The "other" compression test

[PT20J]

Besides the usual leak down compression test, there is the automotive style test where you put a gauge on the cylinder and run the starter a few cycles and record the maximum pressure. At the Lycoming factory class, it was said that this test is a useful measurement of the cylinder condition. The leak down test only measures leakage through the valves, and rings at TDC. But the automotive style test gives an indication of the condition of the cylinder walls since the rings won't seal as well resulting in lower pressure if the walls are worn. The example given for an IO-360 was that a new engine will be 155 psi or greater, decreasing to 140 at midlife.  A worn out cylinder will read below 120 psi. I measured mine and got between 160 and 170 on a 500 hr. factory rebuilt engine.

[EricJ]

What gauges did you use?

 

[PT20J]

23 minutes ago, EricJ said:

What gauges did you use?

 

https://www.amazon.com/dp/B09XXNN2TD?psc=1&ref=ppx_yo2ov_dt_b_product_details

[Yetti]

"Condition of the cylinder walls"  Which devolves into a discussion about do the rings or the cylinder wall create compression.   Looks like you are an over achiever already.   Atta Boy.

[A64Pilot]

Of course be sure the throttle is wide open or you will get low readings, and you will want to short out the mags, remove all plug wires or something.