This is why we do runups

[Roger Long]

The particular O-320 in our 172N is the sweetest running aircraft engine I
have ever known. We maintain it rigorously and proactively and lean
aggressively for all ground operations. I have not had to clear a mag once
in the 880 hours since it was installed.

I flew the plane the day before yesterday, 15 hours out of annual with new
plugs installed. I remember being impressed again with how smooth it was.
Two of our more experienced pilots flew it after me and the last confirmed
that it was smooth when shut down.

The next morning, I started it up and taxied to the run up area. When I did
the mag check, the left was rough. The right was so rough that the airframe
was shaking visibly. There was no question about flying the plane.

When the plugs were removed, all were found fouled and one was completely
bridged. The engine ran acceptably on runup but was not as smooth as
before. It gradually returned to normal on a 4 hour flight. We're still
trying to figure out what happened. (Wild ass guesses appreciated)

The lesson here is that fouling isn't always something that gradually gets
worse. It can build up quietly and then show itself suddenly when the
electricity goes through the crud instead of the mixture. This could have
happened on a lunch time stop over, running perfectly at shutdown and then
sick after start up and a 5 minute taxi. A rough, weak engine will probably
get you down safely if it goes bad in flight but may put you in the trees on
a tight takeoff.

Don't skip that runup just because it was running fine 15 minutes ago!

--
Roger Long

[C J Campbell]

"Roger Long" m> wrote in
message .. .
| I tried all the tricks I learned with our previous, old, tired, engine and
| before we learned to lean on the ground and in descent. I did all you
| suggest until the CHT's got too high. Nada.
|

The only other things I can think of are dirty fuel, leaking valves, or
perhaps the wrong type of spark plugs was installed.

[Roger Long]

I think the most significant point is that the engine got steadily better
over an hour of subsequent cruise flight. Four hours later, it's back to
normal. If there had been an underlying cause, it should have gotten worse.

The weather here in the east has been terrible. While those in LA and
similar environs might chuckle at what we call hot and humid, we still adapt
to the conditions. Perhaps some other club members aren't as aggressive
about leaning as they should be and it hasn't been a problem until this long
muggy stretch.
--
Roger Long
>
> The only other things I can think of are dirty fuel, leaking valves, or
> perhaps the wrong type of spark plugs was installed.
>

[Ron Natalie]

"Roger Long" m> wrote in message
.. .
> I think the most significant point is that the engine got steadily better
> over an hour of subsequent cruise flight. Four hours later, it's back to
> normal. If there had been an underlying cause, it should have gotten worse.
>
Not true in general. For example, valve sticking will manifest itself when
the engine is first started which will clear up as things warm up. This doesn't
mean all is well with the engine however, eventually you may have a catastrophic
failure.

[John Galban]

"Roger Long" m> wrote in message >...
<snip>
> I flew the plane the day before yesterday, 15 hours out of annual with new
> plugs installed. <==========<<
>
> The next morning, I started it up and taxied to the run up area. When I did
> the mag check, the left was rough. The right was so rough that the airframe
> was shaking visibly. There was no question about flying the plane.
>
> When the plugs were removed, all were found fouled and one was completely
> bridged. The engine ran acceptably on runup but was not as smooth as
> before. It gradually returned to normal on a 4 hour flight. We're still
> trying to figure out what happened. (Wild ass guesses appreciated)

OK, here's my WAG. You replaced all of the plugs and they all
started fouling. Did you replace the plugs with the same brand and
heat range? Most O-320 installations have a list of acceptable heat
ranges for the plugs. I've found over the years that there is usually
one specific heat range which will prevent fouling and work perfectly
in a specific installation. It's usually found by trial and error
and when you do find it, you stick with it.

John Galban=====>N4BQ (PA28-180)

[JP Krievins]

> If only one magneto fails the check, and you have not been able to clear the
> plug after a couple of tries, it helps to run up the engine for about five
> minutes on the bad magneto.

