Compression readings

[[email protected]]

On a Lycoming O-550, at what compression reading would you start to consider
doing a top or complete overhaul?

[Orval Fairbairn]

In article et>,
" > wrote:

> On a Lycoming O-550, at what compression reading would you start to consider
> doing a top or complete overhaul?

What is a "Lycoming "IO-550"? I know what a lycoming IO-540 is and what
a Continental IO-550 is, but -- a "Lycoming IO-550"??

[Newps]

Anybody who decides to do a complete overhaul because of low compresion
reading/s is a moron. Why is the compression low? How many hours on
the engine, etc? I bought my 182 6.5 years and 900 hours ago with 500
SMOH. My mechanic and I have since learned that the overhaul by Mid
States in Tulsa wasn't a very good one. I have had 5 of my 6 cylinders
off over the years, but just once each. It's always the valves. You
fix them and move on. Perhaps this is why Mid States is no longer in
business. No way I do a complete top much less a complete overhaul just
for bad valves. The occasional oil analysis always comes back normal.



wrote:

> On a Lycoming O-550, at what compression reading would you start to consider
> doing a top or complete overhaul?
>
>
>

[kage]

" > wrote in message
ink.net...
> On a Lycoming O-550, at what compression reading would you start to
> consider
> doing a top or complete overhaul?
>
>
>

There is no such engine.

KG

[markjen]

I agree. Compression readings are just one indicator of engine health,
along with history, oil analysis, long-term trends, etc. And some engines
are notorious for low compressions now and then - if you did a top overhaul
every time a cylinder dipped below 60, you'd never get a year without
pulling a cylinder. There is no such thing as a magic number that it a
go/no-go for doing a top.

- Mark

[Newps]

wrote:
> All these replies and not one serious answer.

They were serious, now you ask the proper question.


>
> Let me rephrase the question.
>
> On the Big Lycoming engines, at what compression reading would indicate a
> need for an investigation. In other words, what compression reading is
> considered a warning sign?

It depends. If the reading isn't in the mid 70's or above on a
particular cylinder then find out where the air is escaping and fix
accordingly. If the reading was zero you still wouldn't necessarily
overhaul the engine.

[Fly]

Dear Mr. ygaabofm
Sorry we couldn't help you. Have you tried asking NASA?


" > wrote in message
nk.net...
> All these replies and not one serious answer.
>
> Let me rephrase the question.
>
> On the Big Lycoming engines, at what compression reading would indicate a
> need for an investigation. In other words, what compression reading is
> considered a warning sign?
>
> ygaabofm
>
>
> "kage" > wrote in message
> ...
> >
> > " > wrote in message
> > ink.net...
> > > On a Lycoming O-550, at what compression reading would you start to
> > > consider
> > > doing a top or complete overhaul?
> > >
> > >
> > >
> >
> > There is no such engine.
> >
> > KG
> >
> >
>
>

[[email protected]]

First of all, thank you for answering the question.

Secondly, the first answers were not serious because it was obvious from the
answers that they did understand the question, and chose not to answer it.
There were some pretty detailed answers but none gave at what reading would
one start considering the cylinder a problem.


"Newps" > wrote in message
...
>
>
> wrote:
> > All these replies and not one serious answer.
>
> They were serious, now you ask the proper question.
>
>
> >
> > Let me rephrase the question.
> >
> > On the Big Lycoming engines, at what compression reading would indicate
a
> > need for an investigation. In other words, what compression reading is
> > considered a warning sign?
>
> It depends. If the reading isn't in the mid 70's or above on a
> particular cylinder then find out where the air is escaping and fix
> accordingly. If the reading was zero you still wouldn't necessarily
> overhaul the engine.

[[email protected]]

No. Have you tried posting something useful?


"Fly" > wrote in message
...
> Dear Mr. ygaabofm
> Sorry we couldn't help you. Have you tried asking NASA?
>
>
> " > wrote in message
> nk.net...
> > All these replies and not one serious answer.
> >
> > Let me rephrase the question.
> >
> > On the Big Lycoming engines, at what compression reading would indicate
a
> > need for an investigation. In other words, what compression reading is
> > considered a warning sign?
> >
> > ygaabofm
> >
> >
> > "kage" > wrote in message
> > ...
> > >
> > > " > wrote in message
> > > ink.net...
> > > > On a Lycoming O-550, at what compression reading would you start to
> > > > consider
> > > > doing a top or complete overhaul?
> > > >
> > > >
> > > >
> > >
> > > There is no such engine.
> > >
> > > KG
> > >
> > >
> >
> >
>
>

[Newps]

wrote:
> First of all, thank you for answering the question.
>
> Secondly, the first answers were not serious because it was obvious from the
> answers that they did understand the question, and chose not to answer it.
> There were some pretty detailed answers but none gave at what reading would
> one start considering the cylinder a problem.

