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This year's annual



 
 
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  #41  
Old November 8th 06, 03:30 PM posted to rec.aviation.owning
pbc76049
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Posts: 28
Default This year's annual



Ok I am a student who is in the process go getting his A&P License and
just finished the portion dealing with what your asking..

When you run your engine at full rich you are giving the engine more
fuel than it can fully burn and use to push the cylinder down and drive
the other cylinders back up compressing the fuel air mixture. It will
continue to push but you won't get the full potential from your
compression... A way to see if your running at the correct mixture and
see if your engine is functioning to its full potentail you should
perform a MAG drop check...

To do this... after you have run your engine up and have it warm...
enrichen your mixture until it just starts to run rough then pull back
slightly... then slowly pull your throttle back to around 1700 rpm then
switch briefly while watching your tachometer to your left then back to
both and then to right and then back to both... You should see a drop
of around 50 to 75 rpm drop if your mixture is set correctly.

Daniel Brooks
A&P Pending school completion


Daniel.
You are having an apples and oranges conversation here. We are dealing
with compression checks, not reduction in BMEP due to mixture changes.
You are correct about what you are describing, but we aren't talking about
that
subject now. We ARE looking for a reason to explain WHY rich mixtures
degrade
leakdown tests. With that understood, the reason lean cut numbers are
better than
rich cut numbers is entirely due to fuel washdown. We have to remember that
we are
talking about a very small volume of air actually moving thru the oriface of
the
differential pressure gauge. Rich mixtures wash the oil off the cylinder
walls a bit more
"efficiently" than lean mixtures. The oil film between the cylinder walls
and the rings
is the sealing mechanism, NOT the rings running ON THE WALLS. If you
diminish
oil content at the sealing surface by having excess fuel there, it is fairly
obvious that
ring "blowby" will increase. A second effect, but much smaller is the
effect of excess
fuel on exhaust deposits on the exhaust valve seat. Current thinking seems
to indicate that
fuel will "wet" the deposits and cause them to stick to each other a bit
preventing
radial movement of the valve into the center of the seat. The guides also
use an
oil film to seperate the guide from the valve stem, a slight reduction in
the oil film thickness
can allow the valve to "rattle" to a position other than the center of the
guide bore. Since we
are only talking tenths here, you can start to see wht there is so much
variability in one check
to another............ ANYWAY............. These are the main reasons rich
idling will adversely effect
leakdown test results. They are proven, not conjecture. Earlier I gave
reasons from allied
fields to make the case in a more united front, but for some reason I forgot
to mention that
I'm an A&P in the game since 1979 and this particular subject hasn't changed
over the years.

Scott


  #42  
Old November 9th 06, 01:59 AM posted to rec.aviation.owning
Newps
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Posts: 1,886
Default This year's annual



B A R R Y wrote:


AFAIK, Compression tests are performed with the valves closed and the
cylinder at full compression, where a reading is taken, and possibly
watched for leakage (a diminishing reading).


There is always leakage. Unless you have a cylinder that is showing
80/80 which in my opinion is cause for alarm in itself.
  #43  
Old November 12th 06, 12:08 AM posted to rec.aviation.owning
Mike Spera
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Posts: 220
Default This year's annual



I was telling the A&P, that if it was me to pull that cylinder, I wouldn't
know what nut / bolt to crack to begin the process. He made it look so
effortless!



Don't worry. With the crap quality and 50 year old engineering common to
these airplane cylinders, you will get LOTS of opportunities to see it
done. Again and again and again...

Good Luck,
Mike
  #44  
Old November 20th 06, 03:06 PM posted to rec.aviation.owning
Greg Copeland
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Posts: 30
Default This year's annual

Wow. That's a costly ($10,000) first annual. Or maybe I'm using too
many zeros? Was any of that a surprise? Did you do a pre-buy? What
was it that cost that much? Or did you upgrade/update things while you
had it apart?

Greg

Jon Kraus wrote:
Are you ****ed that you are only getting 65 PSI compression out of a 500
SMOH hour cylinder? I think that the high copper count doesn't
necesarily mean anything drastic... Our first annual in the Mooney was
almost 10 AMU's. Our second was 5 AMU's... Following this logic maybe
this year's will be 2.5 AMU's.... Yea right!! :-)

A Lieberma wrote:
It's been a solid week, and I am still not flying in my Sundowner.....

Problems encountered.

Oil analysis came back with high count of copper
#3 cylinder low on compressions
Corrosion on a side panel of the fuselage
Small pipe (Exhaust outake?) had small crack in it
Air in the brake lines (took ten minutes to bleed)

Things to be replaced (500 hours time since major, hard to believe I have
flown that much in three years!)

Points and condensors
Mags

Things to be fixed

Windshield leakage

All has been done except for the corrosion problem. He scraped off the
paint and most of the corrosion color, but there is a pin hole size pit
(very, very tiny, but still perceptible) in the bare skin. It doesn't go
entirely through the skin, but it's there needless to say. Why in the
area is beyond comprehension since it's on a vertical surface to the
right of the door. Not exactly an area where water collects. Got a pic
if anybody's interested.

Soo, for the #3 cylinder, A&P was able to field service it and get the
compressions up to 65. Remaining three cylinders are in the 70's.

Changed the oil from 15W50 weight to 20W50 weight. Added an engine
additive too. Expensive stuff at $24 a pint!

Small pipe replaced. Brake lines bled. Windshield was sealed.

Only problem remaining to be fixed is the corrosion and repainting the
area. Hoping that what he has done will be good enough. I'd hate to see
what the cost of Beechcraft skin will do to my wallet if it can't be
fixed!

Definately won't rank in the least costly annuals for me.

Allen


 




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