Priming the engine and Mag check questions

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

A Lieberman wrote in message ...
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.

Hokay. For the B-23, with Lycoming O-360-A2G, and with either
Sensenich prop number M76EMMS-0-60 or 76EM8S5-0-60, the full-throttle
static RPM should be not over 2350, not under 2250.
You'll want to make sure of the engine and prop models, to be sure
there hasn't been some STCd change in the past. The tech logs will
have this dope. The tach should be checked for accuracy, too; they're
often 100 RPM low. Most current tachs (in singles) are the magnetic
type, and the magnet weakens with time. Here in Canada we have to
check them yearly, and they can't be off by more than 4% of the
midrange cruise RPM.
Dan

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

Les Gawlik wrote:

There is a very good group on Musketeers.

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

Thanks Les for the lead on this group!

Allen

"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