You asked at what compression reading would you decide to overhaul the
engine. The answer is compression is just one factor. I had a cylinder
at one annual blow a 20/80. Doing an overhaul never entered my mind.
That cylinder turned out to be cracked. So you replace the cylinder and
move on. It's really only when your engine starts to make metal that
you contemplate overhaul. Although I had my engine make metal once,
turned out to be the shaft in my starter adapter. Replace the adapter
and the metal went away.

[[email protected]]

It just appears to me that there is a mentality that the top end or
bottom end is a single entity.
When one part needs work it's better to replace the whole part.
As far as I'm concerned, it's generally better to jusr fix the offending
problem and then continue on.
Why would anybody want to do a total OH when there is one cylinder that
needs attention, regardless of TSMOH?




Newps wrote:
>
>
> wrote:
>
>> First of all, thank you for answering the question.
>>
>> Secondly, the first answers were not serious because it was obvious
>> from the
>> answers that they did understand the question, and chose not to answer
>> it.
>> There were some pretty detailed answers but none gave at what reading
>> would
>> one start considering the cylinder a problem.
>
>
> You asked at what compression reading would you decide to overhaul the
> engine. The answer is compression is just one factor. I had a cylinder
> at one annual blow a 20/80. Doing an overhaul never entered my mind.
> That cylinder turned out to be cracked. So you replace the cylinder and
> move on. It's really only when your engine starts to make metal that
> you contemplate overhaul. Although I had my engine make metal once,
> turned out to be the shaft in my starter adapter. Replace the adapter
> and the metal went away.

[markjen]

> Secondly, the first answers were not serious because it was obvious from
> the
> answers that they did understand the question, and chose not to answer it.
> There were some pretty detailed answers but none gave at what reading
> would
> one start considering the cylinder a problem.

That's not the question you asked. You asked what compression readings
should one consider an engine overhaul. That's like asking what blood
pressure should trigger a heart transplant.

The general rule of thumb is that any cylinder below 70 should be monitored
more closely and anything below 60 should be looked at for signs of
distress. But deciding on an overhaul of this cylinder, all the cylinders,
or the entire engine would depend on wide variety of factors.

- Mark

[Orval Fairbairn]

In article <M0cvd.751595$8_6.347661@attbi_s04>,
"markjen" > wrote:

> > Secondly, the first answers were not serious because it was obvious from
> > the
> > answers that they did understand the question, and chose not to answer it.
> > There were some pretty detailed answers but none gave at what reading
> > would
> > one start considering the cylinder a problem.
>
> That's not the question you asked. You asked what compression readings
> should one consider an engine overhaul. That's like asking what blood
> pressure should trigger a heart transplant.
>
> The general rule of thumb is that any cylinder below 70 should be monitored
> more closely and anything below 60 should be looked at for signs of
> distress. But deciding on an overhaul of this cylinder, all the cylinders,
> or the entire engine would depend on wide variety of factors.
>
> - Mark

You also want to know the *quality* of the low compression reading. you
have to listen for the air leakage.

Open the oil cap and listen for air hissing into the crankcase. If so,
there is ring blowby, which may happen just because the ring ends are
lined up.

Listen to the exhaust pipe. Air escaping there indicates leaks at the
exhaust valve -- perhaps just a piece of crud temporarily under the
exhaust valve, or a burned valve or a poorly-seated valve.

Listen to the intake. Air escaping there indicates a leak at the intake
valve -- same causes as exhaust valve leaks.

Listen for air escaping around the cylinder head. Also, wet a finger and
pass it around the head and feel for any breezes. If you detect leaks
here, you have a cracked cylinder head and will have to replace it.

Places to look for cracks: around the sparkplug holes, between the
valves, around the exhaust galleys.

[nrp]

For WIW these are the compression readings from our O-320E2D Lycoming
which has 4 cyls of the same bore but less stroke as your 540. The
data is from 1977 thru 1998.