Not that the previous poster implied this, but it is probably not a
good idea to do this five minute runup while going around the pattern,
don't ask me how I know. If it turns out to be a loose plug wire, it
doesn't fix itself, and others that the mechanic left only finger
tight may come off as well. Sometimes you can be TOO sure that you
have a fouled plug.

This IS why we do runups....but ya gotta listen to what the airplane
is trying to tell you.

JP Krievins

[Rick Durden]

Roger,

You have people who are running the engine full rich all the time. It
was not built for 100LL fuel, so it needs to be leaned in cruise and
in descent and in climb above 5,000 density altitude. It doesn't hurt
to lean it when taxiing as well, but do so very aggressively, so that
if you forget to go to full rich before takeoff it will quit on you
rather than make a takeoff with the mixture other than at full rich.

Once you lean the airplane for cruise you need not change the mixture
on the descent. The checklist says to enrichen as necessary to avoid
roughness, so don't enrichen the mixture unless the engine runs rough.
When you run the prelanding checklist on downwind and pull the carb
heat, that's a pretty good time to go to full rich (if you want to) in
anticipation of a go around. Otherwise, leave it where it is until
you pull it the rest of the way out to shut the engine down as you
park. If you make a go around, push the mixture to rich, carb heat to
cold and apply full throttle. Some folks don't like the extra work
with the mixture at that time, so they go to full rich on downwind,
base or final to be ready for a go around. They lean again after
turning off of the runway to avoid plug fouling.

All the best,
Rick

"Roger Long" m> wrote in message >...
> The particular O-320 in our 172N is the sweetest running aircraft engine I
> have ever known. We maintain it rigorously and proactively and lean
> aggressively for all ground operations. I have not had to clear a mag once
> in the 880 hours since it was installed.
>
> I flew the plane the day before yesterday, 15 hours out of annual with new
> plugs installed. I remember being impressed again with how smooth it was.
> Two of our more experienced pilots flew it after me and the last confirmed
> that it was smooth when shut down.
>
> The next morning, I started it up and taxied to the run up area. When I did
> the mag check, the left was rough. The right was so rough that the airframe
> was shaking visibly. There was no question about flying the plane.
>
> When the plugs were removed, all were found fouled and one was completely
> bridged. The engine ran acceptably on runup but was not as smooth as
> before. It gradually returned to normal on a 4 hour flight. We're still
> trying to figure out what happened. (Wild ass guesses appreciated)
>
> The lesson here is that fouling isn't always something that gradually gets
> worse. It can build up quietly and then show itself suddenly when the
> electricity goes through the crud instead of the mixture. This could have
> happened on a lunch time stop over, running perfectly at shutdown and then
> sick after start up and a 5 minute taxi. A rough, weak engine will probably
> get you down safely if it goes bad in flight but may put you in the trees on
> a tight takeoff.
>
> Don't skip that runup just because it was running fine 15 minutes ago!

[Roger Long]

Rick,

That's pretty much the way I fly the plane although I land at a partially
leaned setting I know from experience will give me full power without
stumbling if I have to go around and forget the mixture.

I've posted stuff on our club web site about leaning and preach it every
chance I get. Everyone I've talked to assures me that they are leaning.
Than, I talked to someone today who said, "I lean all the time but I never
pull it out more than an inch because I'm afraid of overheating it." Ah,
the picture is becoming a little clearer. That engine hardly feels it at an
inch.

This engine has an unusually good mixture distribution for an O-320. There
is very little roughness or stumbling before it quits and it's easy to stall
leaning to the max on the ground. I think this makes people gun shy about
seeing too much shiny metal ahead of the red knob.

I guess I've got to push the issue more. It's hard though to change long
time habits learned from revered CFI's who had 10 times the hours I have.
We had three hours shop time instead of three hours flight time yesterday.
Price of habit I guess.

