Flight test report and intake leak question

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

"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. Then spray soap solution on the intake pipes and
watch for bubbles. Same trick works for finding exhaust leaks.

Works on cars too. I pressurized the intake of a Jeep V8 and found a couple
of pretty good vacuum leaks.

Bill Daniels

In . net 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.

Fouled plug? Bad lead to plug?

----------------------------------------------------
Del Rawlins-
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I use the blow side of a VERY CLEAN shop vac to pressurize the intake. Use
cardboard and a lot


good idea.......buttttt....

One thing to worry about here....

Some (most) shop vacs rely on the air flowing through the motor to keep the
motor cool...

If you run a shop vac to provide a low air pressure source and youve got it all
plugged up so that very little air is actually FLOWING...I imagine you could
destroy it pretty quickly...

If you are gonna do this, you need to alternate short periods of time where the
vac is providing pressure but no real air flow with significantly longer
periods of time where you allow the air to flow freely to cool the engine back
down....

Note that just running a short period of time with it plugged, then shutting it
off wont really help in the cooling department....unless you wait on the order
of hours before you crank it up again

Maybe Im being paranoid and/or shop vacs today are built like brick
****houses.....but I m cheap enough to not risk a couple cases of beer money to
find out the hard way....

Oh yeah...NEVER ever use a shop vac to clean out a charcoal grill or fireplace
even if its been days since the fire...and as if you need to be told
this....never use a shop vac to clean up a gasoline spill (yes I know someone
who did this)

good luck!

Blll

Del Rawlins wrote:

Fouled plug? Bad lead to plug?

I forgot to mention: New mags, plugs, and harness.
Swapped plugs across the engine, same problem.
Harness checks good.

Dave 'stumped' Hyde

I have seen auto mechanics use an unlit propane torch at a very low setting.
Directing it around the gaskets of a running engine, causes a very
noticealbe RPM increase, should a leaking intake system be present. One has
to be aware to keep the propane away from the normal fuel air intake. I
don't know if this system of testing would be proper in an aviation
instance, where the prop wash may interfere. Maybe, feeding the propane
very close to the area to be checked, in small plastic tubing may help.

In et nauga wrote:
Del Rawlins wrote:

Fouled plug? Bad lead to plug?

I forgot to mention: New mags, plugs, and harness.
Swapped plugs across the engine, same problem.
Harness checks good.

Did you try swapping the mags? A long shot for sure, but you never know.

----------------------------------------------------
Del Rawlins-
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Unofficial Bearhawk FAQ website:
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"Charles S" wrote in message
nk.net...
I have seen auto mechanics use an unlit propane torch at a very low
setting.
Directing it around the gaskets of a running engine, causes a very
noticealbe RPM increase, should a leaking intake system be present. One
has
to be aware to keep the propane away from the normal fuel air intake. I
don't know if this system of testing would be proper in an aviation
instance, where the prop wash may interfere. Maybe, feeding the propane
very close to the area to be checked, in small plastic tubing may help.



That big fan on the front of the aircraft engine keeps blowing the propane
away. Anyway this works best with a lean burn engines where the additional
fuel seeping in through the intake leak moves the mixture toward best power.

Bill Daniels

Del Rawlins wrote:

In et nauga wrote:
Del Rawlins wrote:

Fouled plug? Bad lead to plug?

I forgot to mention: New mags, plugs, and harness.
Swapped plugs across the engine, same problem.
Harness checks good.

Did you try swapping the mags? A long shot for sure, but you never know.

----------------------------------------------------
Del Rawlins-
Remove _kills_spammers_ to reply via email.
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/

Before swapping the mags, I'd pull the cigarette plugs out and
take a close look at the contacts.

We had a weak mag on the Taylorcraft last summer that we chased
for months. Finally checked these guys and fount the problem.

Our cigarette plugs were probably origional equipment on this
engine (A-65 built in -=1939=-).

Sure, it's a long shot, but an easy one to eliminate.

best of luck.

Richard

Problem solved!

It rained on and off all day today, so I had plenty
of down-time. The cowl came off and I retorqued the
intake bracket; loosened the intake hose, slid it
up the pipe a fraction of an inch and retorqued it;
and pulled the manifold pressure tap(*) from the
primer port and plugged the port. Started it
up and waddaya know, it idled really well on
either and both mags. Put the MAP line back
in the primer port and tried it again. Still
smooth, but *maybe* a little rougher than before.
Capped and stowed the MAP line and replugged the
cylinder. I'll put a restrictor fitting in later
just in case. I don't know which thing fixed it,
but it's fixed. It was much easier to set the
idle mixture when one cylinder wasn't sucking air.
Now I'm wondering which cylinder will be the hottest
now that #3 isn't leaner than the rest. Just have
to fly it and see :-)

Thanks to everyone for the suggestions, on and offline.

Dave 'Hoover' Hyde


(*) Forgot to mention this was on the problem
cylinder too. #1,2, and 4 are primed.