Yamaha YZF-R125 Service Manual: Measuring the compression pressure
NOTE:
Insufficient compression pressure will result in a loss of performance.
1. Measure:
Valve clearance Out of specification →Adjust.
Refer to "ADJUSTING THE VALVE CLEARANCE" on page 3-3.
2. Start the engine, warm it up for several minutes, and then turn it off.
3. Remove:
- Rider seat
- Right upper side cowling Refer to "GENERAL CHASSIS" on page 4-1.
4. Remove:
- Fuel tank Refer to "FUEL TANK" on page 7-1.
5. Disconnect:
- Coolant temperature sensor coupler "1"
- Spark plug cap "2"
6. Remove:
- Spark plug
| CAUTION: Before removing the spark plug, use compressed air to blow away any dirt accumulated in the spark plug well to prevent it from falling into the cylinder. |
7. Install:
- Extension "1"
- Compression gauge "2"
8. Measure:
- Compression pressure
Out of specification Refer to steps (c) and
(d).
a. Set the main switch to "ON".
b. With the throttle wide open, crank the engine until the reading on the compression gauge stabilizes.
c. If the compression pressure is above the maximum specification, check the cylinder head, valve surfaces and piston crown for carbon deposits.
Carbon deposits Eliminate.
d. If the compression pressure is below the minimum specification, pour a teaspoonful of engine oil into the spark plug bore and measure again.
Refer to the following table.
9. Remove:
- Extension
- Compression gauge
10.Install:
- Spark plug
11.Connect:
- Spark plug cap
- Coolant temperature sensor coupler
12.Install:
- Fuel tank Refer to "FUEL TANK" on page 7-1.
13.Install:
- Right upper side cowling
- Rider seat Refer to "GENERAL CHASSIS" on page 4-1.
Checking the ignition timing
NOTE:
Prior to checking the ignition timing, check the
wiring connections of the entire ignition system.
Make sure all connections are tight and free of
corrosion.
1. Remove:
Rider seat
L ...
Checking the engine oil level
1. Stand the vehicle on a level surface.
NOTE:
Place the vehicle on a suitable stand.
Make sure the vehicle is upright.
2. Start the engine, warm it up for several minutes,
and then turn it ...
Other materials:
Replacing the front brake pads
NOTE:
When replacing the brake pads, it is not necessary
to disconnect the brake hose or disassemble
the brake caliper.
1. Measure:
Brake pad wear limit "a"
Out of specification Replace
the brake
pads as a set.
2. Install:
Brake pad support
Brake pad spring
Brake pads ...
Adjusting the rear disc brake
1. Check:
Brake pedal position
(distance "a" from the center of the rider footrest
to the center of the brake pedal)
Out of specification Adjust.
2. Adjust:
Brake pedal position
a. Loosen the locknut "1".
b. Remove the cotter pin "2", washer "3", and
pin "4".
c. Turn t ...
Removing the crankshaft
1. Remove:
Crankshaft "1"
NOTE:
Remove the crankshaft with the crankcase
separating tool "2".
Make sure the crankcase separating tool is
centered over the crankshaft.
CAUTION:
To protect the end of the crankshaft, place
an appropriate sized socket between the
c ...