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:

    Cleaning and lubricating the drive chain
    The drive chain must be cleaned and lubricated at the intervals specified in the periodic maintenance and lubrication chart, otherwise it will quickly wear out, especially when riding in dusty or wet areas. Service the drive chain as follows. NOTICE The drive chain must be lubricated ...

    Assembling the crankcase
    1. Thoroughly clean all the gasket mating surfaces and crankcase mating surfaces. 2. Apply: Sealant (onto the crankcase mating surfaces) NOTE: Do not allow any sealant to come into contact with the oil gallery. 3. Install: Right crankcase NOTE: Turn the shift drum segment ...

    Checking the cylinder head
    1. Eliminate: Combustion chamber carbon deposits (with a rounded scraper) NOTE: Do not use a sharp instrument to avoid damaging or scratching: Spark plug bore threads Valve seats 2. Check: Cylinder head Damage/scratches   Replace. Cylinder head water jacket Min ...

    2026 Copyright www.yam-r125.net |