wrote:

I'm pretty sure where the prop stops doesn't measure anything.
How do you know it stopped in the same place "horizontally"
each time?

Because I've been watching it carefully for 3 years.

A prop that stops in an unusual position can indicate a cylinder with poor
compression, as I discovered when I had cylinder trouble 3 years ago.

There are at least two possibilities.

Why would the prop stop in a preferential position anyway?
Seems like it would be on any one of the 4 compression strokes.

Becaues of the crankshaft geometry of the horizonally-opposed Lyc. O-360,
the prop will stop in the same compass position every time as it bounces
back from the last TDC.

I'm also convinced that even the differential compression
check doesn't show what you really want to know.
The rings are AC coupled, tho less so in the Lycomings.

?

So I'd guess one would need something worse to worry
about. Maybe price of gas or user fees!

No. Something has changed, and that's something to worry about.

--
Dan
C172RG at BFM