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:
Bleeding the hydraulic brake system
WARNINGBleed the hydraulic brake system whenever:
the system is disassembled.
a brake hose is loosened, disconnected or
replaced.
the brake fluid level is very low.
brake operation is faulty.
NOTE:
Be careful not to spill any brake fluid or allow
th ...
Faulty front fork legs
Leaking oil
- Bent, damaged or rusty inner tube
- Cracked or damaged outer tube
- Improperly installed oil seal
- Damaged oil seal lip
- Incorrect oil level (high)
- Loose damper rod assembly bolt
- Damaged damper rod assembly bolt copper
washer
- Cracked or damaged front fork cap O-ring
M ...
Checking the crankshaft position sensor
1. Disconnect:
Crankshaft position sensor coupler
(from the wire harness)
2. Check:
Crankshaft position sensor resistance
Out of specification Replace
the crankshaft
position sensor/stator assembly.
a. Connect the pocket tester ( × 100) to the
crankshaft position sensor c ...