Sticking Lycoming O-360 valve again?

I just remembered a local chromed C-85 engine that would "sag" on
takeoff after an overhaul. It was supposedly traced to inadequate ring
gap. I find it hard to believe in your case though after your amount of
time since OH.

You might check the carb float bowl fuel level with the clear flex
standpipe connected into the carb drain port method.

Make sure the correct rocker arms are in the correct locations. On
some Lycomings they are different for the intake & exhaust. The
exhausts have oil squirt holes in them as I recall.

I'm getting outta ideas.....

wrote:
: 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.

Well, I got around to doing this today with my partner and mechanic. Pulled off the valve
covers and pulled off the rocker arms. Unfortunately, pressing on the valves did not reveal any
obvious sticking. Last time we did this (3 years and about 350 hours ago), you could push on the
valves and feel the ones that were sticking. Now, they all seem free.

After pulling off the exhaust and looking up in there, there was little more joy. Very
minimal deposits on the ports, bottom side of the valve, and stems. When having someone else depress
the valve and "wiggle" it side-to-side, it appeared to move some. It almost seems like the guide may
have trapezoidal holes... larger on the valve head side than on the rocker arm side of the guides.

The current plan is to get a tool to compress the valve springs so I can remove them. Maybe
I'll be able to get a better "feel" to them to see if maybe they're sticking in a certain rotation.
It'll also be necessary if I'm going to do SB388C.

Argh! I was *hoping* to find something obvious... so far, no joy. I don't see how even
with loose valve guides, the power could reduce like that. As far as I understand it, loose valve
guides *lead* to sticking valves.

Another possibility I thought of is if the holes are trapezoidal, being a bit tight on the
rocker-arm side, maybe taking off with CHT below 300 is the cause. I generally will get at least 200
CHT before departing, but try not to get over 300 to keep them from getting too hot on climbout.
Maybe the valves heat up faster than the cylinder heads and guides so they bind a little bit until
the CHT comes up and stabilizes. Seems like a long shot.

Oh, and the exhaust isn't in great shape, but I don't think it could be the problem. The
baffles are warped a bit inside, but still all in one piece.

-Cory

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