Compression tester question

[jabcb]

Had a mechanic/friend do a compression test on one of my bikes.
He squirted a little two stroke oil down the spark plug hole before doing the test. Got around 140 psi on both cylinders. I asked & he said that's what they taught at mechanics school.

For these old two strokes, should the test be done with, or without, the squirt of oil? Or perhaps both?
And why?

[mike1161]

I would be pretty interested in seeing it done both ways, to compare the differences in PSI readings. You would really think that adding the bit of oil would make it seal better.... Maybe someone here has done it both ways & has the results?

[jabcb]

I wasn't paying too much attention to what he was doing.
Was putting the bike away for winter.

He also said something about installing new rings in the spring.
Have never had the heads off, so the condition of the cylinders & pistons is unknown.

[tz375]

Adding oil is what you do if initial tests are low. If the numbers now rise, the rings are leaking and the small amount of oil is helping them seal while you conduct the test. Add much more oil and all you do is to raise the compression and get false readings.

I would guess that the logic was that a cold dry motor has no oil to seal the rings and will read lower than a warm running motor. That's why the correct procedure is to warm the motor first to adjust the pistons and bores to heat and bring them up to running clearances. That also makes sure the bores are lubed correctly.

If the motor won't run and Comp test is diagnostic, adding a tiny amount of oil makes sense.