Gene Kearns wrote in
:

Now their latest approach (almost certainly to stave off
a class action suit) is just to continually lower the limits on an
"airworthy" cylinder. It's now so low (26/80 with air leaking past
the rings and valves, and a pressurized crankcase) that pretty much
any piece of scrap iron is considered "good" by TCM.

I'm not going to champion the quality of TCM cylinders.... but
28/80???? Where did that come from? AFAIK, they still require the
calibrated orifice test (per SB03-3) to establish the minimum
allowable pressure.... and I have *never* recorded a pressure *that*
low...

It's 26/80, not 28/80, so slightly worse than you thought. G

Where does it come from? It comes straight from TCM. Used to be the
requirement for airworthiness (according to TCM) was 40/80 with audible
air leak only past the rings (anything past the valves was automatically
failing). About 10 months ago, to head off numerous lawsuits, TCM
issued an updated "standards" circular with the MUCH lower requirements
for a "good" engine.

As for the reading itself, the true reading on most of these engines is
closer to 0/80. Once the problem starts to manifest they quickly wear a
"step" near the upper part of the cylinder. Pressure is supposed to be
tested at TDC. What you will find is that the reading is essentially
0/80 (I've seen 3/80 and 7/80) when the cylinder appears to be TDC by
normal means (a dowel rod on the top of the cylinder). *BUT* you can
wiggle the prop the most microscopic amount and sometimes hit a spot
where it will suddenly jump to something more like 78/80. You've caught
the rings right under the step. [All this assumes, of course, that
there isn't too much air leaking around the valves.]

The comment from the southern USA rep for TCM - "Hell, if it will pass
the annual, why do you care?"

jmk