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:
Assembling the water pump
1. Install:
Water pump seal "1"
(into the water pump housing "2")
CAUTION:Never lubricate the water pump seal
surface
with oil or grease.
NOTE:
Install the water pump seal with the special
tools.
Install the water pump seal with the special
tools to the specifi ...
Installing the relay arm
1. Lubricate:
Spacers
Bearings
Oil seals
Bolts (unthreaded shaft portion only)
2. Install:
Bearing "1"
(to the relay arm)
Oil seal "2"
(to the relay arm)
3. Rear shock absorber assembly
4. Relay arm
5. Connecting arm
A. Left side
B. Right side ...
Checking the speed sensor
1. Check:
Speed sensor output voltage
Out of specification → Replace.
a. Connect the pocket tester (DC 20 V) to the
speed sensor coupler (wire harness end) as
shown.
Positive tester probe
gray "1"
Negative tester probe
gray/black "2"
b. Set the main switch to "ON".
c. ...