sm - kymco vitality 50 - chapter 07 (2-stroke cylinder - head - valves)

7. CYLINDER HEAD (2-STROKE)/CYLINDER/PISTON

7-0

VITALITY 50

7 __________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

CYLINDER HEAD (2-STROKE)/CYLINDER/PISTON__________________________________________________________________________________

SERVICE INFORMATION (2-STROKE).................................... 7- 3

SERVICE INFORMATION (4-STROKE).................................... 7- 4

CYLINDER HEAD (2-STROKE) ............................................... 7- 5

CYLINDER/PISTON (2-STROKE)............................................. 7- 8

CYLINDER/PISTON (4-STROKE) ----------------------------------- 7-13

7


7-1

VITALITY 50

(2-STROKE)

Torque: 1.0_ 1.2kg-m

Torque: 1.1_ 1.7kg-m (cold)


7-2

VITALITY 50

(4-STROKE)


7-3

VITALITY 50

SERVICE INFORMATION (2-STROKE)

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 Standard (mm) Service Limit (mm)

Item 2-Stroke

SF10AFCylinder head warpage 0.10

Piston O.D.(5mm from bottom of pistonskirt)

38.970_ 38.955 38.90

Cylinder-to- piston clearance 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 0.03

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 39.0_ 39.025 39.05

TORQUE VALUES

Cylinder head bolt 1.0_ 1.2kg-mExhaust muffler joint lock nut 1.0_ 1.4kg-mExhaust muffler lock bolt 3.0_ 3.6kg-mSpark plug 1.1_ 1.7kg-m

TROUBLESHOOTING

Compression too low, hard startingor 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, overheatingor 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


7-4

VITALITY 50

SERVICE INFORMATION (4-STROKE)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.

SPECIFICATIONSStandard (mm) Service Limit (mm)

I.D. 39.00_ 39.01 39.1Warpage 0.05Cylindricity 0.05True roundness 0.05Ring-to-groove Top 0.015_ 0.055 0.09clearance Second 0.015_ 0.055 0.09

Top 0.15_ 0.3 0.5Piston, Ring end gap Second 0.3_ 0.45 0.65piston ring Oil ring 0.2_ 0.7 0.9

Piston O.D. 38.975_ 38.99 38.9Piston O.D. measuring position 4.5mm from bottom of

skirt

. Piston-to-cylinder clearance 0.010_ 0.040 0.1Piston pin hole I.D. 13.002_ 13.008 13.04

Piston pin O.D 12.994_ 13.000 12.96Piston-to-piston pin clearance 0.002_ 0.014 0.02Connecting 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 forwhite smoke. If white smoke is found, it means that the piston rings are worn, stuck or broken.

Compression too low or unevencompression 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 pistonCompression 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


7-5

VITALITY 50

CYLINDER HEAD (2-STROKE)REMOVALRemove the rear body cover. (13-6)

Remove the spark plug cap

Remove the fan cover. (8-3)Remove the exhaust muffler. (13-10)

Remove the bolt from the engine hood, thenremove the engine hood.

Remove the spark plug.Remove the cylinder head bolts and thecylinder head.

Remove the cylinder head gasket.

Cylinder head Bolts

Spark Plug Cap

Fan Cover/Engine Hood

Bolts

Cylinder Head

Spark Plug

Loosen the bolts diagonally in 2 or 3times.

°Ø


7-6

VITALITY 50

COMBUSTION CHAMBERDECARBONIZING

Remove the carbon deposits from thecombustion chamber

CYLINDER HEAD INSPECTION

Check the cylinder head for warpage with astraight edge and feeler gauge.Service Limit: 0.10mm replace if over

CYLINDER HEAD INSTALLATIONInstall a new cylinder head gasket onto thecylinder.Install the cylinder head on the cylinderproperly.

Avoid damaging the combustionchamber wall and cylinder matingsurface.

°Ø

Be careful not to damage the matingsurfaces.