--
Roger Long

[Wayne]

I noticed that the runup is pretty bad on my new plane. I started
leaning during taxi and it helped a little, but not as much as i thought it
would. Then I tried leaning for the taxi back, and flew again the next
morning and leaned again on taxi, big improvement. The one other partner
told me always to use two pumps of primer, even if it was just running five
minutes ago. I think they are drowning the bottom plugs, and then running
rich on taxi. The plane requires about two inches of leaning on the mixture
control to get it clean. I have yet to check the RPM rise before lean cutoff
to see if the idle mixture itself is too rich. We adjusted the mixture on
the IO-360 (on the bi-plane) and wow, what a difference in all around
performance! This one is an O-360 though.

Oh yeah, the roughness is about the same on either mag but goes totally
away when on both.
Suggestions?

Wayne


"Roger Long" m> wrote in
message .. .
> I think the most significant point is that the engine got steadily better
> over an hour of subsequent cruise flight. Four hours later, it's back to
> normal. If there had been an underlying cause, it should have gotten
worse.
>
> The weather here in the east has been terrible. While those in LA and
> similar environs might chuckle at what we call hot and humid, we still
adapt
> to the conditions. Perhaps some other club members aren't as aggressive
> about leaning as they should be and it hasn't been a problem until this
long
> muggy stretch.
> --
> Roger Long
> >
> > The only other things I can think of are dirty fuel, leaking valves, or
> > perhaps the wrong type of spark plugs was installed.
> >
>
>
>

[[email protected]]

One thing to remember is that for most operations, even at sea level, full
rich is too rich. Consider this: The full rich mixture setting must not be
too lean for any condition likely to be encountered, as the pilot obviously
has no way to further enrich the mixture. But at -30 C at sea level (a temp
sometimes seen in winter in many parts of the country) and barometric
pressure of 29.92", density altitude is MINUS 5900 feet! If full rich
mixture is not too lean for those conditions it sure as heck will be too
rich at sea level in standard conditions. I'm not advocating leaning for
takeoff at or close to sea level, as a rich mixture may be required for
adequate cooling, but I always start to lean fairly early in the climb.

-Elliott Drucker

[Dennis O'Connor]

Elliot, you can expect the leaning police to come and take you away...
Heresy, that's what it is, heresy....
Denny
> wrote in message
...
> One thing to remember is that for most operations, even at sea level, full
> rich is too rich.

[Dennis O'Connor]

Rick, good advice... Everyone operates a bit differently... For a routine
approach and landing I leave the mixture and prop set at cruise the whole
way until shutdown on the ramp... If I need to go around it is a burned in
habit that everything goes to the firewall with one, fingers spread wide,
push....
That will change if I am landing at a fly-in with oodles of traffic or if
the weather is rough and scummy, then I will bring the props up to 2500 and
mixture 90% rich about the time I turn final, since the odds that I will
need to jockey the power are greater in those conditions...

Denny
"Rick Durden" > wrote in message
m...
> Roger,
>
> You have people who are running the engine full rich all the time. It
> was not built for 100LL fuel, so it needs to be leaned in cruise and
> in descent

[John Galban]

(Rick Durden) wrote in message >...
<snip>
> When you run the prelanding checklist on downwind and pull the carb
> heat, that's a pretty good time to go to full rich (if you want to) in
> anticipation of a go around. Otherwise, leave it where it is until
> you pull it the rest of the way out to shut the engine down as you
> park. If you make a go around, push the mixture to rich, carb heat to
> cold and apply full throttle. Some folks don't like the extra work
> with the mixture at that time, so they go to full rich on downwind,
> base or final to be ready for a go around. They lean again after
> turning off of the runway to avoid plug fouling.


Argh! This business about going to full rich in anticipation of a
go-around might be OK for flatland pilots, but it is not a good
practice generally. If you are at a high density altitude (could be a
med. altitude airport in the summer), going full rich for landing
might leave you in the trees if you attempt a go around. I've seen
this happen more times than I care to remember.

Rather that repeating the inaccurate landing checklist item,
"mixture - full rich", how about a new one. "Mixture - set
appropriately".

