Compression Check - Mercury 200 OptiMax Jet Drive Service Manual

General Information
d. Add approximately 30 ml (1 oz) of engine oil into each spark plug hole. Rotate the flywheel manually several times to
distribute the oil in the cylinders. Install the spark plugs.
7. Drain the water from the oil injection system as follows:
a. Remove the remote oil hose (black without blue stripe) from the pulse fitting on the starboard side of the engine.
b. Drain any water from the hose and connect.
c. If water was present in the hose, check for water in the remote oil tank. Drain the tank if water is present.
8. Disassemble the engine starter motor and dry components.
9. Prime the oil injection pump as follows:
IMPORTANT: Fill the engine fuel system with fuel before priming the oil injection pump to prevent damage to the fuel pump
during the priming process.
a. Connect the fuel hose to the fuel lift pump.
b. Use the Method 2 - Computer Diagnostic System Oil Pump Prime procedure. This method should be used when
the break‑in clock does not need to be reset. Follow the procedures in the computer diagnostic system for priming the
oil pump. Refer to Section 3C - Priming the Oil Injection Pump.
a
NOTE: Audible click from the oil pump will tell you the pump is priming. It may take a few minutes for the pump to complete
the priming process.
10. Attempt to start the engine, using a fresh fuel source. If the engine starts, it should be run for at least one hour to eliminate
any water in the engine.
11. If the engine fails to start, determine the cause (fuel, electrical, or mechanical).

Compression Check

1. Remove spark plugs.
2. Install compression gauge in spark plug hole.
3. Hold throttle plate at WOT.
4. Pull on the recoil rope or crank the engine over until the compression reading peaks on the gauge. Record the reading.
5. Check and record compression of each cylinder. The highest and lowest reading recorded should not differ by more than
15%. A reading below 827.4 kPa (120 psi) might indicate a total engine wear problem. The following chart, is not a
representation of compression values specific to the engine that is actually tested. It is only an example.
Condition
Good
Bad
6. To find the maximum allowable minimum compression reading difference, use this formula; highest compression reading x
0.85 = the lowest allowable difference. 1241 kPa x 0.85 = 1054.85 kPa (180 x 0.85 = 153 psi).
7. Compression check is important because an engine with low or uneven compression cannot be tuned successfully to give
peak performance. It is essential, therefore, that improper compression be corrected before proceeding with an engine
tune‑up.
8. Cylinder scoring: If powerhead shows any indication of overheating, such as discolored or scorched paint, visually inspect
cylinders for scoring or other damage as outlined in Section 4 - Powerhead.
Page 1C-14
Compression Test Differences
Maximum Reading
1241 kPa (180 psi)
1172 kPa (170 psi)
a - Fuel hose to fuel lift
pump
46112
Minimum Reading
1062 kPa (154 psi)
972.2 kPa (141 psi)
90-8M0050731 MAY 2011