| Buying Used Outboard Power: Quest for Used Engines |
From "Shipshape Boating"
episode DSSB-205 |
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A compression test should be done to check the head gasket, the piston rings and the cylinders of any used outboard engine. A compression gauge will test how many pounds per square inch each cylinder is receiving. Each cylinder should not vary more that 10 percent. Tip: This test is best performed with the motor off the boat, disconnected from the fuel line. - Remove each spark plug wire using a spark plug wrench.
- Thread in the adapter (figure A) and insert the compression gauge (figure B).
Note: you will need to purchase a compression gauge adapter that is made for your specific engine at a marine store. - Connect the motor to a battery so you will be able to turn the motor over.
- Turn the motor a full two revolutions using a starting button.
- Read the gauge, and write down the result identifying which cylinder was tested (figure C).
- Do this for each cylinder until all have been tested.
The compression of each cylinder should not deviate more than 10 percent between cylinders. If it does, a piston may need to be re-built or the head gasket replaced which can be expensive.
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