Power Unit; Measuring The Compression Pressure - Yamaha EK25BMH Service Manual

CHK

POWER UNIT

ADJ
1
POWER UNIT
MEASURING THE COMPRESSION
PRESSURE
NOTE:
The engine should be warmed up before
measuring the compression pressure. Cor-
rect measurement cannot be obtained
when the engine is cold.
1. Measure:
•
2
Measuring steps
(1) Remove the spark plug
CAUTION:
Before removing the spark plug, clean the
spark plug well arec to prevent any dirt
from falling into the cylinder that is being
checked.
(2) Install the compression gauge
the spark plug hole.
(3) Fully open the throttle.
(4) Fully open the choke. (Make the choke
valve ineffective.)
(5) Crank the engine by means of recoil
starter (MH model) or starter motor (W,
WC, and WH models) until the com-
pression gauge gives stable reading.
(6) Remove the compression gauge
(7) Install the spark plug
3-18
Compression pressure
Below minimum compression pres-
sure → Check or replace piston, pis-
ton rings, cylinder head, and cylinder
head gasket.
Compression pressure
(reference value)
#1: 680 kPa (6.8 kgf/cm
#2: 730 kPa (7 .3 kgf/cm
Minimum compression pressure
#1: 540 kPa (5.4 kgf/cm
#2: 580 kPa (5.8 kgf/cm
Compression gauge
90890-03160
Spark plug
25 N m (2.5 kgf m, 18 ft
• •
E
2
, 98.6 psi)
2
, 105.9 psi)
2
, 78.3 psi)
2
, 84.1 psi)
1
.
2
into
2
.
1
.
lb)
•