°Ø

Cylinder head Gasket

Combustion Chamber

Mating Surface


7-7

VITALITY 50

Cylinder Head Bolts InstallationInstall and tighten the cylinder head boltsdiagonally in 2 or 3 times.Torque: 1.0_ 1.2kg-mInstall the spark plug.Torque: 1.1_ 1.7kg-m

Engine Hood InstallationInstall the engine hood. (7-5)Install the spark plug cap. (7-5)Remove the exhaust muffler. (13-10)

Perform the following inspections afterinstallation:• Compression test• Abnormal engine noise

• Cylinder air leaks

Cylinder head Bolts

Bolts

Bolt

Cylinder Head

Spark Plug

Spark Plug

Engine Hood


7-8

VITALITY 50

CYLINDER/PISTON

(2-STROKE)CYLINDER REMOVALRemove the cylinder head. (7-5)Remove the exhaust muffler. (13-10)

Remove the cylinder.Remove the cylinder gasket.

PISTON REMOVALRemove the piston pin clip to remove thepiston pin and piston.

Spread each piston ring and remove bylifting it up at a point just opposite the gap.Remove the expander.

Piston Pin Clip

Piston Piston Pin

Cylinder

Do not pry between the cylinder andcrankcase or strike the fins.

°Ø

•Do not damage or scratch the piston.•Do not apply side force to the

connecting rod when removing thepiston pin.

• Place clean shop towels in thecrankcase to keep the piston pin clipfrom falling into the crankcase.

°Ø


7-9

VITALITY 50

CYLINDER/PISTON INSPECTIONCheck the cylinder and piston for wear ordamage.Clean carbon deposits from the exhaustport area.

Measure the cylinder bore at three levels ofA, B and C in both X and Y directions.Avoid the port area. Take the maximumfigure measured to determine the cylinderbore.Service Limit: 39.05mm replace if over

Inspect the top of the cylinder for warpage.Service Limit: 0.10mm replace if over

Be careful not to damage the cylinderinside wall.

°Ø


7-10

VITALITY 50

Measure the piston O.D. at a point 5mmfrom the bottom of the piston skirt.Service Limit: 38.90mm replace if below

Measure the piston-to-cylinder clearance.Service Limit: 0.10mm replace if over

Measure the piston pin hole I.D.Service Limit: 12.03mm replace if over

Measure the piston pin O.D.Service Limit: 11.98mm replace if below

Measure the piston-to-piston pin clearance.Service Limit: 0.03mm replace if over

The cylinder has a “A” mark or no markon it. When replacing the cylinder with anew one, use a cylinder having the samemark as the old one.

°Ø

A Mark


7-11

VITALITY 50

PISTON RING INSPECTIONMeasure each piston ring end gap.Service Limits:Top/Second: 0.40mm replace if over

CONNECTING ROD SMALL ENDINSPECTIONInstall the piston pin and bearing in theconnecting rod small end and check forexcessive play.Measure the connecting road small end I.D.Service Limit: 17.03mm replace if over

PISTON/CYLINDER INSTALLATIONFirst install the expander in the second ringgroove.Then install the top and second rings intheir respective ring grooves.The piston rings should be pressed into thegrooves with even force.After installation, check and make sure thateach ring is flush with the piston at severalpoints around the ring.A ring that will not compress means thatthe ring groove has carbon deposits in it andshould be cleaned.

Set each piston ring squarely into thecylinder using the piston and measurethe end gap.

°Ø

Expander

Top Ring (1st Ring)Piston

Second Ring


7-12

VITALITY 50

Install a new cylinder gasket on the matingsurface between the cylinder and crankcase.

Make sure that the ring end gaps are alignedwith the piston ring pins in the ringgrooves.

Lubricate the cylinder inside and pistonrings with engine oil and install the pistoninto the cylinder while compressing thepiston rings.

Install the cylinder head.Torque: 1.0_ 1.2kg-mInstall the exhaust muffler and tighten theexhaust muffler joint lock nuts.Torque: 1.0_ 1.4kg-mTighten the exhaust muffler lock bolts.Torque: 3.0_ 3.6kg-m

Cylinder Gasket

Ring Pins

Be careful not to damage the piston.°Ø


7-13

VITALITY 50

CYLINDER/PISTON(4-STROKE)REMOVALRemove the cylinder head. (Refer to thechapter 6)

Remove the two dowel pins and cylinderhead gasket.

