Priming the engine and Mag check questions

A person told me it is better to push the primer slowly rather
then quick shots.

Slower is better on pulling out the primer as this allows the primer cylinder
to draw in all the fuel it can take. Pushing the charge in quickly is probably
best as the velocity may help in atomizing the fuel

..Another person said I should hesitate before going
back to both mags when checking the mags. He says that I should let it
run on one mag for 3 or 4 seconds. All I am checking for is the drop.

When doing the mag check whichever mag you are on you want to let the RPM fall
until it stabilizes. At that point you note the drop. Depending on the engine
and magneto this could be anywhere from 50 to 150 RPM. Typically it is 50 RPM
and anything over 100 is worth looking into even if you think the engine is
running fine and making RPM at power. The point is to let the engine RPM
stabilize while running on each mag individually. If you quickly flip from
left to right and back to both as soon as you see the RPM decay you might miss
something crucial like an entire magneto not even working or a drop of 200 or
more in RPM or even fouled spark plugs.

John Dupre'

I have an old tired engine in my plane that requires 7 strokes of prime
no matter what, cold hot or warm. No biggie, as it starts everytime
within 3 turns of the prop. I don't have to crank for any period of
time. A person told me it is better to push the primer slowly rather
then quick shots. Mechanically inclined I am not, but does it make a
difference? I have not noticed any difference trying it either way.

Mag check. On runup, I check both mags by flipping the switch to mag
one and mag two. Another person said I should hesitate before going
back to both mags when checking the mags. He says that I should let it
run on one mag for 3 or 4 seconds. All I am checking for is the drop.
Is there a benefit to letting the engine run on one set of mags for a
period of time during the runup?

Thanks for any input.

Allen

just noting the "Drop" you'll know the "ground" is working.. not that the
remaining mag can support the engine..

BT

"JDupre5762" wrote in message
...
A person told me it is better to push the primer slowly rather
then quick shots.

Slower is better on pulling out the primer as this allows the primer
cylinder
to draw in all the fuel it can take. Pushing the charge in quickly is
probably
best as the velocity may help in atomizing the fuel

.Another person said I should hesitate before going
back to both mags when checking the mags. He says that I should let it
run on one mag for 3 or 4 seconds. All I am checking for is the drop.

When doing the mag check whichever mag you are on you want to let the RPM
fall
until it stabilizes. At that point you note the drop. Depending on the
engine
and magneto this could be anywhere from 50 to 150 RPM. Typically it is 50
RPM
and anything over 100 is worth looking into even if you think the engine
is
running fine and making RPM at power. The point is to let the engine RPM
stabilize while running on each mag individually. If you quickly flip
from
left to right and back to both as soon as you see the RPM decay you might
miss
something crucial like an entire magneto not even working or a drop of 200
or
more in RPM or even fouled spark plugs.

John Dupre'

A Lieberman wrote:

A person told me it is better to push the primer slowly rather
then quick shots.

The primers on the two aircraft I have owned both were slow to fill. If you
pulled the primer out rapidly, you wouldn't get much (if any) gas into the
primer. Once the primer is full, however, I don't think it makes any
difference whether you push it rapidly or slowly.

Is there a benefit to letting the engine run on one set of mags for a
period of time during the runup?

You should let it run on one for a few seconds (I count 4 when I do a runup).
This lets you make sure that the drop is not excessive. I switch back to
both for a few seconds before changing to the second mag.

George Patterson
The optimist feels that we live in the best of all possible worlds. The
pessimist is afraid that he's correct.
James Branch Cavel

The priming question has been answered

However on the mag drop----

If there is a bad or fouled plug, you will see a drop as soon as the
good mag is switched off.

If however there is a timing error which can be caused by the points
wearing, or the magneto itself slipping position due to loose hold down
nuts---then the drop will be much slower taking several seconds to
stabilize.

If you switch too quickly during the mag check you might miss this.

Cheers:

Paul

clyde woempner wrote:

I would think, the question should be, where do I get an old tired engine
rebuilt??
Clyde

Clyde,

I might be making it sound worse then what it may be. The engine has
2017 hours. (Lycoming 360 180 hp) The compressions are 76/76/76/78 out
of 80. I bought the plane in January of this year and at that time the
engine had 1940 hours. So, you can see, it has been flown much more in
the past 6 months then it has in quite some time. The engine does purr
like a kitten, and is easy to start (after figuring out I need to prime
it so much).

My A&P is saying for now, with the compressions so high, and no metal in
the oil, not to fix what is working. He said he has replaced engines
with lower compressions then what I have in. Figuring he is the
expert, who am I to question.

Allen

G.R. Patterson III wrote:

The primers on the two aircraft I have owned both were slow to fill.

I think this is the same experience I am having. In the training
airplanes, I "primed" by pushing the throttle in and out. I never had to
use the primer knob.

In my own plane, when I pull the primer out, I don't feel resistance
until the 4th or 5th pull of the primer. After that I feel some
resistance.

You should let it run on one for a few seconds (I count 4 when I do a runup).
This lets you make sure that the drop is not excessive. I switch back to
both for a few seconds before changing to the second mag.

