Testing Engine Compression - Westerbeke 6.5 MCG Service Manual

TESTING THE ENGINE COMPRESSION
BY-PASSING THE ECU
DESCRIPTION
The ECU is by-passed·by attaching an electrical jumper
dirnctly to the starter motor solenoid as illustrated below.
The electrical jumper can easily be assembled using a push
button and connecting wires as shown.
COMPRESSION TEST PROCEDURES
NOTE:
The activation of the starter motor is a function of
the ECU (Electronic Control Unit). To by-pass the ECU, a
simple electrical jumper arrangement can be fabricated to
connect between the battery B+ cable connection on the
starter solenoid and the spade type activation connection on
the starter solenoid with a push button in this jumper to make
a circuit between these two connections and activate the
starter solenoid.
1. Start the engine and allow it to warm up to its normal
operating temperature. Then shut it down.
2. Open the DC breaker on the unit's control box to disable
the ECU. Connect the jumper arrangement on the starter
solenoid connections.
3. Close the unit's raw water thru-hull opening. This is to
prevent the raw water pump from pumping water into the
unit's exhaust system during the test as no or very little
exhaust pressure will be present during the test to help
expel water from the unit's exhaust system during engine
cranking.
4.
Remove the high tension leds from the spark plugs and
remove all spark plugs.
5. Thread the compression gauge adapter into the spark
plug opening of cylinder
#1.
Connect the compression
gauge to the adapter.
ATTACHING THE ELECTRICAL JUMPER
6.
Activate the starter motor using the push button on the
electrical jumper arrangement for the starter. Allow the
engine to crank, observing the compression gauge. Allow
the engine to crank until the gauge reaches a maximum
reading where further cranking does not produce a higher
reading on the compression gauge. Stop cranking and
record the pressure.
7. Remove the compression gauge and adapter from the #1
spark plug opening and install it in the #2 cylinder spark
plug opening and repeat step -.·6.
8.
Proceed to the next cylinder and repeat step #6 until
all
cylinders have been tested and there
p~sures
recorded.
STANDARD COMPRESSION PRESSURE AT 400 RPM
178 PSI (12.5 KG/CM'
LOWER LIMIT· 137 PSI (9.6 KG/CM')
NOTE: A wet test can be pelformed on cylinders with "zow
compression figures. This will help determine
if
the iow ·
compression is the result of worn cylinders/rings or worn
valve seats/valves or both. Place a few squirts of oil into
the cylinder and the peiform the compression test on that
cylinder.
a.
A dramatic rise in recorded compression value would
iridicate worn cylinder/rings.
b. A minimal rise in recorded compression value
would indicate both cylinder/ring and valve wear.
c. No appreciable rise in recorded compression would
indicate valve/valve seat wear.
Engines
&
Generators
3