Priming the engine and Mag check questions

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

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'

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

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

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

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

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

Yes, and the effect will be dramatic. The engine will shake like a
wet dog (especially a 4-banger) and the RPM drop will be both
immediate (as you noted) and very large.

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.

Maybe. It depends on which way the timing is wrong (early or late)
and how badly. Even worse, though, is what happens when the timing is
wrong because it's late. The common procedure for dealing with a
fouled plug is leaning the mixture as much as the engine will tolerate
to 'burn the plugs clean.' This actually works sometimes.

However, the nature of the ignition event is such that the flame front
propagates fastest with a mixture leaned to peak. Normally, the
engine is well rich of peak at runup power with the mixture set at
full rich.

Imagine, for a moment, what happens if the points have started to wear
on one mag and it is firing late. Unless that happens to be the only
mag with the impulse coupling, starting will not be a problem. At
runup, switching off the 'late' mag will produce a slight RPM drop -
so that part of the check is nominal. However, switching the good mag
off will cause a large RPM drop - probably more than allowable - and
some slight roughness. The pilot will then say "Aha! Plug fouling!
Let's burn those plugs clean." and proceed to lean the mixture as much
as he can. He'll run it that way for a while, then advance the
mixture only slightly (if at all) since he doesn't want to foul the
plug again. He checks the mag drops again. Now the drop will be a
little more on the good mag, and maybe a lot less on the good mag
(since it's late firing is somewhat offset by the faster combustion
event). Now the engine might just pass the mag check, and the pilot
will figure all is well - the rest will burn off in flight.

By the time this process stops working, meaning that leaning the
mixture will no longer result in a an acceptably low RPM drop, the
magneto is firing several degrees late. Not really a big deal in
cruise (especially low power cruise) but if the good mag (or even one
plug on it) decides to go during takeoff, it could really ruin your
day.

Michael

There is a very good group on Musketeers.

http://groups.yahoo.com/group/musketeermail/

The consensus is that most of the carburetted 0-360's require a lot of
prime, but like yours, they start well.


"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