Remove cam chain guide and then removecylinder.

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

Cam Chain Guide

Dowel Pins

Dowel Pin

Gasket

Be careful not to drop foreign mattersinto the crankcase.

°Ø


7-14

VITALITY 50

Remove the piston pin clip.

Press the piston pin out of the piston andremove the piston.

INSPECTIONInspect the piston, piston pin and pistonrings.Remove the piston rings.

Clean carbon deposits from the piston ringgrooves.

Inspect the piston wall forwear/scratches/damage.

If any defects are found, replace the pistonwith a new one.

Install the piston rings onto the piston andmeasure the piston ring-to-groove clearance.Service Limits: Top: 0.09mm replace if over

2nd: 0.09mm replace if over

Place a clean shop towel in the crankcaseto keep the piston pin clip from fallinginto the crankcase.

°ØPiston

Clip Piston Pin

Towel

Take care not to damage or break thepiston rings during removal.

°Ø


7-15

VITALITY 50

Remove the piston rings and insert eachpiston ring into the cylinder bottom.

Measure the piston ring end gap.Service Limit: Top: 0.5mm replace if over

2nd: 0.65mm replace if overOil ring: 0.9mm replace if over

Measure the piston pin hole I.D.Service Limit: 13.04mm replace if over

Measure the piston pin O.D.Service Limit: 12.96mm replace if below

Use the piston head to push each pistonring into the cylinder.

°Ø 20mm


7-16

VITALITY 50

Measure the piston O.D.

Service Limit: 38.9mm replace if below

Measure the piston-to-piston pin clearance.Service Limit: 0.02mm replace if over

CYLINDER INSPECTIONInspect the cylinder bore for wear or damage.Measure the cylinder I.D. at three levels oftop, middle and bottom at 90° to the pistonpin (in both X and Y directions).Cylinder I.D.:Service Limit: 39.1mm replace if over

Measure the cylinder-to-piston clearance.Service Limit: 0.1mm repair or replace if

over

The true roundness is the differencebetween the values measured in X and Ydirections. The cylindricity (differencebetween the values measured at the threelevels) is subject to the maximum valuecalculated.Service Limits: True Roundness: 0.05mm repair or replace if over Cylindricity: 0.05mm repair or replace ifover

4.5mmTake measurement at 4.5mm from thebottom and 90° to the piston pin hole.

°Ø


7-17

VITALITY 50

PISTON RING INSTALLATIONInstall the piston rings onto the piston.Apply engine oil to each piston ring.

Measure the connecting rod small end I.D.Service Limit: 13.06mm replace if over

Measure the connecting rod to piston pinclearance.Service Limit: 0.06mm replace if over

Second

Side Rail

Top

Side Rail

Oil Ring

• Be careful not to damage or breakthe piston and piston rings.• All rings should be installed with

the markings facing up.• After installing the rings, they

should rotate freely without sticking.

°Ø


7-18

VITALITY 50

Inspect the exhaust side and intake sidechain guides.Wear/Damage _ Replace.

PISTON INSTALLATIONRemove any gasket material from thecrankcase surface.

Install the piston, piston pin and a newpiston pin clip.

CYLINDER INSTALLATIONInstall the dowel pins and a new cylindergasket on the crankcase.Coat the cylinder bore, piston and pistonrings with clean engine oil.Carefully lower the cylinder over the pistonby compressing the piston rings.

Intake Side Guide

Exhaust Side Guide

• Apply proper clean engine oilaround cylinder wall.• Be careful not to damage or break

the piston rings.• Stagger the ring end gaps at 120°

to the piston pin.

°Ø

Be careful not to drop foreign mattersinto the crankcase.

°Ø

• Position the piston “IN” markon the intake valve side.• Place a clean shop towel in the

crankcase to keep the piston pin clipfrom falling into the crankcase.

°Ø

“IN” Mark

sm - kymco vitality 50 - chapter 07 (2-stroke cylinder - head - valves)

Documents