Re: Weird JW compression test.

[cajuncook1]

Some years back, a member by the name of Lloyd Lautner, explain a way by which compression testing should be performed in a certain manner that made a lot of sense. This explanation is not word for word but basically a summary of his explanation.

Compression should be measure when the motor is cold and dry. "Dry," meaning no extra oil or addition of oil during testing. This is to maintain testing conditions as much as possible without adding variables to influence readings. If a motor is a rope start motor then compression testing should be done using the rope start method. If a motor is a electric starter motor then compression testing should be done using the electric starter method. Electric drills should not be used in compression testing.

By using the rope start method or electric starter method helps keep evaluation of compression consistent. Different makes and types of compression gauges can influence compression readings, but that is another discussion.

Some outboard motor companies did not release acceptable compression values in their repair literature. OMC did not release compression values, but Chrysler and Mercury did…..If I am mistaken please correct me.

Since some companies did not release compression values, mechanics in the industry recorded and established what acceptable compression values were when the motors were relatively new. We now use those compression numbers to determine what is acceptable compression for these vintage and antique outboard motors.

Again, it is about maintaining consistent measuring methods for rope start motors and electric starter motors to get compression readings and comparing those to established compression readings to determine if the motor has acceptable compression values.

Cheers,

Cajun