John Galban=====>N4BQ (PA28-180)

[Roger Long]

We try to stay on top of everything on this engine and not begrudge it a
penny. The mags are done every 500 hours and are only a couple hundred out.
We have the basics checked every 100 - 150 hours, pull the lifters, etc.
This has certainly paid off in an engine that has always run like a top with
not even minor plug fouling till now. It starts almost as well in the dead
of winter with a oil pan preheat as it does in the summer. Meanwhile, the
flight school planes are going "grind, grind, grind, grind, grind, grind,
grind, grind, grind..."

--
Roger Long
JerryK > wrote in message
...
> How long since the mags were overhauled? It is supposed to be done every
> 500 hours or so.

[Jim Vadek]

"Rick Durden" > wrote in message
m...

> Once you lean the airplane for cruise you need not change the mixture
> on the descent. The checklist says to enrichen as necessary to avoid
> roughness, so don't enrichen the mixture unless the engine runs rough.

Yes, but that statement should be further qualified by saying that descents
should be made at less than 75% power or else EGT and CHT could exceed
operating limits. 65% power sounds like a good number. Some carbed engines
with good fuel distribution will run smooth when too lean (close to peak,
either rich or lean of peak).

[Dylan Smith]

On 20 Aug 2003 12:24:20 -0700, Rick Durden > wrote:
>park. If you make a go around, push the mixture to rich, carb heat to
>cold and apply full throttle. Some folks don't like the extra work
>with the mixture at that time, so they go to full rich on downwind,

Depends on the aircraft. On many aircraft, you can push prop, mixture
and throttle forward at the same time with one hand which makes it easier
to follow that practise.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

[Bob Fry]

(Rick Durden) writes:

> It doesn't hurt
> to lean it when taxiing as well, but do so very aggressively, so that
> if you forget to go to full rich before takeoff it will quit on you
> rather than make a takeoff with the mixture other than at full rich.

Rick, I had a talk with my mechanic a couple of months ago about
leaning when idling. He says for my carburator and C-90 engine, and I
suppose many other aircraft engines, leaning at idle doesn't do
anything unless it is nearly at idle cutoff. It is only when the RPMs
are well above idle that the mixture control begins to really control.
So does leaning on the ground--during idle--do anything unless it is
leaned nearly to idle cutoff?

[Ray Andraka]

The idea is in fact to lean aggressively on the ground. I lean mine till
it stumbles then turn the vernier in just till it is smooth. That works
out to pretty close to idle cutoff. Leaning this aggressively, the engine
will quit if you advance the throttle, making it impossible to take off
with it still leaned.

Bob Fry wrote:

> (Rick Durden) writes:
>
> > It doesn't hurt
> > to lean it when taxiing as well, but do so very aggressively, so that
> > if you forget to go to full rich before takeoff it will quit on you
> > rather than make a takeoff with the mixture other than at full rich.
>
> Rick, I had a talk with my mechanic a couple of months ago about
> leaning when idling. He says for my carburator and C-90 engine, and I
> suppose many other aircraft engines, leaning at idle doesn't do
> anything unless it is nearly at idle cutoff. It is only when the RPMs
> are well above idle that the mixture control begins to really control.
> So does leaning on the ground--during idle--do anything unless it is
> leaned nearly to idle cutoff?

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

[Roger Halstead]

On Thu, 21 Aug 2003 21:42:44 GMT, "Roger Long"
m> wrote:

>We try to stay on top of everything on this engine and not begrudge it a
>penny. The mags are done every 500 hours and are only a couple hundred out.
>We have the basics checked every 100 - 150 hours, pull the lifters, etc.
>This has certainly paid off in an engine that has always run like a top with
>not even minor plug fouling till now. It starts almost as well in the dead
>of winter with a oil pan preheat as it does in the summer. Meanwhile, the
>flight school planes are going "grind, grind, grind, grind, grind, grind,
>grind, grind, grind..."

