Yamaha YZF-R125 Service Manual: Measuring the compression pressure

Yamaha YZF-R125 Service Manual / Periodic checks and adjustments / Engine / 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"

Measuring the compression pressure

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"

Measuring the compression pressure

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:

Checking the oil pump
1. Check: Oil pump drive gear Oil pump driven gear Oil pump housing Oil pump housing cover Cracks/damage/wear Replace the defective part(s). 2. Measure: Inner-rotor-to-outer-rotor-tip clearance "a" Outer-rotor-to-oil-pump-housing clearance "b" - Oil-pump-housing-to-inn ...

Changing the coolant
1. Remove: Lower side cowlings Refer to "GENERAL CHASSIS" on page 4-1. 2. Remove: Radiator cap "1" WARNINGA hot radiator is under pressure. Therefore, do not remove the radiator cap when the engine is hot. Scalding hot fluid and steam may be blown out, which c ...

Installing the rear wheel (disc)
1. Install: Rear brake disc NOTE: Tighten the brake disc bolts in stages and in a crisscross pattern. 2. Check: Rear brake disc Refer to "CHECKING THE REAR BRAKE DISC" on page 4-33. 3. Lubricate: Rear wheel axle Contact surface of rear wheel hub and rear wheel Whee ...