How to Test a Boat Motor

Testing an outboard ashore requires a tank or an attachment.

The only outboard motor test that you can perform ashore is a compression test. The rest of the many conventional tests for an outboard must be performed with the motor under a load -- in the water, under way. Normally, you should do a compression test before you tune the motor; if the motor fails a compression test, it will require further testing and may require extensive work. There are two methods to test an outboard ashore.

Things You'll Need

• Piece of wood
• Pliers or locking pliers
• 1 1/16-inch box end wrench
• Garden hose
• Marine flushing attachment
• Plug wrench
• Compression gauge

Instructions

Garden Hose Water Supply

1. Jam a piece of wood between the blades of the motor's propeller and one of the surfaces of the motor's lower unit. Locate and remove the cotter pin that anchors the propeller nut -- a pair of pliers or locking pliers will work best for this part of the effort.

2. Set a 1 1/16-inch box end wrench on the propeller nut and turn the nut counterclockwise to remove it. With the nut removed, pull the propeller and any washers or spacers from the propeller tail-shaft.

3. Connect a garden hose to a cold-water connection close enough to the motor that the hose will reach the outboard motor. Carry the hose to the motor.

4. Unlatch and remove the motor's top cowling, if the motor is equipped with a direct hose connection. Screw the hose into the hose connection. If the motor does not have a direct hose connection, screw the hose's male connector into the female connector of a motor flushing attachment. Place the pads of the motor flushing attachment over the cooling water inlets on either side of the motor's lower unit.

5. Turn on the water supply, and open the valve until it will open no more and the water is flowing at full force. Start the motor and make such tests as are appropriate.

Test Tank

1. Insert the plug in the motor test tank. Use a shop crane to lift the outboard from its stand. Move the stand to the test tank. Lower the motor into the test tank so that you can attach the motor's mounting bracket to the tank wall.

2. Connect a garden hose to a water source. Connect the hose to the tank filler or simply put the hose in the tank. Fill the test tank sufficiently to fully submerge the cooling water inlets on the motor's lower unit in the water.

3. Start the motor and make such tests as you wish. Remove the motor from the tank with the shop crane and return it to its motor storage stand.

Compression Test

1. Take the spark plugs out of the powerhead with a plug wrench and ground the plug wires to the powerhead.

2. Thread the compression gauge into the plug bore of the Number 1 spark plug. Press the reset button on the compression gauge to return it to "0." Crank the motor -- it won't start; you're simply turning the motor over, to raise the compression in the cylinder that you're testing -- four times. Read the gauge, record the reading and reset the gauge each time.

3. Move the compression gauge to the next cylinder and repeat the process, recording the readings for each attempted cranking.

4. Compare the readings from each cylinder. The compression between the cylinders will vary, but with no more than a 15-percent variance between all of the cylinders. If any one cylinder varies more than 15 percent from every other cylinder, take the motor to your dealer: you probably have a cracked cylinder.

Tips & Warnings

• Note that, if you conduct the tests in a motor test tub, it is not necessary to remove the propeller. Propeller removal is to prevent injuries from a propeller moving at speed, not in the water.

• Regardless of the method used, stand the motor straight up when it's stored, to allow the water to drain properly.

• Disconnect the negative cable of your battery before performing any maintenance work on your outboard motor, to prevent electrical shock or accidental starting. Remove the nut from the negative post with a 5/16-inch box-end wrench. Lift the cable from your battery, move it outside of the battery box and close the lid of the battery box.

References

• "Evinrude Repair Manual - 2.5 to 250 HP Models, 2002-2007"; Seloc Marine; 2007