Power Unit; Checking The Compression Pressure - Yamaha 55DEHD Service Manual

POWR

Power unit

Checking the compression pressure

1. Start the engine, warm it up for 5 min-
utes, and then turn it off.
2. Remove the lock plate from the engine
stop lanyard switch.
3. Remove the all spark plug caps and all
spark plugs, and then install the special
service tool 1 into a spark plug hole.
1
cC
Before removing the spark plugs, blow
compressed air in the spark plug well to
clear out any dirt or dust that may fall into
the cylinder.
Compression gauge 1:
90890-03160
4. Fully open the throttle, and then crank the
engine until the reading on the compres-
sion gauge stabilizes.
NOTE:
9 Disconnect the throttle cable joint from the
throttle control lever, and then place hold
the lever in the fully-opened position of the
throttle (ED, ET).
9 Do not pull the choke knob when checking
the compression pressure.
9 Make a note of each cylinder measurement
numeral 3 times to find the compression
average.
5-1
Power unit
68850010
Minimum compression pressure
(reference data):
55D, 75A:
340 kPa (3.4 kgf/cm
85A:
410 kPa (4.1 kgf/cm
5. If the compression pressure is below
specification and the compression pres-
sure for each cylinder is unbalanced, add
a small amount of engine oil to the cylin-
ders, and then check the compression
pressure again.
NOTE:
9 If the compression pressure increases,
check the pistons and piston rings. Replace
if worn.
9 If the compression pressure does not
increase, check the cylinder head gasket
and cylinder head. Replace if necessary.
, 49 psi)
2
2 , 59 psi)
6885J11