Flight test report and intake leak question

You may have loose bearings in the mag that runs rough at idle.
A mag test at idle will almost always run rough if the bearings or the
rotor shaft are worn since the rotor has time to flop around at low
speed which changes the timing a lot. At the normal mag test rpm the
mag rotor tends to float in the center and work normally.

The mag idle test will also show up as rough if the plug gaps are too
large or the internal mag distributor is set one tooth off or to the
wrong rotation since the mag output is less at idle.

I would check the #3 plug on a pressurized plug tester or just
replaced the plug. I once had a new plug that was broken inside that
drove me nuts trying to find a random intermittent miss on a
helicopter.

On Sat, 10 Apr 2004 02:47:59 GMT, "nauga" wrote:

My Lyc. O320-D2C idles rough on the right mag, with the
#3 cyl showing an EGT drop. The roughness clears up
above 1200 RPM or so, still on one mag. It's also
noticably smoother on just the left mag, and everything's
smooth on both mags. In flight #3 CHT runs 50 degF hotter than
the rest, as well as higher EGT, which is not unusual in RVs
(I'm told)...dunno if this is also related in my case. General
consensus around here is it's either because the engine isn't
broken in yet (10 hours STOH, all at high power so far) or an
intake leak on #3. Has anyone got any suggestions on how to
find an intake leak that don't involve standing close to a
turning propellor? Any other troubleshooting advice?
Timing checks good for both mags, BTW. Chrome cylinders,
bayonet CHT probes.

In other news, with the engine throttled back a bit for temps
and the airpseed up for cooling, flight tests are going well.
Adapted from an e-mail one of you might recognize:
165 KIAS tops so far, and that's without wheel pants and
throttled back a little to keep the CHT under control.
Stall points are done. I think I've got the only -4 with
stall warning. With the flaps down the stick shakes like
mad (+/- 1", 3-4 Hz) prior to stall and airplane shudders
hard about 1/2 knot before. The shudder isn't usable as
warning, but the stick sure is.
4g turns are awesome. My g-tolerance has faded
completely, so I'm pulling up to 4 as often as I can
to get some tolerance back before going out to 6. I've
already got the gloc box checked (not in this airplane!).
Haven't had the nerve (or a plan) to roll it yet, but
I've been to about 135 deg doing pitchbacks to keep the
speed and g up. Snuffed the engine when I pushed over to
stop it ballooning after rolling out from an overbank
yesterday. It started right up again, it was just a
little unexpected at the time. I found the seat cushion
sometime after landing. Today was more of the same...without
the unload.
Landings are much easier, but I still tend to drop it in.
The RV-4 seems really good-natured on the ground, thank goodness.

Supposed to rain tomorrow. Maintenance day!

Dave 'testy' Hyde

"Bill Daniels" wrote in message news:mSJdc.103965$gA5.1394034@attbi_s03...
"nauga" wrote in message
ink.net...
Has anyone got any suggestions on how to
find an intake leak that don't involve standing close to a
turning propellor? Any other troubleshooting advice?
Timing checks good for both mags, BTW. Chrome cylinders,
bayonet CHT probes.

Dave 'testy' Hyde



I use the blow side of a VERY CLEAN shop vac to pressurize the intake. Use
cardboard and a lot of duct tape to seal off the air box and fit the vacuum
hose. You have to plug the exhaust too since a cylinder may have both intake
and exhaust valves open.

We use the shop vac thing to pressurize the exhaust system to
check for monoxide leaks in the cabin heat system, as per the Canadian
AD that applies to all Canadian aircraft, and also required by Cessna
on their airplanes in the latest maintenance schedules. The intake and
exhaust valves have so little overlap that they present no problem,
and if there is any, a slight turn of the prop stops it. And we find
leaks in those exhaust systems, too, before they get dangerous. Leaks
you'd never spot with your eyeballs alone.
Another respondent was concerned about vacuum motor life, and he's
right. Got to avoid running the vac for too long with so little
airflow through it. We use an old household canister vacuum, reserved
just for this sort of thing, thoroughly cleaned out, no bag or
anything, and labelled clearly.

Dan