I did this for the last 3 flights I took, and didn't notice a drop after
the 50 rpm drop. Generally, when I do this, and there is carbon on the
sparks, I get a dramatic drop. I then go back to both mags, lean it out
til the engine runs rough, let it run for 5 to 10 seconds, and that
clears up my mag check. The mixture is not like a Cessna where I can
"fine tune" it by turning the knob. It is a lever like the throttle
where I push it in or pull it out. I will continue to run the mag check
as you suggested for 4 seconds.

I posted this question as I wanted to be sure I wasn't doing more damage
then good by letting it run longer then needed on one mag.

Allen

I would think, the question should be, where do I get an old tired engine
rebuilt??
Clyde

"A Lieberman" wrote in message
...
I have an old tired engine in my plane that requires 7 strokes of prime
no matter what, cold hot or warm. No biggie, as it starts everytime
within 3 turns of the prop. I don't have to crank for any period of
time. A person told me it is better to push the primer slowly rather
then quick shots. Mechanically inclined I am not, but does it make a
difference? I have not noticed any difference trying it either way.

Mag check. On runup, I check both mags by flipping the switch to mag
one and mag two. Another person said I should hesitate before going
back to both mags when checking the mags. He says that I should let it
run on one mag for 3 or 4 seconds. All I am checking for is the drop.
Is there a benefit to letting the engine run on one set of mags for a
period of time during the runup?

Thanks for any input.

Allen

"Paul Millner" wrote in message ...
Well, that's really not evident from the data you shared... maybe it was
flying 500 hours/year before you bought it? But compressions only tell you
about the top of the engine. Is there any valve train wear, are you still
getting full horsepower, or have the tappets worn so you're not getting full
valve lift? Do you really want to run the engine until the $5,000
crankshaft starts machining its way through the main bearing backing plates,
turning it into junk?

These are imponderables, perhaps, but saying, "the compressions are good so
I'm going to keep on flying" ignores some major factors in economic
ownership.

Figuring he is the expert, who am I to question.

Well, you're paying the bills not him, and it's your butt in the air, not
his... and who's pilot in command, anyway? :-)

Paul

The Type Certificate Data Sheets will give minimum and maximum
static full-throttle RPMs for that engine/prop combination in that
airplane, and if there is valve train wear the RPM will be out of the
range. This isn't rocket science. If the crank is eating its way into
something, there'll be metal in the filter. That's simple enough, too.
If the oil pressure is well into the green, and doesn't drop to zero
at idle when hot, the bearings are OK. If the compressions are as high
as he's indicated, there isn't much wrong with the top end of the
engine, other than perhaps corroded valve stems.
Lycomings have been known to swallow valves when the head broke
off the stem because of corrosion pitting in engines that have been
run for short periods and left to sit. Similarly, the crankshafts in
these engines build up water/oil sludge in the crank nose (unless it's
driving a constant-speed prop) and this causes dangerous corrosion
that can result in propeller departure.
Lycomings run regularly on long flights have reached 4000 hours
without overhauls.
Tell me what airplane it's in and I'll look up the prop RPM range
for you.

Dan

Allen,
I'd recommend contacting a lab that does Oil sample analysis for
aircraft engines, and having them run a couple of samples. They should
tell you what to do prior to taking your sample for analysis. Like "do a
oil change, run the engine for x hours, drain, run x hours, and take
sample.
Bill Higdon

A Lieberman wrote:
Dan Thomas wrote:


The Type Certificate Data Sheets will give minimum and maximum
static full-throttle RPMs for that engine/prop combination in that
airplane, and if there is valve train wear the RPM will be out of the
range. This isn't rocket science. If the crank is eating its way into
something, there'll be metal in the filter. That's simple enough, too.
If the oil pressure is well into the green, and doesn't drop to zero
at idle when hot, the bearings are OK. If the compressions are as high
as he's indicated, there isn't much wrong with the top end of the
engine, other than perhaps corroded valve stems.
Lycomings have been known to swallow valves when the head broke
off the stem because of corrosion pitting in engines that have been
run for short periods and left to sit. Similarly, the crankshafts in
these engines build up water/oil sludge in the crank nose (unless it's
driving a constant-speed prop) and this causes dangerous corrosion
that can result in propeller departure.
Lycomings run regularly on long flights have reached 4000 hours
without overhauls.
Tell me what airplane it's in and I'll look up the prop RPM range
for you.


Thanks for answering Dan,

It makes more sense what you say about metal in the oil, as I was going
to post how would I know what is happening "below the top" without an
overhaul.

The engine is in a BE 23 (Beech Sundowner). I bought the plane for
$38,000 knowing a major overhaul is in my short future, but wanted to
get my learning curve behind me in this engine before overhualing it.

Right now, I get the oil changed every 30 hours, and the A&P checks for
metal every change. I plan to have the compression checked every other
oil change.

I fly it a minumum of one hour a week (even if just around the patch)
weather permitting. (I have been averaging 6 hours a week). Once I get
my instrument rating (I am starting ground school next week), I plan to
fly much more a week, as my job takes me throughout the state of MS.

Any other tips on maintaining this engine and airplane (or what to look
for) is surely appreciated. I have not seen any FAQ's on this subject,
and I am learning more from this group and hangar talk.

Allen