Honda Crf250l Service Manual

							10-14
dummyhead
dummyhead
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 temperature.
To avoid burns, wear insulated gloves when handling
the heated cylinder head.
Support the cylinder head and drive out the valve
guides from the combustion chamber side of the
cylinder head.
While the cylinder head is still heated, take off a new
valve guides [1] from the freezer.
Adjust the valve guide driver to the valve guide height
and drive in the valve guide from the camshaft side.
Let the cylinder head cool to room temperature.
Ream a new valve guides.
 • Use cutting oil on the reamer during this operation.
 • Take care not to tilt or lean the reamer in the guide while reaming. Otherwise, the valves may be
installed slanted, causing oil leakage from the stem
seal and improper valve s eat contact. This may
prevent valve seat refacing
 • Insert the reamer from the combustion chamber side of the head and always rotate the reamer clockwise.
Clean the cylinder head thoroughly to remove any
metal particles after reaming and reface the valve seat
(page 10-15).
Do not use a torch
to heat the cylinder head; it may cause
warping.
TOOL:
[1] Valve guide driver 07HMD-ML00101
[1]
TOOL:
[2] Valve guide driver 07743-0020000
SPECIFIED HEIGHT:
IN/EX: 13.8  – 14.0 mm (0.54  – 0.55 in)
[2][1]
TOOL:
[1] Valve guide reamer, 4.5 mm 07HMH-ML00101
[1] 
						

							10-15
dummyhead
dummyhead
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
 • Uneven seat width:
– Bent or collapsed valve stem; Replace the valveand reface the valve seat
 • Contact area (too low or too high area):
– Reface the valve seat
REFACING
Reface the valve seat using the following tools.
 • Follow the refacer manufacturer’s operating instructions.
 • Be careful not to grind the seat more than necessary.
1. Use a 45° seat cutter, remove any roughness or irregularities from the seat.
2. Use a 32° flat cutter, re move the top 1/4 of the
existing valve seat material.
3. Use a 60° interior cutter, remove the bottom 1/4 of the existing valve seat material.
4. Using a 45° seat cutter, cut the seat to the proper
width.
5. After cutting the seat, apply lapping compound to the valve face, and lap the valve using light pressure.
 • Excessive lapping pressure may deform or damagethe seat.
 • Change the angle of lapping tool [1] frequently to
prevent uneven seat wear.
 • Do not allow lapping compound to enter the guides.
After lapping, wash any residual compound off the
cylinder head and valve and re check the seat contact.
TOOLS:
Cutter holder, 4.5 mm 07781-0010600
Seat cutter, 27.5 mm (45° EX) 07780-0010200
Seat cutter, 33 mm (45° IN) 07780-0010800
Flat cutter, 27 mm (32° EX) 07780-0013300
Flat cutter, 30 mm (32° IN) 07780-0012200
Interior cutter, 30 mm (60° EX) 07780-0014000
Interior cutter, 37.5 mm (60° IN) 07780-0014100
VALVE SEAT WIDTH:
0.90  – 0.10 mm (0.035  – 0.043 in)
[1]
Old seat width
32°
60°
Old seat width
[1] 
						

							10-16
dummyhead
dummyhead
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 SPRING
SPRING SEAT
STEM SEAL
VALVE 
GUIDE
INNER SPRING
RETAINER
EXHAUST VALVE 
SHIM
To avoid damage to the seal, turn the
valve slowly when inserting.
[2]
[3]
[1]
[2]
[3]
[1] 
						

							10-17
dummyhead
dummyhead
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 (page 4-47)
– Rocker arm (page 10-11)
INSTALLATION
Do not allow dust
and dirt to enter the crankcase.Clean any gasket material from the cylinder mating
surfaces.
Install the following:
– Dowel pins [1]
– New gasket [2]
– Cam chain guide A [3]
Route the cam chain through the cylinder head and
install the cylinder head [1] onto the cylinder.
Apply engine oil to the new cylinder head mounting nut
[2] threads and seating surface.
Install and tighten the new cylinder head mounting nuts
with new washers [3] in a cr isscross pattern in two or
three steps to the specified torque.
Install and tighten the cylinder head bolts [4] securely.
Install the following:
– Camshaft (page 10-9)
– Engine (page 15-7) TOOLS:
[3] Valve spring compressor 07757-0010000
[4] Valve spring compressor 
attachment 07959-KM30101
[3]
[1]/[2][4]
[1]
[2][3]
Be careful not to let
the cylinder head
bolts, washers and nuts fall into the
crankcase.
TORQUE: 45 N·m (4.6 kgf·m, 33 lbf·ft)
[4][1]
[2]/[3] 
						

							MEMO
dummyhead
dummyhead 
						

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

							11-2
dummyhead
dummyhead
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 before installing
cylinder.
 • Clean all disassembled parts with cleaning solvent  before inspection, use compressed air to dry the parts.
TROUBLESHOOTING
Compression too low, hard starting or poor performance at low speed
 • Leaking or damaged cylinder head gasket
 • Worn, stuck or broken piston rings
 • Worn or damaged cylinder and piston
 • Loose spark plug
Compression too high, overheating or knocking
 • Excessive carbon built-up on piston or combustion chamber
Excessive smoke
 • Faulty cylinder, piston and piston rings
 • Improper installation of piston rings
 • Scored or scratched piston or cylinder wall
Abnormal noise (piston)
 • Worn piston pin or piston pin hole
 • Worn or damaged cylinder, piston or piston ring
 • Worn connecting rod small end
COMPONENT LOCATION
4.2 N·m (0.4 kgf·m, 3.1 lbf·ft) 
						

							11-3
dummyhead
dummyhead
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
towel over thecrankcase to
prevent the piston
pin clips from falling into the crankcase.Remove the piston pin clips [1] with pliers.
Push the piston pin [1] out of the piston [2] and
connecting rod, and remove the piston.
[1]
[2][1]
[1]
[1]
[2] 
						

							11-4
dummyhead
dummyhead
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 to CYLINDER/ PISTON SPECIFICATIONS
(page 1-6).
Replace any part if it is out of service limit.
STUD BOLT REPLACEMENT
Thread two nuts onto the stud bolt [1] and tighten them
together, and use a wrench on  them to turn the stud bolt
out.
Install new stud bolts into the crankcase and tighten
them to the specified torque.
After installing the stud bolts , check that the length from
the bolt head to the crankcase surface is within
specification.
[1]
[1]
TORQUE: 9.0 N·m (0.9  kgf·m, 6.6 lbf·ft)
142.0 ± 1.0 mm 
(5.6 ± 0.04 in) 
						

							11-5
dummyhead
dummyhead
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.
Apply engine oil to the piston pin hole inner surface and
sliding surface.
When cleaning the cylinder mating
surface, place a
shop towel over the cylinder opening to
prevent dust or dirt enter the
crankcase.Clean any gasket material from the cylinder mating
surface [1] of the crankcase.
Apply molybdenum oil solution to the connecting rod
small end inner surfaces.
Apply molybdenum oil solution to the piston pin [1] outer
surfaces.
Install the piston [2] with its  IN mark [3] facing intake
side.
Install the piston pin.
Be careful not to
damage the piston
and rings.
120°
120°
120°
[2]
20 mm (0.8 in) 
OR MORE
[3]
[4]
[6]
[5]
[3]
[2]
[1]
[1]
[1]
[1]
[2][3]