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"

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 rear wheel
    1. Check: Rear wheel axle Rear wheel Wheel bearings Oil seals Refer to "CHECKING THE FRONT WHEEL" on page 4-8. 2. Check: Tire Rear wheel Damage/wear → Replace. Refer to "CHECKING THE TIRES" on page 3-23 and "CHECKING THE WHEELS" on page 3-25. 3. Measure: Radi ...

    Checking the condition of the bulbs
    The following procedure applies to all of the bulbs. 1. Remove: Bulb WARNINGSince the headlight bulbs get extremely hot, keep flammable products and your hands away from them until they have cooled down. CAUTION: Be sure to hold the socket firmly when re ...

    Avoid Carbon Monoxide Poisoning
    All engine exhaust contains carbon monoxide, a deadly gas. Breathing carbon monoxide can cause headaches, dizziness, drowsiness, nausea, confusion, and eventually death. Carbon Monoxide is a colorless, odorless, tasteless gas which may be present even if you do not see or smell any en ...

    2026 Copyright www.yam-r125.net |