I use a progressive maintenance program, but....
I have the mags checked at annual. Only checked. Both have close to
1300 hours on them. I did replace the plugs at roughly 600 hours.
I've never had a problem with plug fowling on the Deb. Compression is
still good.. The vacuum pump is original on the engine at close to
1300 hours so it doesn't have much farther to a Factory reman.

As it has no filter I change oil at 25 hours. At 25 hours it's
difficult to see if the level is down at all. Probably a pint or
less.

It runs smooth and starts easy. I have a Tanis heater on each
cylinder head and on the case. Once the temperatures fall below
freezing the heater stays on 24 X 7 with the entire front of the plane
wrapped in two layers of space age blankets which actually extend well
beyond the firewall.

I get very close to 190 cruise on 13 1/2 to 14 GPH. I always cruise
at 75% unless too high to be able to get 75%.

I've never found it necessary to lean while on the ground except when
I was at Goodland KS and Jefco. There I leaned for takeoff. I either
run 24 X 24, or adjust to one inch over square adjusted for 75%. The
one thing I want to add to the engine are gami injectors and monitor
the EGT and CHTs on all 6.

I have had one complete engine failure and that was due to the
diaphragm in the fuel cutoff valve located in the distribution block
(spider) on top of the engine.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

[David Megginson]

Chris Kennedy > writes:

>> Rick, I had a talk with my mechanic a couple of months ago about
>> leaning when idling. He says for my carburator and C-90 engine,
>> and I suppose many other aircraft engines, leaning at idle doesn't
>> do anything unless it is nearly at idle cutoff. It is only when
>> the RPMs are well above idle that the mixture control begins to
>> really control. So does leaning on the ground--during idle--do
>> anything unless it is leaned nearly to idle cutoff?
>
> Up here in the mountains we lean to the point of stumbling and try not
> to reduce RPMs below 1200 on our O-540 (as does the local FBO with its
> O-360). Except on very cold winter days we lean for departure as
> well.

As far as I understand, carbureted engines have a separate idle
mixture control that needs to be adjusted with a screwdriver on the
carburetor itself (i.e. on the ground, by an A&P). If that is set too
rich, you can lean during ground idle until the cows come home and
still end up with fouled plugs.


All the best,


David

--
David Megginson, , http://www.megginson.com/

[Rick Durden]

Jim,

> Yes, but that statement should be further qualified by saying that descents
> should be made at less than 75% power or else EGT and CHT could exceed
> operating limits. 65% power sounds like a good number. Some carbed engines
> with good fuel distribution will run smooth when too lean (close to peak,
> either rich or lean of peak).

Actually, that doesn't make sense. I think you may mean
"inappropriately" lean, rather than too lean. The worst spot is about
50 degrees rich of peak when at high power as that is generally max
for CHT and BMEP. So long as you are richer or leaner than that, you
aren't going to hurt the engine. Leaner is generally better in terms
of keeping temps down and plugs from fouling, so long as the engine
runs smoothly.

All the best,
Rick

[Jim Vadek]

"Rick Durden" > wrote in message
...
> Jim,
>
> > Yes, but that statement should be further qualified by saying that
descents
> > should be made at less than 75% power or else EGT and CHT could exceed
> > operating limits. 65% power sounds like a good number. Some carbed
engines
> > with good fuel distribution will run smooth when too lean (close to
peak,
> > either rich or lean of peak).
>
> Actually, that doesn't make sense. I think you may mean
> "inappropriately" lean, rather than too lean. The worst spot is about
> 50 degrees rich of peak when at high power as that is generally max
> for CHT and BMEP. So long as you are richer or leaner than that, you
> aren't going to hurt the engine. Leaner is generally better in terms
> of keeping temps down and plugs from fouling, so long as the engine
> runs smoothly.

Yup. I did not explain it very well.

