Compresion Test

[dunc333]

hi guys if doing a compression test on a outboard and motor doesn't run will test be as acurte when motor cold to motor warmed up and what would you allow for diff in cold and warm motor cheers and thanks in advance for your thoughts.

[Bruce the Postie]

Do Both and split the difference.

Cheers,

Bruce

[IWANNABROCK]

Do a dry test first, then put couple of drops engine oil in cylinders, then retest, compression should be higher on wet test, if 2 strokes have low comp when cold, then it will be very hard to start as wont be able to scavenge the fuel. try a squirt of aerostart if low comp. will help to fire.

[a boat]

Hi, the proper way is with the engine hot, good battery, all plugs out and throttle all the way open. Also a leak down test should be done to confirm condition of the bores. Many times the compression test will be fine but a leak down test will highlight a problem.

As long as the compressions are even that is the main thing.

Cheers,

Huey.

[stoney]

As the others have said only thing is that there is no need to have the throttle wide open.

Makes no difference at all.

[Gribble]

As the others have said only thing is that there is no need to have the throttle wide open.

Makes no difference at all.

It will make a difference WOT or Closed because there will be a difference in manifold pressure between the two, even at slow cranking speeds. However the most important thing is that you test each cylinder consistently, count the number of compression cycles and test at least 3 times before moving to the next cylender and use either wide open or idle for all of them.

Or if your in possession of one.....

RTFM!