Sticking Lycoming O-360 valve again?

Have you done the "wobble check" on the valves?

wrote:
Hey all. Question about my Cherokee's O-360. When we first got it about 3.5
years ago, it was very low hours SOH, but almost 10 years. We had some sticking
valves and bad oil consumption, so sent the jugs out to have the IRAN. At that time,
in addition to the the IRAN, a few rusted valve springs were replaced with servicable
ones by Triad Aviation. Broke in and settled on about 1qt/8 hours on chrome jugs...
good by all I've talked to. Ran fine, although the max static runup I'd ever seen was
right in the midrange.... 2350 or so. Often it was on the low end... 2275-2300.

For a little while now (6 months or so), it seems to have a bit of
"mid-morning" sickness. It starts up and runs smooth and fine. Taxis smooth, runup
good, mags fine. On the takeoff/climbout, it just doesn't "feel right." Not bad
enough to know something's amiss, just enough to look at the VSI and say, "Hrm... I
should be getting a little better climb than this." Usually within a minute or two of
liftoff, it picks back up and I get an additionall 200 fpm or so. The usual
in-flight diagnostics reveal nothing.... mixture, carb heat, mags, fuel pressure,
CHT/EGT, etc. Runs smooth on either mag (with reduced power)... on high DA days
leaning it a bit might be necessary, etc.

Sounds a lot like a sticking valve, but I think I've done everything that can
be done to prevent that. Baffling is in great shape. I never allow climb CHT over
400 or cruise over 380... and that's on the *spark-plug* CHT probes... They've been
verified reading at 50-60 degrees hotter than the bayonet-style that Lycoming uses, so
the CHT is actually 325-350 max. I generally cruise no higher than 65% and lean to
about peak EGT as per Piper/Lycoming recommendations, so there shouldn't be much for
rich combustion byproduct buildup.

Other suggestions? I'm figuring to pull off the rocker-box covers, push on
the valves, and see if I can feel friction in any of them.

Thanks,
-Cory

Otis Winslow wrote:
: Have you done the "wobble check" on the valves?

Not since the shop did the IRAN 3 years ago. It was the relatively close-by
Triad (Lycoming certified repair center), so I'd assume that was part of the
inspection.

-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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