Long Island Marine Surveyor

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Compression testing Boat Engines
Compression testing Boat Engines Boat Delamination Underwater Machinery Steering Station Boat Engines Boat Bilges Marine Fuel Systems Boat Fire Safety Safety equipment Electrical Oil Analysis

 

 

Compression testing outboard engines

This is a photo of an outboard engine.  Inspection would consist of an compression test of each cylinder.  Compression testing of each cylinder ensures that the engine is viable.  An accurate cylinder compression check giver a good idea of the condition of the basic working parts of the engine It is also and important first step in any tune-up, as a motor with low or unequal compression between cylinders cannot be satisfactorily tuned.  Any compression problem discovered during this check must be corrected before continuing with the tune up procedure.  

How a compression test is done.
  1. With the engine warm disconnect the spark plug wires and remove the plugs.
  2. connect the compression tester to the top spark plug hole according to manufacture's instructions.
  3. Mark sure the throttle is held wide open and crank the engine through at least 4 compression strokes.  Record the gauge readings.
  4. Repeat this for each of the remaining cylinders

While minimum cylinder compression should be not less than 100 psi, the actual readings are not as important as the differences in readings when interpreting the results.  A variation of more that 15 psi between 2 cylinders indicates a problem with the lower reading cylinder, such as sticking piston rings and or scored pistons or cylinders.  In such cases, pour a tablespoon of engine oil into the suspected cylinder and repeat pervious steps.  If the compression is raised significantly by 10 psi in and old engine the rings are worn and should be replaced.

If the power head shows signs of overheating discolored or scorched paint but the compression test turns up nothing abnormal check the cylinders visually through the transfer ports for possible scoring.  A cylinder can be slightly scored and still deliver a relatively good compression reading.  In such a case, it is also a good idea to double check the water pump operation as a possible cause for overheating.

Key Benefits

bulletA compression test is the best way to examine the internal engine without taking it apart.
bulletA engine that has poor compression will always perform poorly.
bulletA compression test is billed per engine.

 

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