Cylinder/Piston Service Information; Cylinder/Piston Troubleshooting - Honda 2010 CRF250R Service Manual

SERVICE INFORMATION
GENERAL
CYLINDER/PISTON
This section covers maintenance of the cylinder and piston. These procedures can be done with the engine installed in the
frame.
Before disassembly. clean the engine thoroughly to prevent dirt from entering it.
Be careful not to damage the mating surfaces when removing the cylinder. For example , do not use a screwdriver to pry the
cylinder.
Clean all disassembled parts with cleaning solvent before inspection, use compressed air to dry the parts.
Under racing conditions, the piston. piston pin and piston rings should be replaced after every 6 races or about 15 hours of
operation.
SPECIFICATIONS
Unit: mm (in)
Cylinder
ITEM
==+
STANDARD SERVICE LIMIT
LD. 76.800 76.815 (3.0236 - 3.0242)
-f
76.825 (3.0246)
Out-of-round
0.010 (0.0004)
Taper 0.010 (0.0004)
Warpage
0.05 (0.002)
Piston mark direction
---~"~O'"" ~m~a~'k~'~a~c~; n ~g·to~w ~ a~'~d~t'he"";n"ta~k~e ~ s~;Oide:o--f-I
-
~
Piston , piston
ring
Piston
0.0.
~~:;:::;;:;:::===;7~6~7~70~~76~.7~8~O~(3~.g02~2~ 4 ~3~.O~2~28~)t::::::::tl
::2i76[770 4 i O
O'((3;'a'0221t]3[)
~:
Piston
0.0. meas~",~e~m~e~n~t~p~o~;n~t
_ _ _
--c7.i'0~(~O~.2~8~) ~"~om"'t~h~e~b~O~"O~m"'-C0~'is~k;~n,,--~__.""'"'"'=._--j
Piston pin bore 1.0. 16.002 16.008 (0.6300 0.6302) 16.03 (0 .631)
Piston pin 0.0. 15.994 16.000 (0.6297 0.6299) 15.98 (0.629)
Piston-to-piston pin clearance
0.002 - 0.014 (0.0001 - 0.0006) 0.04 (0.002)
Top ring mark _ _
--1_ "~ R ~N
... M·
mark side facing up
Piston ring- to-ring
groove clearance
Piston ring end gap
Cylinder-to piston clearance
Connecting rod small end 1.0.
Connecting rod to-piston pin clearance
TROUBLESHOOTING
TOp
Top ring
Oil ring
(side rail)
0.035 - 0.065 (0.0014 - 0.0026)
0.15 - 0.25 (0.006 - 0.010)
0.20 - 0.70 (0.008 - 0.028)
0.020 0.045 (0.0008 0.0018)
16.016 16.034 (0.6305 0.6313)
I
0.016 - 0.040(0.0006-0.0017)
0.08 (0.003)
0.39 (0.015)
t
0.90 (0.035)
0.085 (0.0033)
I 16.04 (0.631)
0.06 (0.002)
Engine top-end problems usually affect engine performance. These problems can be diagnosed by a compression test o r by
tracing engine noise to the top-end with a sounding rod stethoscope.
If the performance is poor at low speeds, check for white smoke in the crankcase and cylinder head breather hose. If the hose is
smoky, check for a seized piston rings.
CompreSSion too low, hard starting or poor performance at low speeds
Leaking or damaged cylinder head gasket
Worn, stuck or broken piston rings
• Worn or damaged cylinder and piston
• Loose spark plug
Compression too high, over-heating or knocking
• Excessive carbon build-up on piston head or combustion chamber
Abnormal noise
Worn cylinder and piston
Worn piston pin or piston pin hole
• Worn connecting rod small end
• Worn connecting rod big end bearing (page
12-24)
Excessive smoke
Faulty cylinder, piston and piston rings
Improper installation of piston rings
• Scored or scratched piston or cylinder wall
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