Honda CG125 Valve Clearance
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Servicing
New valves will change their clearances while they run in
so check every 2500 miles,
when run in you will find they do not need adjusting so
often, so
check every 5000 miles.
It's not recommended to ignore checking the valve
clearance but if you do,
listen (helmet off) to the valves at the top of the engine
when its running, if they are excessively noisy (clatter, clatter) the clearance
is to big and needs adjustment.
If one of the valves goes quiet its clearance is to small
and must be adjusted immediately to prevent damage.
Performance drop, bad idling, problems starting or
compression drop could mean the valve clearance is to big or small, check
immediately to prevent damage.
Valve clearances normally increase due to mechanical wear,
but can sometimes decrease.
The Honda CG125 is a pushrod type so valve clearance
could reduce (but may increase), as the engine warms up.
If the valve clearance is to big the only damage you are likely to have done is
increased the wear rate of the valve.
Valves wear out (normally takes a very long time and high
mileage) and can be replaced, when
the gap is to large they wear out far quicker.
1. Leave bike overnight to cool down, this is essential
since the valve clearance changes with a hot engine.
If you do not have the two covers in the picture above (you will have something
more like
Picture), skip step 2 below and go straight
to step 3.
2. If you really can not do this step 2 then try step 4 instead.
Remove the two round covers (use 10 mm and 6 mm Allen keys, hex, 6 sided
Picture) on the left hand side of the
engine case (see picture above).
(If they will not undo, warm the bike up and then try,
once they are off leave bike overnight to cool down again).
The 10 mm one covers the nut for turning over the engine.
The 6 mm one covers the marks for valve clearance and
timing are (T is for valve and F for timing).
Turn engine over anticlockwise with a 14 mm socket (Picture) until a
small on its side T appears near the outside edge of the disc (don't mistake F
for T).
If you do not have a 14 mm socket you can use rear
wheel + 5th gear instead (wheel needs to be turning to change between gears)
(Never turn the rear wheel in the direction that would
make the bike go backwards when the bikes in gear, that would turn the engine
over in reverse)
You can remove the spark plug to make turning over the
engine easier but not really needed.
Use a torch and magnifying glass since T is very small and stamped in to the metal, do not use a house light bulb since
its to powerful and will hide it with glare.
The black outside edge in the drawing
above could be curved away from you making it invisible under the wrong light
(grey area is not curved so will be visible).
Direct sunlight or strong daylight could also make it
impossible to see(take bike in to a building with low or no daylight or at least
find as much shade as possible)
Line the mark (vertical line) below (maybe next to) the T up
with the grove at the top of the hole(only turn anticlockwise since engines
don't like going in reverse)
(if your eyesight is to bad ask someone
else).
3. Skip all of this step 3 (go to step 4) if you were able to do step 2.
If you really can not do this step 3 then try step 4 instead.
Remove the gear
change lever
Remove the entire lower left hand side engine cover (need 8
mm long and thin socket).
(if the nuts will not undo, warm the bike up and try again,
once they are off leave bike overnight to cool down again)
(if the engine cover does not come off after removing all the
nuts, tap the cover to break the seal).
If the covers gasket does not come off in one piece (due to old age) you will have to replace it
(you can smear a very small amount of light grease around it).
If the nuts and threads are suffering from corrosion you can use grease
(even better is copper grease) to stop them getting any worse.
Mark
Vertical line next to the T
Find the mark at around 12 to 1 o'clock,
Turn the engine over anti clockwise with a 17 mm socket (Picture), you may be able to use a
spanner or your hand (by hand requires the spark plug removed).
Line the vertical line next to the
T with the mark (don't mistake F
for T).
4. Skip all of this step 4 if you managed step 2 or 3.
This step is not as good as step 2 or 3 so only do this step
as a last resort.
You need to get the piston to the highest point in the
engine, this is called Top Dead Centre (TDC).
Never turn the rear wheel in the direction that would make
the bike go backwards when the bikes in gear, that would turn the engine over in
reverse.
Put the bike in to 5th gear (you will have to turn the back
wheel to change between gears).
Remove the spark plug and put something like a thin screw
driver in the hole above the piston.
Turn the back wheel and watch the piston move up and down
(make sure what you put in hole does not get trapped or damage
anything or fall in to the engine).
When the piston moves upwards it will push whatever you put
in the hole upwards, after the piston reaches Top Dead Centre (TDC) it will go
downwards.
It's essential to get the piston to the highest point
in the engine to get the correct valve clearance.
Ignore all of Step 5 if you have the
front drum brake model.
5. Valve Clearance
Step 5
6. Remove the valve cover, its on the very top of the
engine, two bolts on the right hand side and one on the left (10mm),
there's a rubber gasket inside a grove
inside the lid (do not lose or damage / trap it, if you drop it in dirt clean it
then soak in engine oil).
You will find there is a technique to
getting the valve cover off, it gets caught on the bikes metal frame and also
the valves inside.
You may think its impossible to get out,
but there is a way, keep trying all the different angles till you find the
technique, brute force does not work.
Front Disc Brake model, go to right hand
side of bike, lift valve cover up and tilt it forwards slightly, tilt cover
towards you.
7. Check that you can rock the valves, if you can not, you are on the wrong
engine stroke, simply repeat step 2 or 3 (which ever one you did).
If you can not work out if the valves
are rocking, they will only rock if there's some valve clearance.
If your on the wrong stroke there's no
valve clearance (see picture below).
Valve Screw
Valve Nut
Valve Clearance
2nd Valve
Feeler Gauge
Alternative Picture
8. The valve clearance should be set to 0.08mm (0.003
in) on both valves, this applies to all Honda CG125 models, there are only 2 valves.
A Feeler Gauge (Picture) is available from
most car motor shops, a feeler gauge is
just a set of metal plates of various thicknesses.
The valve clearance is the gap
between the round metal rods (its easy to assume its a single rod since gap is
so small).
If the valve clearance is correct,
the feeler gauge will feel very slight resistance when moving through the gap.
If you find the valves need to be
adjusted, its worth trying to turn the engine over several times (repeat step 2
or 3
twice then check and repeat)
to see if it then is
correct, there's always a slight variation every time you turn the engine over.
To adjust a valve, loosen the nut
(10mm) on the valve you
wish to adjust, use pliers (or hand) to turn the top of the screw
thread (or obtain the proper tool)
until the clearance is at the desired amount, then re tighten nut.
Recheck valve clearance after re
tightening the nut, if its gone out, loosen nut again and readjust.
If the valve clearance changes
every time you tighten the nut, you may have to hold the screw when tightening
the nut
or set the clearance slightly
wrong so when the nut is tightened the clearance becomes correct.
9. Reassemble everything in reverse order, but make sure
the rubber air hose is not trapped on the inside when
attaching air box to valve cover (does
not apply to front drum brake model since it does not have one).
Servicing
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