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8. CYLINDER/PISTON AGILITY 50
8
1.0kg-m
8
Do not bend
8-0
8. CYLINDER/PISTON AGILITY 50
SERVICE INFORMATION.......................8-1 PISTON REMOVAL................................. 8-2
TROUBLESHOOTING..............................8-1 PISTON INSTALLATION........................ 8-6
CYLINDER REMOVAL ...........................8-2 CYLINDER INSTALLATION ................. 8-6
SERVICE INFORMATION
GENERAL INSTRUCTIONS
· The cylinder and piston can be serviced with the engine installed in the frame.
· After disassembly, clean the removed parts and dry them with compressed air before inspection.
SPECIFICATIONS
Item Standard (mm) Service Limit (mm)
I.D. 50.00-50.01
Warpage 0.05
Cylinder
Cylindricity 0.05
True roundness 0.05
Ring-to- Top 0.015-0.050 0.09
clearance Second 0.015-0.050 0.09
Top 0.08-0.20 0.45
Piston, Ring end gap Second 0.05-0.20 0.45
piston ring Oil side rail 0.20-0.70
Piston O.D. 49.97-49.990 49.9
Piston O.D. measuring 9mm from bottom of skirt
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 12.994-13.000 12.96
Piston-to-piston pin clearance 0.002-0.014
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
8-1
8. CYLINDER/PISTON AGILITY 50
Cylinder
CYLINDER REMOVAL
Remove the cylinder head. ( 7-6)
Remove the cam chain guide.
Remove the cylinder.
Dowel Pins
Remove the cylinder gasket and dowel pins.
Clean any gasket material from the cylinder
surface.
Gasket
Piston Pin
PISTON REMOVAL
Remove the piston pin clip.
Place a clean shop towel in the crankcase
to keep the piston pin clip from falling
into the crankcase.
Press the piston pin out of the piston and
remove the piston.
Piston Rings Piston
8-2
8. CYLINDER/PISTON AGILITY 50
Inspect the piston, piston pin and piston rings.
Remove the piston rings.
Take care not to damage or break the
piston rings during removal.
Clean carbon deposits from the piston ring
grooves.
Install the piston rings onto the piston and
measure the piston ring-to-groove clearance.
Service Limits: Top: 0.09mm replace if over
2nd: 0.09mm replace if over
Remove the piston rings and insert each
piston ring into the cylinder bottom.
Use the piston head to push each piston
ring into the cylinder.
Measure the piston ring end gap.
Service Limit: 0.45mm replace if over
Measure the piston pin hole I.D.
Service Limit: 13.04mm replace if below
8-3
8. CYLINDER/PISTON AGILITY 50
Measure the piston pin O.D.
Service Limit:12.96mm replace if below
Measure the piston O.D.
Take measurement at 9mm from the
bottom and 90° to the piston pin hole.
Service Limit: 38.9mm replace if below
Measure the piston-to-piston pin clearance.
Service Limit: 0.02mm replace if over
CYLINDER INSPECTION
Inspect the cylinder bore for wear or damage.
Measure the cylinder I.D. at three levels of
top, middle and bottom at 90° to the piston
pin (in both X and Y directions).
Service Limit: 39.10mm repair or replace if
over
Measure the cylinder-to-piston clearance.
Service Limit: 0.1mm repair or replace if
over
The true roundness is the difference between
the values measured in X and Y directions.
The cylindricity (difference between the
values measured at the three levels) is subject
to the maximum value calculated. Top
Service Limits:
True Roundness: 0.05mm repair or replace Middle
if over
Cylindricity: 0.05mm repair or replace if over
Bottom
8-4
8. CYLINDER/PISTON AGILITY 50
Inspect the top of the cylinder for warpage.
Service Limit: 0.05mm repair or replace if over
Measure the connecting rod small end I.D.
Service Limit: 13.06mm replace if over
PISTON RING INSTALLATION
Install the piston rings onto the piston.
Apply engine oil to each piston ring.
· Be careful not to damage or break the
piston and piston rings.
· All rings should be installed with the Top
markings facing up.
· After installing the rings, they should Second
rotate freely without sticking. Side Rail
Expander
Side Rail
Top
Second
Oil
8-5
8. CYLINDER/PISTON AGILITY 50
PISTON INSTALLATION
Remove any gasket material from the
crankcase surface.
Be careful not to drop foreign matters
into the crankcase.
Piston Pin Clip
Install the piston, piston pin and a new piston
pin clip.
· Position the piston "IN" mark on the
intake valve side.
· Place a clean shop towel in the
crankcase to keep the piston pin clip
from falling into the crankcase.
Piston Pin Piston
Dowel Pins
CYLINDER INSTALLATION
Install the dowel pins and a new cylinder
gasket on the crankcase.
Gasket
Cylinder
Coat the cylinder bore, piston and piston
rings with clean engine oil.
Carefully lower the cylinder over the piston
by compressing the piston rings.
· Be careful not to damage or break the
piston rings.
· Do not align the ring end gaps with the
intake/exhaust valve and piston pin.
8-6
8. CYLINDER/PISTON AGILITY 50
Install the cam chain guide.
Insert the tab on the cam chain guide into
the cylinder groove.
Install the cylinder head. ( 7-8)
Loosely install the cylinder base bolts.
Cam Chain Guide
Tighten the cylinder base bolts.
Cylinder Base Bolts
8-7