Yamaha YZF-R125 Service Manual: Checking the cylinder head

Yamaha YZF-R125 Service Manual / Engine / Cylinder head / 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

Checking the cylinder head

2. Check:

Cylinder head Damage/scratches Replace.

Cylinder head water jacket Mineral deposits/rust
Eliminate.

3. Measure:

Cylinder head warpage Out of specification Resurface
the cylinder head.

a. Place a straightedge "1" and a thickness gauge "2" across the cylinder head.

Checking the cylinder head

b. Measure the warpage.

c. If the limit is exceeded, resurface the cylinder head as follows.

d. Place a 400-600 grit wet sandpaper on the surface plate and resurface the cylinder head using a figure-eight sanding pattern.

NOTE:

To ensure an even surface, rotate the cylinder head several times.

Removing the cylinder head

1. Align: "I" mark "a" on the generator rotor (with the stationary pointer "b" on the generator cover) a. Turn the crankshaft counterclockwise. b. When the piston is at TDC on the compre ...

Checking the camshaft sprocket and timing chain guide

1. Check: Camshaft sprocket More than 1/4 tooth wear "a" Replace the camshaft sprocket, timing chain and crankshaft as a set. a. 1/4 tooth b. Correct 1. Timing chain roller 2. C ...

Other materials:

Incorrect engine idling speed
Engine 1. Cylinder and cylinder head Incorrect valve clearance Damaged valve train components 2. Air filter Clogged air filter element Fuel system 1. Throttle body Damaged or loose throttle body joint Improperly adjusted engine idling speed (idle adjusting screw) Improper ...

Checking the front brake lever free play
Checking the front brake lever free play Brake lever free play The brake lever free play should measure 2.0-5.0 mm (0.08-0.20 in) as shown. Periodically check the brake lever free play and, if necessary, have a Yamaha dealer check the brake system. WARNING An incorrect brake le ...

Checking the spark plug
1. Remove: Right side cover Refer to "GENERAL CHASSIS" on page 4-1. 2. Disconnect: Spark plug cap 3. Remove: Spark plug CAUTION:Before removing the spark plug, blow away any dirt accumulated in the spark plug well with compressed air to prevent it from falling ...