[John Galban]

David Megginson > wrote in message >...
> Chris Kennedy > writes:
>
> >
> > Up here in the mountains we lean to the point of stumbling and try not
> > to reduce RPMs below 1200 on our O-540 (as does the local FBO with its
> > O-360). Except on very cold winter days we lean for departure as
> > well.
>
> As far as I understand, carbureted engines have a separate idle
> mixture control that needs to be adjusted with a screwdriver on the
> carburetor itself (i.e. on the ground, by an A&P). If that is set too
> rich, you can lean during ground idle until the cows come home and
> still end up with fouled plugs.

From Chris's description, he's leaning to just above idle cutoff.
That will do the trick no matter how your idle mixture is set. On my
O-360, the mixture control is just above idle cutoff and the most rpms
I can make are about 1200. Leaning that aggresively guarantees that
you will not take off without enrichening the mixture.

John Galban=====>N4BQ (PA28-180)

[Pat Barry]

Dear John:

Mechanically and technically, and while I'm not doubting your post and your experience with plugs,
this makes no sense.

If plugs are cleaned and gapped there is just no cause attributable to plugs that would lead to extra
fouling. If, however, the plugs had worn to the level where the electrodes are spaced too far apart I
can see where the uneven spark would cause uneven combustion which, in turn, would cause lead
fouling.

I'm racking my brain to think where time in service would make a difference - and the only conclusion
is mechanical failure, possibly a cracked ceramic area of some type of wear, if other than the
electrode gap?

If you ever learn more for the reason I'd sure like to learn about it.

My experience has been that plugs will last until the electrode tips are worn and unreliable - and
this can be 1000 hours or more if the cylinders are in good shape. If I had to make a guess, I'd say
that while plugs may be well maintained, they can wear due to heat or lean of peak operation etc.,
and that this may shorten plug life.

Pat




John Galban wrote:

> "Dan Luke" <c172rgATbellsouthDOTnet> wrote in message >...
> >
> > Is your O-360 bad about fouling plugs? Mine's terrible - much worse than the
> > O-320s on the Skyhawks I used to fly. I have to be an absolute fiend about
> > leaning to keep my plugs clear.
>
> It's not nearly as bad as my O-300 was when running 100LL. Overall,
> it's not really a huge problem. If I forget to lean for a long taxi,
> I stand about a 50/50 chance that I'll foul a plug. It's usually
> minor fouling and clears up after about 10 seconds of leaning durning
> the run up.
>
> Over the years, I've noticed that the age of the plugs has an effect
> on fouling. When the plugs start getting around 400 hrs on them,
> they tend to foul easier.
>
> John Galban=====>N4BQ (PA280-180)

[Paul Mennen]

> while plugs may be well maintained, they can wear due to heat
> or lean of peak operation etc., and that this may shorten plug life.
>
> Pat

Assuming your engine runs smooth when LOP, LOP operation should
increase plug life, not shorten it. Plug fowling will be much
less likely, and assuming you are operating far enough into the
LOP range, the cylinders and plugs will be running cooler.

~Paul

[John Galban]

Pat Barry > wrote in message >...
> Dear John:
>
> Mechanically and technically, and while I'm not doubting your post and your experience with plugs,
> this makes no sense.
>
> If plugs are cleaned and gapped there is just no cause attributable to plugs that would lead to extra
> fouling. If, however, the plugs had worn to the level where the electrodes are spaced too far apart I
> can see where the uneven spark would cause uneven combustion which, in turn, would cause lead
> fouling.
>
> I'm racking my brain to think where time in service would make a difference - and the only conclusion
> is mechanical failure, possibly a cracked ceramic area of some type of wear, if other than the
> electrode gap?

While I don't have any specific data, I've always assumed that it's
some type of wear. I generally get about 700 hrs. out of a set of
plugs. That's about the point where the electrodes start taking on a
football shape. When replaced with brand new plugs, I always noticed
that the propensity for fouling decreased. Upon reading your post, I
see you're point. As the plugs aged, one or more may have had some
sort of mechanical problem that caused a weaker spark (as evidenced by
the increased fouling).

John Galban=====>N4BQ (PA28-180)