace if below

CYLINDER HEAD ASSEMBLY

Install the valve spring seats and stem seals. Lubricate each valve stem with engine oil and

insert the valves into the valve guides. Be sure to install new valve stem seals.

Straight Edge

Feeler Gauge

Valve Spring Compressor

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Tap the valve stems gently with a plastic hammer to firmly seat the cotters.

CYLINDER HEAD INSTALLATION

Install the cam chain guide. Install the dowel pins and a new cylinder head gasket.

Install the cylinder head and take out the cam chain

Assemble the camshaft holder. First install the intake and exhaust valve rocker arms; then install the rocker arm shafts.

Gasket

Cam Chain Guide

Valve Rocker Arms

Plastic Hammer

Cam Chain

Cylinder Head

Camshaft Holder

Be careful not to damage the valves.

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Dowel Pins

• Install the exhaust valve rocker

arm shaft on the “EX” side of the camshaft holder and the exhaust rocker arm shaft is shorter.

• Clean the intake valve rocker arm

shaft off any grease before installation.

• Align the cutout on the exhaust

valve rocker arm shaft with the bolt of the camshaft holder.

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CAMSHAFT INSTALLATION

Turn the A.C. generator flywheel so that the “T” mark on the flywheel aligns with the index mark on the crankcase. Keep the round hole on the camshaft gear facing up and align the punch marks on the camshaft gear with the cylinder head surface (Position the intake and exhaust cam lobes down.) and install the cam chain over the camshaft gear.

Install the dowel pins.

Install the camshaft holder, washers and nuts on the cylinder head. Tighten the four cylinder head nuts and the two bolts between the cylinder head and cylinder.

Torque: Cylinder head cap nut: 19.6N-m

Cylinder & cylinder head bolt:

7.8_ 11.8N-m

Dowel Pins

Nut

Washer

Punch Marks

Bolts

Cam Chain

Round Hole

• Apply engine oil to the threads

of the cylinder head cap nuts.

• Diagonally tighten the cylinder

head cap nuts in 2_ 3 times.

• First tighten the cylinder head

cap nuts and then tighten the bolts between the cylinder and cylinder head to avoid cracks.

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Install a new cam chain tensioner gasket. Release the lock pawl and push the push rod

all the way in.

Install the cam chain tensioner and tighten the two bolts. Install the tensioner spring and tighten the sealing bolt.

Torque: 2.9_ 5.8N-m

CYLINDER HEAD COVER INSTALLATION

Adjust the valve clearance. (!3-6) Install a new cylinder head cover O-ring and install the cylinder head cover.

Install and tighten the cylinder head cover bolts.

Torque: 7.8_ 11.8N-m

Cam Chain Tensioner

Sealing Bolt

Bolt

Lock Pawl

Push Rod

Gasket

Cam Chain Tensioner

Spring

Cylinder Head Cover

O-ring

Be sure to install the O-ring into the groove properly.

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Kymco MO GD125, MO GD 150 Service Manual - chap 06 (testa cilindro valvole)

Specifications and Main Features

Frequently Asked Questions

User Manual