Cyl 1
70/72/67/66/71/71/70/74/72/68/72/72/72/72/68/73/73/73/74/71/66/80
(1977/....1998__)
Cyl 2
70/73/70/66/73/72/68/74/70/68/66/71/71/67/72/70/7271/71/71/80

Cyl 3
70/74/75/68/71/68/70/75/70/66/68/62/71/61/71/75/75/74/66/64/80

Cyl 4
71/70/70/66/70/69/67/70/67/68/66/72/69/71/64/70/70/73/68/70/80

As you can see sometimes some were up.... and sometimes some were down.
At 1680 hrs TTSN now, we still have never had a cyl off. Oil
consumption is still 30+ hrs/qt. When one was low or marginal, we'd
check it again in maybe 10 hrs and would usually find it up again. If
you plot it, there is a slight long term reduction in average
compression though. All readings were with the same gage (That can be
a big variable too).

Compression data since then isn't on this computer, but it hasn't
really changed its characteristics. I have the data elsewhere.

John Thorpe also once said that taking the upper spark plug out before
doing a compression test will cause debris to fall on any open valve,
giving a false low reading.

[Jay Honeck]

> Cyl 1
> 70/72/67/66/71/71/70/74/72/68/72/72/72/72/68/73/73/73/74/71/66/80
> (1977/....1998__)
> Cyl 2
> 70/73/70/66/73/72/68/74/70/68/66/71/71/67/72/70/7271/71/71/80
>
> Cyl 3
> 70/74/75/68/71/68/70/75/70/66/68/62/71/61/71/75/75/74/66/64/80
>
> Cyl 4
> 71/70/70/66/70/69/67/70/67/68/66/72/69/71/64/70/70/73/68/70/80

You didn't find it all suspicious that the last (1998) readings were all
*perfect*?

Personally, I'd be checking my procedures or my gauge. Ain't no way those
cylinders all jumped from merely okay to all "80"s -- especially since they
were NEVER "80"s, even in back in '77.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Darrel Toepfer]

Jay Honeck wrote:
>>Cyl 1
>>70/72/67/66/71/71/70/74/72/68/72/72/72/72/68/73/73/73/74/71/66/80
>>(1977/....1998__)
>>Cyl 2
>>70/73/70/66/73/72/68/74/70/68/66/71/71/67/72/70/7271/71/71/80
>>
>>Cyl 3
>>70/74/75/68/71/68/70/75/70/66/68/62/71/61/71/75/75/74/66/64/80
>>
>>Cyl 4
>>71/70/70/66/70/69/67/70/67/68/66/72/69/71/64/70/70/73/68/70/80
>
>
> You didn't find it all suspicious that the last (1998) readings were all
> *perfect*?
>
> Personally, I'd be checking my procedures or my gauge. Ain't no way those
> cylinders all jumped from merely okay to all "80"s -- especially since they
> were NEVER "80"s, even in back in '77.

Geez Jay, thats the reference pressure...

[G.R. Patterson III]

Darrel Toepfer wrote:
>
> Jay Honeck wrote:
> >>Cyl 1
> >>70/72/67/66/71/71/70/74/72/68/72/72/72/72/68/73/73/73/74/71/66/80
> >>(1977/....1998__)
> >>Cyl 2
> >>70/73/70/66/73/72/68/74/70/68/66/71/71/67/72/70/7271/71/71/80
> >>
> >>Cyl 3
> >>70/74/75/68/71/68/70/75/70/66/68/62/71/61/71/75/75/74/66/64/80
> >>
> >>Cyl 4
> >>71/70/70/66/70/69/67/70/67/68/66/72/69/71/64/70/70/73/68/70/80
> >
> >
> > You didn't find it all suspicious that the last (1998) readings were all
> > *perfect*?
> >
> > Personally, I'd be checking my procedures or my gauge. Ain't no way those
> > cylinders all jumped from merely okay to all "80"s -- especially since they
> > were NEVER "80"s, even in back in '77.
>
> Geez Jay, thats the reference pressure...

If it is, then there aren't enough readings for the years 1977 to 1998.

George Patterson
The desire for safety stands against every great and noble enterprise.

[nrp]

> If it is, then there aren't enough readings for the years 1977 to
1998.

The annuals sometimes took advantage of the calendar year effect, so
they tended to be slightly more than a year apart. Hence there ended
up being an apparent year missed.
The last listing was the common reference pressure.

[Jay Honeck]

> The annuals sometimes took advantage of the calendar year effect, so
> they tended to be slightly more than a year apart. Hence there ended
> up being an apparent year missed.
> The last listing was the common reference pressure.

Ah -- that's what threw me.

Thanks for the clarification...
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"