Honda Crf250l Service Manual

10-14
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CYLINDER HEAD/VALVESVALVE GUIDE REPLACEMENT
Refinish the valve seats whenever the valve guides are
replaced to prevent uneven seating.
Chill new valve guides in a freezer section of
refrigerator for about an hour.
Heat the cylinder head to 130 – 140°C (266 – 284°F)
with a hot plate or oven. Do not heat the cylinder head
beyond 150°C (302°F). Use temperature indicator
sticks, available from weld ing supply stores, to be sure
the cylinder head is heated  to the proper...

10-15
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CYLINDER HEAD/VALVES
VALVE SEAT INSPECTION/REFACING
INSPECTION
Clean the intake and exhaust  valves thoroughly to
remove carbon deposits.
Apply a light coat of Prussian Blue to the valve seats.
Tap the valve against the valv e seat several times using
a hand-lapping tool [1], without rotating the valve to
make a clear pattern.
Remove the valve and ins pect the valve seat face
width.
Inspect the valve seat face for:
 • Damaged face: – Replace the valve and reface the valve seat...

10-16
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CYLINDER HEAD/VALVESASSEMBLY
Clean the cylinder head assembly with solvent and
blow through all oil passages with compressed air.
Install the spring seats [1]  and new valve stem seals [2].
Apply molybdenum oil solution to each valve stem
sliding surface.
Insert the intake and exhaust valves [3] into the valve
guides.
Install the inner valve spring [1] and outer valve spring
[2] with the tightly wound coils should facing the
combustion chamber [3].
INTAKE VALVE 
COTTERS
OUTER...

10-17
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CYLINDER HEAD/VALVES
Grease the cotters
to ease installation.
To prevent loss of tension, do not
compress the valve
spring more than necessary.Install the spring retainer [1].
Compress the valve spring using the special tools and
install the valve cotters [2].
Support the cylinderhead above the
work bench surface
to prevent valve damage.Tap the valve stems gently with two plastic hammer to
firmly seat the cotters firmly.
Install the following:
– Spark plug (page 3-5)
–O
2 sensor...

MEMO
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11-1
11
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11. CYLINDER/PISTON
SERVICE INFORMATION ···························11-2
TROUBLESHOOTING·································11-2
COMPONENT LOCATION ··························11-2CYLINDER/PISTON ···································· 11-3
CAM CHAIN TENSIONER ·························· 11-7 

11-2
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CYLINDER/PISTON
CYLINDER/PISTONSERVICE INFORMATION
GENERAL
 • This section covers maintenance of the cylinder and piston. To service these parts, the engine must be removed from the frame.
 • Take care not to damage the cylinder wall and piston.
 • Be careful not to damage the mating surfaces when removing  the cylinder. Do not tap the cylinder too hard during removal.
 • Camshaft and rocker arm lubricating oil is  fed through an oil passage in the cylinder. Clean the oil passage...

11-3
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CYLINDER/PISTON
CYLINDER/PISTON
CYLINDER REMOVAL
Remove the following:
– Water pipe (page 9-13)
– Cylinder head (page 10-13)
Lift the cylinder [1] and remove it, being careful not to
damage the piston with the stud bolts.
 • Attach a piece of wire to the cam chain to prevent it from falling into the crankcase.
 • Do not tap the cylinder too hard and do not damage the mating surface with a screwdriver.
Remove the dowel pins  [1] and gasket [2].
PISTON REMOVAL
Place a clean shop...

11-4
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CYLINDER/PISTON
Spread each piston ring [1] and remove it by lifting up a
point opposite the gap.
 • Do not damage the piston ring by spreading theends too far.
 • Be careful not to damage the piston when removing the piston ring.
INSPECTION
Inspect the following parts for scratch, damage,
abnormal wear, deformation, burning or clogs in oil
passages.
– Cylinder
–Piston
– Piston rings
– Piston pin
– Connecting rod small end
Measure each part and calculate the clearance
according...

11-5
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CYLINDER/PISTON
PISTON INSTALLATION
Apply engine oil to the piston ring grooves.
Apply engine oil to the piston ring entire surface.
Carefully install the piston rings into the piston ring
grooves with the markings [1] facing up.
 • Do not confuse the top ring [2] and second ring [3].
 • To install the oil ring [4],  install the spacer [5] first,
then install the side rails [6].
Stagger the piston ring end gaps 120° apart from each
other.
Stagger the side rail end gaps as shown....