Yamaha YXR660FAS Service Manual download pdf (Page 89)

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CHK

ADJ

MEASURING THE COMPRESSION PRESSURE

5. Remove:

• spark plug

6. Attach:

• adapter

• compression gauge 1

7. Measure:

• compression pressure

Above the maximum pressure:

Check the cylinder head, valve surfaces,

and piston crown for carbon deposits.

Below the minimum pressure:

Squirt a few drops of oil into the affected

cylinder and measure again.

Refer to the table below.

▼▼▼▼ ▼ ▼▼▼▼ ▼ ▼▼▼▼ ▼ ▼▼▼▼ ▼ ▼▼▼▼ ▼ ▼▼▼▼ ▼▼▼

a. Crank over the engine with the electric

starter (be sure the battery is fully charged)

with the throttle wide-open until the com-

pression reading on the gauge stabilizes.

Compression gauge

P/N. YU-33223, 90890-03081

Adapter

P/N. YU-33223-4, 90890-04082

Compression pressure

(with oil introduced into cylinder)

Reading Diagnosis

Higher than

without oil

Worn or damaged pis-

tons

Same as with-

out oil

Defective ring(s), valves,

cylinder head gasket or

piston is possible.

Compression pressure

(at sea level)

Standard:

1,324 kPa

(13.24 kg/cm

2

, 188.31 psi)

Minimum:

1,150 kPa

(11.5 kg/cm

2

, 163.57 psi)

Maximum:

1,480 kPa

(14.8 kg/cm

2

, 210.50 psi)

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